Ultrasonography Imaging Versus Waveform Capnography in Detecting Endotracheal Tube Placement During Intubation in a Tertiary Hospital.
Conditions: Intubation, Ultrasound Imaging, Capnography
Sponsor: Tribhuvan University, Nepal

1 
 
ABSTRACT 
Background: 
After endotracheal intubation verifying the location of endotracheal tube is of utmost 
importance. Many methods have been applied but none is perfect. The standard 
practice is to use auscultation of chest with capnography. Ultrasound machines are 
now gaining popularity and their access extends from operation theatres, emergency 
rooms and even many primary health centres. Both capnography and ultrasonography 
are proven to be safe. This study aims to see if ultrasonography can also be made a 
routine method of endotracheal tube position confirmation inside operating theatres 
along with capnography. 
Methods: 
This was a prospective, observational study conducted at the Tribhuvan University 
Teaching Hospital (TUTH) and Manmohan Cardiothoracic Vascular and Transplant 
Center (MCVTC) operating rooms from January 2017 to July 2017. Ethical approval 
from the Institutional Review Board (IRB) of Institute of Medicine (IOM) and the 
Department of Anaesthesiology, Maharajgunj Medical College (MMC) was taken. 
Written informed consent was taken. 
ASA I and II patients over 16 years of age were included in this study. Patients with 
difficult airway and anticipated difficult intubation, respiratory diseases, poor 
functional status, emergency case, and patients at risk of aspiration were excluded.  
The diagnostic characteristics of real-time, suprasternal, transtracheal ultrasonography 
and capnography were tested by calculating their respective sensitivities, specificities, 
positive predictive values (PPV), negative predictive values (NPV), accuracies and 
likelihood ratios. Comparison of time taken for confirmation of endotracheal tube 

2 
 
position from the beginning of laryngoscopy, by ultrasonography versus capnography 
was done using t-statistics.  
The degree of agreement of result between ultrasonography and capnography was 
tested with kappa statistics. 
Results: 
Out of the 95 patients studied, 11 had oesophageal intubation (Incidence of 11.57%). 
The overall accuracy of both ultrasonography and capnography was 96.84%. The 
sensitivity, specificity, PPV, NPV with their corresponding 95% confidence intervals 
(CI) for ultrasonography were 97.62% (91.66% - 99.71%), 90.91% (58.72% - 
99.77%), 98.80% (92.67% - 99.81%), 83.33% (55.66% - 95.22%) respectively; and 
that for capnography were 96.43% (89.92% - 99.26%), 100% (71.51% - 100%), 100% 
(100% - 100%) and 78.57% (54.69% - 91.76%) respectively.  
The likelihood ratio of a positive and a negative result for ultrasonography were 10.74 
and 0.03 respectively, and that for capnography were infinity and 0.04 respectively.  
The kappa value was 0.749 (95% CI: 0.567 – 0.931) which meant a good degree of 
agreement of result between these two methods. 
The average time taken for confirmation of endotracheal tube by ultrasonography and 
capnography were 26.79 ± 7.64 seconds and 43.03 ± 8.71 seconds (mean ± standard 
deviation) respectively. The median time for confirmation was 26 seconds with 
interquartile range [15 - 37] seconds for ultrasonography and 42 seconds with 
interquartile range [29 - 55] seconds for capnography. Ultrasonography was found to 
be faster than capnography by 16.36 ± 3.23 seconds (mean ± standard deviation) and 
the difference in time was significant (p = 0.011). 

3 
 
Conclusion: 
Ultrasonography and waveform capnography are both reliable and accurate methods 
of confirming endotracheal tube position. The use of ultrasound with capnography 
will help reduce time and increase precision of confirming endotracheal tube position. 
Ultrasound can confirm endotracheal tube position before manual bag ventilations, 
and thus may prevent aspiration of gastric contents into patient’s lungs. 
 
Keywords: Endotracheal intubation; ultrasonography; capnography. 
 
 
 
 
 
 
 
 
 
 
 
 
 

4 
 
TABLE OF CONTENTS 
 
Serial No. 
 
Contents 
 
 
 
 
 
Page No. 
1 
Introduction  
 
 
 
 
 
 
7 
2 
Literature Review 
 
 
 
 
 
19 
3 
Objectives 
 
 
 
 
 
 
30 
4 
Hypothesis 
 
 
 
 
 
 
31 
5 
Methodology 
 
 
 
 
 
 
32 
6 
Results  
 
 
 
 
 
 
45 
7 
Discussion 
 
 
 
 
 
 
55 
8 
Limitations  
 
 
 
 
 
 
68 
9 
Conclusion 
 
 
 
 
 
 
69 
10 
Recommendations 
 
 
 
 
 
70 
11 
References 
 
 
 
 
 
 
71 
12 
Appendices 
Appendix A - PAC Form 
 
 
 
 
77 
Appendix B - Consent  
 
 
 
 
79 
Appendix B – Proforma 
 
 
 
 
80 
Appendix D – Thesis approval letter from IRB 
 
82 
 
 
 
 
 
 

5 
 
 
LIST OF ABBREVIATIONS 
% 
 
 
Percentage 
>  
 
 
Greater than 
<  
 
 
Lesser than 
± 
 
 
Plus– Minus 
α 
 
 
Alpha 
ACLS                         Advanced Cardiac Life Support 
AHA  
 
American Heart Association 
ASA  
 
American Society of Anesthesiologists 
β 
 
 
Beta 
BMI 
 
 
Body Mass Index 
BPM  
 
Beats Per Minute 
CI 
 
 
Confidence Interval 
CL 
 
 
Cormack Lange 
CO2 
 
 
Carbon Dioxide 
COPD                         Chronic Obstructive Pulmonary Disease 
CPR 
 
 
Cardiopulmonary Resuscitation  
DLT 
 
 
Double-Lumen Tube 
ECG  
 
Electrocardiogram 
Eg  
 
 
Example 
ET 
 
 
Endotracheal 
ETCO2  
 
End Tidal CO2 
NIBP  
 
Non-Invasive Blood Pressure 
IRB 
 
 
Institutional Review Board 

6 
 
IOM 
 
 
Institute of Medicine 
IQR 
 
 
Interquartile Range 
κ 
 
 
Kappa value 
Kg 
 
 
kilogram 
LMA  
 
Laryngeal Mask Airway 
LR+ 
 
 
Likelihood ratio of a positive test 
LR- 
 
 
Likelihood ratio of a negative test 
MCVTC 
 
Manmohan Cardiothoracic Vascular and Transplant Center 
MMC  
 
Maharajgunj Medical Campus 
mg 
 
 
milligram 
mm 
 
 
millimeter 
NPV  
 
Negative Predictive Value 
OT 
 
 
Operation Theater 
PAC 
 
 
Preanaesthetic Checkup 
PEEP  
 
Positive End Expiratory Pressure 
PPV 
 
 
Positive Predictive Value 
PVC 
 
 
Polyvinyl Chloride 
Sec 
 
 
Seconds 
SEM  
 
Standard Error of Mean 
SpO2  
 
Oxygen saturation of Hemoglobin 
TRUE  
 
Tracheal Rapid Ultrasound Examination 
TU 
 
 
Tribhuvan University 
TUTH  
 
Tribhuvan University Teaching Hospital 
USA                            United States of America 
USG  
 
Ultrasonography 

7 
 
INTRODUCTION 
 
Endotracheal intubation is regarded as the gold standard for airway management in 
anaesthesia practice.1 It establishes a definitive airway, provides maximal protection 
against aspiration of gastric contents, and allows for positive pressure ventilation.  
The modern, standard endotracheal tube is disposable, made for single-use; and is a 
cuffed, polyvinyl chloride tube designed to be inserted through the nasal or oral 
orifice. The tip of the tube sits distally at the midtrachea. Oesophageal and 
endobronchial intubation lead to significant anaesthesia related morbidity and 
mortality, which in most circumstances are avoidable.1 
Endotracheal tube placement can be determined in the operating room by various 
methods1-3: 
• Direct visualization of passage of endotracheal tube between vocal cords 
• Bilateral chest rise during ventilation 
• Visible condensation in the endotracheal tube 
• Auscultation: equal breath sounds heard bilaterally over the chest wall and 
lack of breath sounds over the epigastrium  
• Large exhaled tidal volumes 
• Appropriate compliance of the reservoir bag  during manual ventilation  
• Capnography 
• Fiberoptic bronchoscopy 
• Ultrasonography 
• Oesophageal detection devices, chest radiography which are less feasible 

8 
 
The ideal method for confirmation of endotracheal tube placement should be fast, 
simple, reliable and safe.3 Visualization of passage of endotracheal tube through the 
vocal cords and waveform capnography showing sustained detection of exhaled 
carbon dioxide are the gold standard methods to confirm endotracheal tube  
placement.4 Capnography is the most important objective method to confirm 
endotracheal tube placement1; and has been included into the ASA standards of 
monitoring.5 None of these methods including capnography fulfill all the credentials 
of an ideal method.3 No single method can be completely relied upon especially 
during emergency intubations.6 Most of these methods require bag ventilations which 
may lead to aspiration of gastric contents in the advent of oesophageal intubation. 
Objective monitors and techniques may not be widely accessible or may be difficult 
to learn and operate. Therefore adjunctive methods have to be added to the current 
standard practice to increase precision, reduce time and prevent hazards of 
oesophageal intubation.6 
Exhaled CO2 measurement 
Capnometry is the measurement and numeric representation of the carbon dioxide 
(CO2) concentration during inspiration and expiration.7 A capnograph, however, is a 
device that records and displays CO2 concentrations as a function of time or volumes.8 
A time capnogram is a continuous concentration–time display graphically of the CO2 
concentration sampled from a mixture of gases at a patient’s airway during 
ventilation. The time capnogram is divided into four distinct phases7: 
 

9 
 
 
Fig.1. Normal capnogram showing a regular CO2 waveform.7(p705) 
 
The first phase [A–B], also known as phase I, represents the initial stage of expiration. 
Gas sampled during this phase occupies the anatomic dead space and is normally 
devoid of CO2. At point B, CO2 containing gas between the airways and alveoli 
presents itself at the sampling site and a sharp upstroke of the second phase [B–C] or 
phase II is seen in the capnogram. Phase III [C–D], represents expiratory plateau from 
the alveolar gas which is now sampled. There is slight up sloping of CO2 
concentration versus time during phase III due to heterogeneous distribution of 
ventilation-perfusion or alveolar CO2 partial pressure throughout the lungs. The term 
“end-tidal” CO2 (ETCO2) generally refers to the final value of the exhaled CO2 curve, 
at the very end of the expiratory phase. As the patient begins to inspire, fresh gas is 
entrained and there is a steep down stroke [D–E] of the phase IV, back to baseline. 
Unless rebreathing of CO2 occurs, the baseline approaches zero.7,8 
The angle between Phases II and III is called the α angle, or the takeoff or elevation 
angle. Normally, it is between 100 and 110 degrees. Airway obstruction, eg. during 
bronchospasm, and PEEP cause a larger α angle and hence an increased slope in the 
waveform at C-D. The angle between the end of Phase III and the descending limb of 
β 
I
α 
IV 
III 
II 

10 
 
the capnogram in phase IV is called the β angle. Normally, it is approximately 90 
degrees. The angle is increased with rebreathing.2 
ETCO2 is the best reflection of the alveolar CO2 (PACO2). The ETCO2–PACO2 
gradient typically is around 5 mm Hg during routine general anaesthesia in otherwise 
healthy, supine patients. ETCO2 value usually ranges between 35-45 mm of Hg.7 The 
presence of CO2 in exhaled breath assures the anaesthesiologist of correct placement 
of an endotracheal tube or laryngeal mask airway (LMA), as well as the integrity of 
the breathing circuit.8 
ETCO2 monitoring devices fall into 3 categories: colorimetric (changes color), 
capnometric (numeric; quantitative display), or capnographic (numeric display with 
waveform; qualitative display). Colorimetric devices require sufficient exhalation 
time up to 6 successive ventilations for change of color to occur. A perfusing cardiac 
rhythm and uncontaminated device are the prerequisites of these devices. Airway 
secretion affect the reliability of the colorimetry.9 They are now rarely available 
commercially. 
The most commonly used method of detecting CO2 in respiratory gases is non-
dispersive infrared absorptiometry. Absorption of infrared light by CO2 is governed 
by the Beer–Lambert law.8 There are two general categories of capnographs: 
sidestream (diverting) and mainstream (nondiverting). Sidestream analyzers have CO2 
sensors physically located away from the endotracheal tube and ventilator circuit to 
measure airway gases. Sidestream analyzers have a transport delay time 
corresponding to the rate at which gas is sampled from the anaesthesia ventilator 
circuit. The time delay is also affected by the rate of washout of previously sampled 
gas from the analyzing chamber. In mainstream analyzers, the sample sensor cell is 

11 
 
placed directly into the patient’s breathing circuit. The inspiratory or expiratory gases 
pass directly through the infrared light path and thus they have no delay time.8 
The presence of exhaled CO2 for six successive breaths indicates that the endotracheal 
tube is not in the oesophagus. Most capnographs provide a quantitative ETCO2 value 
(capnometry) as well. However it is the capnography reading of regular waves and not 
sole quantitative ETCO2 value that is the gold standard for endotracheal tube 
confirmation.10 CO2 may be falsely read by capnometers initially because of presence 
of CO2 due to gastric insufflation during bag and mask ventilation, or due to ingestion 
of carbonated drinks by the subject. The ETCO2 value slowly decreases to 
undetectable during oesophageal intubation in such cases.3,9,10 In the event of 
oesophageal intubation, the six breaths allow the CO2 in the stomach to disperse.11 
The capnogram will have an abnormal configuration and be irregular in such cases.2 
An ETCO2 value greater than or equal to 5 mm of Hg after six ventilations also 
suggests that the endotracheal tube is not in the oesophagus.12 
In a study comparing auscultation, capnometry and capnography for endotracheal 
tube confirmation, Grmec12 found that auscultation is unreliable compared to 
capnometry and capnography. While the sensitivity and specificity of capnography 
were both 100% in 345 emergency intubations including both cardiac arrest and non-
arrest patients, the sensitivity and specificity of capnometry were 88% and 100% 
respectively. In their study, there were 28 false negatives in capnometry which were 
all cardiac arrest cases. Similar results showing better reliability of capnography over 
capnometry was found by Ornato et al13, Macleod et al14, and Bozeman et al15. 
 

12 
 
A continuous, stable CO2 waveform ensures the presence of alveolar ventilation but 
does not necessarily indicate that the endotracheal tube is properly positioned in the 
trachea. Endotracheal tube placed proximally to the vocal cords may still produce an 
otherwise satisfactory tracing until it becomes dislodged. An endobronchial intubation 
cannot be ruled out until breath sounds are auscultated bilaterally. Capnography is 
also unreliable for endotracheal tube confirmation during low pulmonary flow states, 
and also during bronchospasm or a kinked endotracheal tube.4 Though the American 
Heart Association (AHA) has incorporated presence of capnograph waveforms and 
ETCO2 value greater than 10 mm of Hg as sign of effective chest compressions in the 
Advanced Cardiac Life Support (ACLS) algorithm16; capnography is regarded to be 
unreliable during cardiopulmonary resuscitation1,2,7 and also with adrenaline use.6 
 
 
 
 
Fig. 2. Normal waveform capnogram during tracheal intubation.8(p1554) 
 
Fig. 3. Irregular waveform capnogram during oesophageal intubation.8(p1554) 
 

13 
 
Ultrasonography 
Ultrasonography is now being increasingly used in medical practice as a bedside point 
of care utility. It is safe, quick in learned hands, portable and widely available in 
different departments of a hospital or other health facilities.17 Applications of 
ultrasound imaging in airway management can be as follows17,18: 
• Identification of position of endotracheal tube during intubation 
• Assessment of the diameter of the subglottic upper airway and prediction of 
endotracheal tube size, including pediatric endotracheal tube size and double-
lumen tube size 
• Detection of subglottic stenosis, prediction of post-extubation stridor 
• Guidance of percutaneous dilatational tracheostomy and cricothyroidotomy 
• Prediction of difficult intubation through measurements of various airway 
parameters 
• Ultrasound-guided upper airway anaesthesia to facilitate awake intubation 
• Detection of laryngeal mask airway position 
• Diagnosis of upper airway pathologies, e.g. soft tissue masses 
For the purpose of endotracheal tube confirmation, a high frequency linear ultrasound 
probe (9 – 13 Megahertz) is used. The probe is placed in transverse orientation just 
0.5 to 1 cm above the suprasternal notch (Fig. 4).19 
Normally trachea appears as a hyperechoic curvilinear structure with comet-tail 
artifact and shadowing (reverberations from the air-mucosa interfaces). The 
oesophagus is usually seen more distally, posterolateral and to the left of trachea, as 
an oval structure with concentric layers comprising of hyperechoic wall layers and 
hypoechoic center (Fig. 5).19,20 

14 
 
 
 
Fig. 4. Position of linear ultrasound probe just above the suprasternal notch.  
 
 
(A)                                                        (B) 
 
Fig. 5. (A) Normal suprasternal airway anatomy in ultrasound.20                        
(B) Ultrasound image focused to show trachea and oesophagus. Comet tail artifact 
inside the curvilinear acoustic shadow of the trachea is seen.19                         
(t=trachea, e=oesophagus, ca=common carotid artery) 
 

15 
 
The operator should slide and maintain the transducer probe slightly to the patient’s 
left and optimize the image depth to ensure that the posterior position of oesophagus 
is well visualized.20 
Successful endotracheal intubation will demonstrate an increase in artifact and 
shadowing in the region of the trachea only. Performing a slight shaking of the ET 
tube will only show movement and fluttering inside of the trachea. If color Doppler is 
used during the movement of the tube, a color ray will be seen inside the tracheal 
acoustic shadow (Fig. 6).19 
 
Fig. 6. Presence of endotracheal tube in trachea in Color Doppler.19 
In oesophageal intubation, real-time ultrasound will reveal an adjacent hyperechoic 
curvilinear structure with shadowing being manipulated through the oesophageal 
lumen, and comet-tail artifact posterolateral to the trachea, (double tract sign).19 
Absence of these signs indirectly confirms tracheal placement of the tube. (Fig. 7) 
If the oesophagus is located directly posterior to the trachea, an oesophageal 
intubation may be missed as this second hyperechoic structure will be obscured by the 
shadowing from the trachea.19 To minimize this, as mentioned earlier, the probe has to 

16 
 
be adjusted slightly to the left side of neck for proper visualization of the oesophagus 
including its posterior wall, prior to passing of the endotracheal tube.20 Limitations of 
ultrasound also include wave scattering and acoustic artifacts generated in air-mucosa 
interfaces. Similarly presence of anatomical abnormalities in anterior neck and trauma 
or infection at the anterior neck, hamper the use of ultrasound at the suprasternal 
site.18 
 
Fig. 7. Endotracheal tube in the oesophagus in ultrasound image. Presence of 
color Doppler ray outside of the trachea along with double tract sign.19 
 
Another method described is to place the probe in transverse orientation at the level of 
vocal cords and see for fluttering at vocal cords or vocalis ligament in ultrasound as 
the endotracheal tube passes through. Tracheal ultrasound can also be done at the 
cricothyroid membrane level to see the placement of endotracheal tube.18 Additional 
sonographic way to identify endotracheal tube placement confirmation includes 
visualizing bilateral lung sliding while bagging the paralyzed patient.17 

17 
 
As opposed to capnography and auscultation, ultrasonography enables clinicians to 
identify oesophageal intubation prior to delivering ventilatory breaths through the 
endotracheal tube, potentially decreasing the risk of gastric insufflation and 
subsequent aspiration. 
Tracheal ultrasonography is not affected by low pulmonary flow or bronchospasm 
unlike in capnography.1,17,20 
The current practice in anaesthesia is to use the combination of auscultation and 
capnography waveform observation for endotracheal tube confirmation in most 
centres including in IOM (Institute of Medicine), at TUTH (Tribhuvan University 
Teaching Hospital) and MCVTC (ManMohan Cardiothoracic Vascular and 
Transplant Center). But the capnography infrared sensor monitors are not widely 
available in Nepal. Also the matter of endotracheal tube confirmation is sensitive, it 
has to be done quickly prior to decreasing oxygen levels in the patient and aspiration 
of stomach contents into lungs has to be prevented. The practice of using capnography 
and auscultation requires repeated manual ventilations for endotracheal tube 
confirmation, and thus frequently falls short in this matter when compared to 
ultrasonography.3,6,21 
Rationale 
Both capnography and ultrasound are safe and have been shown to be reliable 
methods of endotracheal tube confirmation in previous studies which will be detailed 
further in literature review section. Physicians with basic knowledge about these 
methods can use them in operating rooms and also in emergency rooms and wards. 
Ultrasound machines are now gaining popularity and their access extends from 
operation theatres, emergency rooms and even many primary health centres in Nepal.  

18 
 
Conducting this study will help us to see if ultrasound when used along with 
capnography can reduce time taken and increase precision for endotracheal tube 
confirmation inside operating theatres; and further advocate use of ultrasound imaging 
prior to manual ventilation for endotracheal tube confirmation in full stomach or 
patients at risk of aspiration. 
 
 

19 
 
LITERATURE REVIEW 
 
 
A review article published in Journal of Intensive Care Medicine, October 2009 by 
Rudraju and Eisen3 discussed the effectiveness and pitfalls of the conventional and 
unconventional methods of endotracheal tube confirmation. None of the methods they 
reviewed had 100% sensitivity and 100% specificity. The best sensitivity and 
specificity in their opinion would be possessed by fiberoptic bronchoscopic 
visualization of the carina, trachea and bronchi. But this would be impractical because 
of availability constraint and inexperience of the operator. Secretions, blood or gastric 
contents would hamper fiberoptic visualization as well. The visualization of passing 
of endotracheal tube into the vocal cords was also stated to be unreliable. They have 
cited anatomical irregularities like large tongue, prominent teeth, short neck and blood 
and secretions as causing difficulty in visualization of vocal cords frequently.22 They 
have concluded that waveform capnography would be the best practical and reliable 
method through numerous citations.12,22-24 Similar conclusion was also reached by 
DeBoer et al9 in their review article. In conditions where capnography could be 
unreliable as in cardiac arrest and bronchospasm, they have suggested few 
alternatives. Oesophageal suction detection devices could be useful as these do not 
require presence of pulmonary blood or airflow, but they have cited these devices to 
have low sensitivity of 80% and good specificity of 97%.25 They have suggested 
ultrasonography to be good alternative method but they argued that more studies were 
required to establish ultrasound use during intubation.3  
 
 

20 
 
In a study done by Knapp et al26 in 1999, they evaluated four different methods of 
endotracheal tube position confirmation: auscultation, capnography, oesophageal 
detection device which operated using suction, and transillumination method with a 
lighted stylet wand. They enrolled 38 participants. The subjects were first tracheally 
intubated and connected to a ventilator. Then a second endotracheal tube was passed 
into the oesophagus by laryngoscopy. Two blinded examiners, one an experienced (4 
years worked in critical care) and another inexperienced (medical student) were then 
asked to identify the position of one of the tubes each in a subject, using one of the 
four methods. The method to be used to verify tube position, and the particular tube to 
be identified in a subject by an examiner, were randomized using allocation numbers. 
At the end of 152 examinations, both examiners correctly identified the tube position 
using capnography in all cases. Using auscultation, experienced examiner was correct 
in all cases, but the inexperienced examiner was correct in 68% cases only. Using the 
oesophageal detection device, there were two wrong results by experienced examiner 
and one wrong result by the inexperienced examiner. Using the transillumination 
method, the experienced examiner was wrong in 16% cases and the inexperienced 
examiner was wrong in 13% cases.  Thus, capnography was found to be the most 
reliable method of endotracheal tube confirmation followed by oesophageal detection 
device. Capnography was statistically superior to auscultation and transillumination. 
Oesophageal detection device did not show statistical superiority to auscultation and 
transillumination however. They also concluded that auscultation is largely dependent 
on the experience of the operator.26 
 
 

21 
 
Grmec12 also found similar results as that of Knapp et al26 when comparing 
auscultation, capnometry and capnography for endotracheal tube confirmation. He 
tested 345 emergency intubations in a prehospital unit at Maribor, Slovenia from 
February 1998 to February 2001. 246 were cardiac arrest patients and 79 were non-
cardiac arrest patients. In non-arrest patients, capnometry had both sensitivity and 
specificity of 100%; capnography also had both sensitivity and specificity 100% but 
auscultation had sensitivity of 94% and specificity of 83% in confirming endotracheal 
tube placement. Capnometry was highly specific (100%) but not sensitive (88%) for 
correct endotracheal intubation in patients with cardiopulmonary arrest while 
capnography again had both sensitivity and specificity of 100%. They concluded that 
capnography was the most reliable method to confirm endotracheal tube placement in 
emergency conditions in the prehospital setting.12 
 
A meta-analysis was done by Li24 on the use of end tidal CO2 detection methods for 
endotracheal tube confirmation. 512 trials were processed from the National Institute 
of Health (USA) database from 1996 to 1999. Trials that included human subjects in 
whom emergency endotracheal intubation had been done, where the tube position was 
checked by a device measuring end tidal CO2 and the result compared with another 
method of verification of tube position as standard, were chosen. He also excluded 
trials where number of tracheal and oesophageal intubations were not shown as part 
of the secondary objective. 10 trials were finalized and 2192 intubation were included. 
Tube placement for 444 out of 2192 intubations (20%) had been tested with infrared 
devices, and placement for 1748 out of 2192 intubations (80%) had been tested with 
colorimetric devices. The results showed an aggregate sensitivity of 93% (95% 
confidence interval (CI): 92 – 94%) and an aggregate specificity of 97% (95% 

22 
 
confidence interval (CI): 93 - 99%) of capnography devices for emergency 
endotracheal tube placement confirmation. The false-negative failure rate (tube in 
trachea but capnography reported oesophagus) was 7% and the false-positive rate 
(tube in oesophagus but capnography reported trachea) was 3%. This was translated 
to potential harm for one patient in every 10 emergency intubations verified with 
exhaled CO2 device alone. Two trials among the ten included, reporting on 721 
intubations (33% of the total), had demonstrated no difference in accuracy between 
the colorimetric or infrared devices end-tidal capnography for tube placement 
confirmation during emergency airway management. Secondary objectives were to 
see the rate of unanticipated oesophageal placement during emergency intubation and 
quantification of the portion of intubations performed in patients with cardiac arrest. 
The data was taken from the National Emergency Airway Registry. Of 4602 
consecutive intubations, 4% of emergency intubation attempts had resulted in 
accidental oesophageal intubation, and 10% had occurred in non-traumatic cardiac 
arrest patients. He concluded that misidentification of oesophageal endotracheal tube 
placement in the emergency setting may occur with capnography. His 
recommendation was to use multiple methods of tube placement confirmation method 
because no single method has perfect accuracy.24 
 
Chou et al6 did a systematic review and meta-analysis to check the evidence of 
diagnostic value of ultrasonography for the assessment of endotracheal tube 
placement in adult patients. Any method of ultrasonography to confirm endotracheal 
tube placement was selected. Exclusion criteria included case reports, comments, 
reviews, guidelines and animal studies. 1334 studies were processed, 75 of these were 
selected. A total of 12 eligible studies were taken for final analysis which had 1656 

23 
 
intubation attempts. Tracheal ultrasonography was used in ten studies and lung 
ultrasonography was used in four studies, two studies used both tracheal and lung 
ultrasonography to confirm endotracheal tube placement. Seven studies used 
capnography or ETCO2 detectors as criterion standard of tracheal intubation whereas 
the remaining studies used direct laryngoscopy, chest auscultation, or chest 
radiography. For detection of oesophageal intubation, the pooled sensitivity of 
ultrasonography was 0.93 (95% CI: 0.86–0.96) and the specificity was 0.97 (95% CI: 
0.95–0.98). The positive and negative likelihood ratios were 26.98 (95% CI: 19.32–
37.66) and 0.08 (95% CI: 0.04–0.15) respectively. A hierarchical summary receiver 
operating characteristic curve that plots sensitivity versus specificity was constructed 
and the area under the curve was calculated to be 0.97 (0.95–0.98). In tracheal 
ultrasonography, attending physicians demonstrated superior sensitivity (0.98, 95% 
CI: 0.96–0.99) when compared to resident physicians (0.92, 95% CI: 0.78–0.96). 
Tracheal ultrasonography performed in the emergency had a lower sensitivity (0.88, 
95% CI: 0.76–0.94) in comparison to other settings. Tracheal ultrasonography 
performed in real-time was associated with superior sensitivity (0.94, 95% CI: 0.86–
0.98) than that performed post-intubation in static manner (0.91, 95% CI: 0.70–0.98). 
They concluded that ultrasonography had high diagnostic value for identifying 
oesophageal intubation. They recommended ultrasonography be used as a valuable 
adjunct in endotracheal intubation confirmation, especially in situations where 
capnography may be unreliable.6 
 
A systematic review and meta-analysis was also done by Das et al21 in 2015 to 
evaluate the diagnostic accuracy of transtracheal ultrasound in detecting endotracheal 
intubation. Eleven studies and 969 intubations were included in the final analysis. 

24 
 
Eight studies and 713 intubations had been performed in emergency situations and the 
others were carried out in elective situations. Transtracheal ultrasonography’s pooled 
sensitivity and specificity with 95% confidence interval (CI) were 0.98 (95% CI: 0.97 
- 0.99) and 0.98 (95% CI: 0.95 - 0.99) respectively. In emergency scenarios, 
transtracheal ultrasonography showed an aggregate sensitivity and specificity of 0.98 
(95% CI: 0.97 - 0.99) and 0.94 (95% CI: 0.86 - 0.98) respectively. Transtracheal 
ultrasound was concluded to be a useful tool to confirm endotracheal intubation. They 
recommended that transtracheal ultrasonography could be used as a preliminary test 
for endotracheal intubation before final confirmation by capnography.21 
 
Karacabey et al27 did a study to evaluate accuracy and speed of ultrasonography  for 
confirming endotracheal tube placement by tracheal ultrasound and lung sliding. They 
also observed the degree of agreement of ultrasonography when used for endotracheal 
tube confirmation along with capnography as the standard method. The study was a 
prospective, single-centre, observational study conducted in the emergency 
department of a tertiary care hospital. Patients who had emergency intubation because 
of respiratory failure, cardiac arrest or severe trauma were included. A total of 115 
patients were included in the study. Among 115 patients, 30 were cardiac arrest 
patients. The overall accuracy of the ultrasonography in their study was 97.18% (95% 
CI: 90.19% – 99.66%), and the value of kappa was 0.869 (95% CI: 0.77 – 0.96) 
indicating a high degree of agreement between ultrasonography and capnography. 
Ultrasonography took significantly less time than capnography, mean of 5.8 seconds 
versus 11.7 seconds respectively.27 
 
 

25 
 
Chou et al28 in 2010 had compared real-time suprasternal transtracheal ultrasound to 
waveform capnography as the standard for endotracheal tube confirmation. The 
position of trachea was identified by a hyperechoic air–mucosa interface with 
posterior reverberation artifact (comet-tail artifact). The endotracheal tube position 
was defined as endotracheal if single air-mucosa interface with comet-tail artifact was 
observed. A total of 112 emergency intubations were included in the analysis, and 17 
(15.2%) had oesophageal intubations. The overall accuracy of the ultrasound was 
98.2% (95% CI: 93.7–99.5%). The kappa value was 0.93 (95% CI: 0.84–1.00), 
indicating a high degree of agreement. The sensitivity, specificity, positive predictive 
value, and negative predictive value of the ultrasound were 98.9% (95% CI: 94.3–
99.8%), 94.1% (95% CI: 73.0–99.0%), 98.9% (95% CI: 94.3–99.8%) and 94.1% 
(95% CI: 73.0–99.0%) respectively. The median operating time of the ultrasound was 
9.0 sec [Interquartile Range (IQR): 6.0 - 14.0 sec].28 
Chou and his colleagues did another study29 from 2010-2012, using the same method 
of real-time suprasternal  tracheal ultrasonography for assessing endotracheal tube 
position during cardiopulmonary resuscitation, but this time they had limited their 
ultrasound use time to not more than 10 seconds. They tested the diagnostic accuracy 
of ultrasonography in a limited time frame of 10 seconds. Among the 89 patients 
enrolled, 7 (7.8%) had oesophageal intubations. The sensitivity, specificity, positive 
predictive value, and negative predictive value of tracheal ultrasonography in this 
study were 100% (95% CI: 94.4–100%), 85.7% (95% CI: 42.0–99.2%), 98.8% (95% 
CI: 92.5–99.0%) and 100% (95% CI: 54.7–100%) respectively. Positive and negative 
likelihood ratios were 7.0 and 0.01 respectively. Thus they concluded that ultrasound 
had a good diagnostic ability to detect endotracheal intubation, and the confirmation 
could well be performed under 10 seconds. They had used capnography as the 

26 
 
standard method of endotracheal tube confirmation after the results of ultrasound 
were obtained, and they had not seen the time taken for confirmation by 
capnography.28,29 
 
Adi, Chaun and Rishya30 published a study in Critical Care Ultrasound Journal in 
2013. They compared bedside upper airway ultrasonography to waveform 
capnography for verification of endotracheal tube location after intubation. It was a 
prospective, observational study conducted at a single centre in Taiwan. The study 
included patients who were intubated in the emergency department from 28 March 
2012 to 17 August 2012. They scanned the anterior area of neck of patients first in 
horizontal view to see two parallel hyperechoic lines in trachea for tracheal intubation 
or absence of this with dilatation of oesophagus in oesophageal intubation. Then they 
reconfirmed with ultrasound in the vertical view to see for presence or absence of two 
hyperechoic lines. A sample of 107 patients was finalized based on the desired 
precision of 95% in detecting sensitivity, specificity and number of oesphageal 
intubations from the data of the study done by Chou et al28. The incidence of 
oesophageal intubation was 5.6%. The overall accuracy of bedside upper airway 
ultrasonography was 98.1% (95% CI: 93.0% - 100.0%). The kappa value (Κ) was 
0.85, indicating a very good agreement between the bedside upper airway 
ultrasonography and waveform capnography. The sensitivity, specificity, positive 
predictive value and negative predictive value of bedside upper airway 
ultrasonography were 98.0% (95% CI: 93.0% - 99.8%), 100% (95% CI: 54.1% - 
100.0%), 100% (95% CI: 96.3% - 100.0%) and 75.0% (95% CI: 34.9% - 96.8%) 
respectively. The likelihood ratio of a positive test was infinite and the likelihood ratio 
of a negative test was 0.0198 (95% CI: 0.005 - 0.0781). The mean confirmation time 

27 
 
by ultrasound was 16.4 seconds. They concluded that ultrasonography could be used 
as an alternative of waveform capnography in confirming endotracheal tube 
placement in centres without capnography.  
 
Pfeiffer et al31 did a prospective, observational study in 2010 comparing the time 
taken by bilateral lung ultrasound (observing lung sliding) with auscultation and 
capnography for verifying endotracheal intubation. Two separate investigators, one 
reading the capnograph and the other performing ultrasound, were blinded from each 
other while performing endotracheal intubation in a patient inside an operating 
theatre. Both methods were thus used at once in a patient. Both methods correctly 
verified endotracheal tube placement in all 25 patients. Comparing ultrasound with 
the combination of auscultation and capnography, median time for ultrasound was 40 
seconds [Interquartile Range (IQR): 35 – 48 sec] vs. 48 seconds [IQR: 45 – 53 sec], 
p<0.0001. Mean difference was -7.1 sec in favour of ultrasound (95% CI: 9.4 - 4.8 
sec). Median time for auscultation alone was 42 sec [IQR: 37 – 47 sec], p= 0.6, with a 
mean difference of -0.88 sec in favor of ultrasound (95% CI: 4.2 – 2.5 sec). Thus they 
concluded that verification of endotracheal tube placement with ultrasound is as fast 
as auscultation alone and faster than the standard method of auscultation and 
capnography. 
 
Gottlieb et al32 conducted a blinded, randomized trial in 2014 designing a 4 step 
technique of using ultrasound to check endotracheal tube position in two human 
cadaver models, one thin and the other obese. The technique in short was a 
transtracheal ultrasound at the transcricothyroid level with the probe tilted 30 degrees 
towards the left from midline in horizontal view. They would shake the endotracheal 

28 
 
tube to see for artifact inside the trachea. If no tube was seen, the probe was moved to 
right of neck to see for similar artifact inside the oesophagus. Three ultrasound 
experts and 45 emergency medicine residents performed a total of 150 scans. Experts 
had a sensitivity of 100% (95% CI: 72% - 100%) and specificity of 100% (95%CI: 
77% - 100%) on thin cadaver, and a sensitivity of 93% (95% CI: 66% - 100%) and 
specificity of 100% (95% CI: 75% - 100%) on obese cadavers. Novice residents had a 
sensitivity of 91% (95% CI: 69% - 98%) and specificity of 96% (95% CI: 76% - 
100%) on thin, and a sensitivity of 100% (95% CI: 82% - 100%) specificity of 48% 
(95% CI: 27% - 69%) on obese cadavers. The overall mean time to detection was 17 
seconds (95% CI: 13 seconds to 20 seconds; range: 2 - 63 seconds) for experts and 29 
seconds (95% CI: 25 seconds to 33 seconds; range: 6 - 120 seconds) for residents. 
Their ultrasound technique was accurate and rapid for ultrasound experts. Among 
novices, their technique was accurate in thin, but less accurate in obese cadavers.32 
 
Two recent articles about ultrasound use during intubation for endotracheal tube 
position confirmation have been published in 2017. 
 
Nasreen et al33 did a study to determine the diagnostic accuracy of Tracheal Rapid 
Ultrasound Exam (TRUE) for detection of endotracheal tube placement. They used 
transverse suprasternal ultrasound method and verified tube position later with a 
lateral neck x-ray. Out of the 230 patients studied; the sensitivity, specificity, PPV, 
NPV and diagnostic accuracy of TRUE for detection of endotracheal tube placement 
taking lateral x-ray neck as gold standard were 98.80%, 95.24%, 98.21%, 96.77% and 
97.83% respectively.  
 

29 
 
Chintamani et al34 did a prospective, observational study was on 100 patients 
requiring tracheal intubation for general anaesthesia and used both capnography and 
transverse, suprasternal transtracheal static ultrasound after intubation to confirm the 
endotracheal tube placement. Ultrasound detected all five cases of oesophageal 
intubation, but could not detect five patients with correct tracheal intubation. 
Ultrasonography had a sensitivity of 96.84% (95% confidence interval [CI]: 94.25% - 
96.84%), specificity of 100% (95% CI: 50.6% – 100%), positive predictive value of 
100% (95% CI: 97.3% – 100%) and negative predictive value of 62.5% (95% CI: 
31.6% – 62.5%) when compared to capnography as the standard method for 
endotracheal tube confirmation. Kappa value was found to be 0.76, indicating a good 
agreement between ultrasonography and capnography for confirmation of 
endotracheal tube placement. Time taken for confirmation of endotracheal tube was 
8.989 ± 1.043 sec by capnography versus 12.0 ± 1.318 sec by ultrasound (p< 0.001). 
 
 
 
 
 
 
 
 
 
 

30 
 
OBJECTIVES 
 
General:  
To compare ultrasonography imaging and waveform capnography for 
endotracheal intubation confirmation in a tertiary hospital operating room 
setting. 
Specific: 
1. To determine the time taken by real-time ultrasonography imaging in detecting 
endotracheal tube placement. 
2. To determine the time taken by capnography waves in detecting endotracheal 
tube placement. 
3. To 
calculate 
the 
sensitivity 
and 
specificity 
of 
capnography 
and 
ultrasonography in detecting endotracheal tube placement.  
4.  To calculate positive and negative predictive values of these two methods in 
detecting endotracheal tube placement. 
5.  To interpret the degree of agreement of result obtained with ultrasonography 
and capnography using kappa statistics. 
 
 
 
 
 

31 
 
HYPOTHESIS 
 
Transtracheal ultrasonography and waveform capnography are both accurate 
methods of verifying endotracheal tube placement after intubation. 
Real-time transtracheal ultrasound is a faster method of detecting endotracheal tube 
placement compared to waveform capnography. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

32 
 
METHODOLOGY 
 
Study design 
Research Method: Qualitative and quantitative. 
Type of study: Prospective, observational. 
Study Population: Patients admitted for elective surgery at Tribhuvan University 
Teaching Hospital (TUTH) and Manmohan Cardiothoracic 
Vascular and Transplant Center (MCVTC) under general 
anaesthesia. 
Study site: Operating rooms, TUTH and MCVTC. 
 
Duration of study: 6 months. The study was conducted at MCVTC from January 17, 
2017 to April 14, 2017. It was continued at TUTH from April 15, 
2017 to July 14, 2074. 
Sampling Method:  Non-probability sampling. 
Sample size: Total 95 patients were taken for analysis. 
The formula for sample size with (1 -α)% confidence level and with maximum margin 
error of estimate of “d” for constructing confidence interval of true value of 
sensitivity or specificity using normal approximation is given as follows35: 
 

33 
 
Where 
 is pre-determined value of sensitivity or specificity that is ascertained by 
previous published data or clinician experience or judgment.35 
For α = 0.05, Zα/2 is inserted by 1.96.35,36 
Excerpted from the meta-analysis done by Chou et al6 where they found the 
sensitivity and specificity of  suprasternal transtracheal ultrasound for endotracheal 
tube confirmation to be 0.98 and 0.94 respectively, the specificity value for  
 in the 
equation was taken. Hence setting margin of error “d” at 5%, we could equate to: 
n = 1.962 x 0.94 x 0.06 / 0.052   = 86.66 
Adjusting for 10% drop outs and defaulters, a sample size of 95 was thus taken. 
Inclusion criteria: 
ASA I and II patients of both sexes above 16 years of age undergoing general 
anaesthesia with endotracheal tube placement. 
Exclusion criteria: 
- 
Patient refusal 
- 
ASA physical status III and above    
- 
History of prior difficult bag and mask ventilation or difficult intubation 
- 
History of prior oro-nasal or neck injuries, burns or scars 
- 
Active oral, pharyngeal or tracheal infection or inflammatory changes 
- 
Anticipated difficult airway or difficult intubation during preanaesthetic 
examination, with Mallampati grades II and above 
- 
Lung parenchymal and pleural diseases. Examples: asthma, COPD, 
bronchiectasis, reactive lung diseases, pneumonia, tuberculosis, pleural 
effusion, pneumothorax, lung or pleural malignancy etc. 
- 
Emergency surgery 

34 
 
- 
Patients with known oesophageal pathology. Examples: oesophageal 
carcinoma, stricture, tracheoesophageal fistula etc. 
- 
Full stomach or patients at risk of aspiration, e.g. pregnancy 
- 
Patients with a nasogastric tube in situ 
- 
NYHA grade 2 and above 
Materials and Methods 
The study was conducted inside the operating room no. 2 and 3 of MCVTC where 
capnography was available. These had Drager Fabius Plus, 2013 anaesthesia machine 
(ref: 8606800-48); Drager Infinity Delta, 2012 monitor (ref: MS18597); and Drager 
Scio Four, 2012 sidestream capnograph with capnometer (ref: 6871804), which had 
flow rate of 250ml/min and system response time of < 4 seconds. The ultrasound 
machine used in MCVTC was Sonosite M Turbo, 2013 (ref: P08189-83) made by 
Fujifilm Sonosite Inc. USA. 
The study was also conducted in operating rooms 1, 2 and 7 of TUTH. These had 
Drager Fabius Plus, 2013 anaesthesia machine (ref: 8606800-51). The monitor used in 
OT 1 and 2 was Nihon Kohden BSM-2301K, 2008 which had a mainstream 
capnometer with identification number TG-101T (2013). The monitor used in OT 7 
was Spacelabs Ultraview-SL 2700, 2013 which had a sidestream capnograph with 
identification number MDL-90499. The capnography module had sample line flow 
rate of 50ml/min ± 10ml/min and system response time of < 3 seconds. The 
ultrasound machine used was Sonosite M Turbo, 2015 (ref: P17000-15). 
Ethical approval from the Institutional Review Board (IRB) of Institute of Medicine 
(IOM) and the Department of Anaesthesiology, Maharajgunj Medical College (MMC) 
was obtained on January 16, 2017.  

35 
 
Eligible patients were evaluated one day prior to surgery. Written informed consent 
was taken (Appendix B). Patients were kept nil per oral at least 6 hours prior to 
surgery. Premedication with Tablet Diazepam 0.25mg/kg body weight per oral was 
given on the evening before and the morning of surgery. 
Intravenous line was opened with a 18 Gauge Cannula in the non-dominant hand in 
the operation theatre (OT) recovery area. Patient was given 0.025 mg/kg of Injection 
Midazolam prior to shifting to the operating room. Baseline vital parameters: NIBP, 
heart rate and SPO2 were recorded at the OT recovery by the researcher. 
The personnel involved in this study were: 
1. 
Ultrasound machine operator: was an anaesthesia faculty who had good 
understanding of using the ultrasound machine and had previously done at 
least 10 tracheal ultrasonography during intubation. 
2. 
Airway management/ Intubation: was done by a second or third year 
anaesthesia resident. 
3. 
Supervising anaesthesia faculty: who supervised the airway management and 
intubation. 
4. 
Anaesthesia resident or an anaesthesia assistant: injected drugs for induction 
of anaesthesia and watched the capnogram in monitor. 
5. 
Researcher: noted down the time taken for confirmation by both methods. 
Also inspected for changes in vitals that would exclude the participant out of 
the study. 
Inside the operating room the ultrasound machine was kept on the left hand side and 
in line with pelvis of the patient. The ultrasound operator was on the right hand side 
of the patient and in line with patient’s xiphisternum. The blinding was done such that 

36 
 
the person reading capnogram would face away from the ultrasound machine, and the 
ultrasound operator would be facing away from the capnograph monitor. 
Patient was placed supine comfortably in the operating table. Continuous ECG and 
SPO2 monitoring, 5 minute interval NIBP monitoring or continuous invasive blood 
pressure monitoring when available was done. A running intravenous drip of 
crystalloid solution; Ringer’s Lactate, Normal saline or Plasmalyte as required was 
started. Injection Fentanyl 2 microgram per kg was given intravenously. Then 
Injection Propofol 2 milligram per kg was given intravenously in TUTH and non-
cardiac surgery patients in MCVTC, and Injection Etomidate 0.3mg per kg 
intravenously was given to cardiac surgery patients in MCVTC for induction. 
Induction of anaesthesia was complete after patient became unresponsive with central 
mid-dilated pupil and absence of eye lash reflex. 
Manual bag and mask ventilation adequacy was then checked. Injection Vecuronium 
0.1 milligram per kg was given intravenously, and the stopwatch was started. Manual 
bag and mask ventilation was continued by the primary intubating resident and 
assisted by the supervising anaesthesia faculty as needed. 
High frequency linear ultrasound probe, 9-13 Megahertz, was placed transversely just 
above the suprasternal notch. The probe was shifted slightly cranially or caudally as 
needed to obtain the best visualization of trachea and oesophagus in the same image. 
After 5 minutes of injecting Vecuronium, the researcher reset his stopwatch and 
announced “start” loudly (start point). Laryngoscopy and tracheal intubation was done 
by the anaesthesia resident. The ultrasound operator held the probe in the appropriate 
place as previously determined. If the position of the probe obstructed laryngoscopy, 

37 
 
the probe was shifted caudally and tilted slightly cranially. The study was continued 
only if the latter ultrasound image could also visualize both trachea and oesophagus.  
After intubation, the anaesthesia machine which was preset in volume control mode 
with tidal volume of 6ml/kg, respiratory rate of 26 breaths per minute (as used by 
Pfeiffer et al31 in their study), PEEP zero and inspiration:expiration ratio of 1:2; was 
then attached to the endotracheal tube via the anaesthesia machine circuit with ETCO2 
probe connected at the angle piece of the patient end of the circuit.  
The ultrasound operator announced loudly as either “ultrasound positive” for tracheal 
intubation result, or “ultrasound negative” for oesophageal intubation result. The 
researcher noted down the time in the data entry proforma sheet (end point for 
ultrasonography).  
The next anaesthesia resident (or anaesthesia assistant) meanwhile watched over the 
capnogram in the monitor. After 6 mechanical ventilations, he announced loudly as 
“capnograph positive” for tracheal intubation result, or “capnograph negative” for 
oesophageal intubation result. The researcher noted down the time in data entry 
proforma sheet (end point for capnography). 
The supervising anaesthesia faculty then auscultated the chest in 5 areas in the order: 
right supramammary – left supramammary - left axillary – right axillary – 
epigastrium. The ultrasound operator performed bilateral lung ultrasound in second 
intercostal spaces in the mid-clavicular line and observed for lung sliding. The final 
endotracheal tube position in trachea was confirmed when there was presence of 
bilateral air entry on auscultation and lung sliding on ultrasound. In case of only 
unilateral air entry and unilateral lung sliding, the endotracheal tube was readjusted 

38 
 
for endobronchial intubation and reconfirmed again; the subject was not excluded 
from the study in the event of endobronchial intubation. 
If there was absence of breath sounds with absence of lung sliding and bar-code sign20 
in the ultrasound in bilateral chest regions, reconfirmation further was done by the 
supervising anaesthesia faculty by performing repeat laryngoscopy and visualizing the 
position of endotracheal tube in relation to the vocal cords. This repeat reconfirmation 
was done because post-intubation bronchospasm or mucous plugging could also 
present with similar auscultation and lung ultrasound finding and thus negate the 
validity of the study. The supervising anaesthesia faculty would then reintubate 
himself if tube position in the oesophagus was seen during repeat laryngoscopy. The 
second intubation was not accounted for in this study. 
Participants were also excluded if there was: 
• Unanticipated difficult bag and mask ventilation 
• Unanticipated difficult intubation or CL grade 3 and 4 cases, use of bougie for 
intubation. 
• Fall in Spo2 (< 90%) before endotracheal tube position confirmation 
• Bradycardia (heart rate < 40 beats/min ) or hypotension (mean arterial 
pressure < 60 mm of Hg, systolic blood pressure < 80 mm of Hg) during or 
prior to intubation 
• Tachycardia more than 120 bpm or blood pressure more than 180 mm Hg 
systolic or 110 mm Hg diastolic during or prior to intubation 
There were 36 participants enrolled at MCVTC, out of which 5 of the participants had 
to be excluded out of the study. One had unanticipated difficult intubation, and the 
other four had hypotension after induction of anaesthesia. There were 67 participants 

39 
 
enrolled at TUTH, out of which 3 participants had to be excluded out of the study. 
Two subjects had hypotension after induction of anaesthesia. The other one had to be 
excluded because the ultrasound machine went into hung state. Thus there were 31 
subjects from MCVTC and 64 subjects from TUTH. Data collection was terminated 
once the sample size of 95 was met. Different individuals operated ultrasound on the 
subjects in this study. Flow diagram of the study is shown in figure 8. 
Operational Definitions 
Ultrasound positive: meant ultrasound detected tracheal intubation. There was 
fluttering and movement inside the tracheal acoustic shadow as the endotracheal tube 
was passed, and by the completion of intubation there was only one comet tail 
appearing acoustic shadow. Color Doppler ray showed color change inside the 
acoustic shadow on shaking the endotracheal tube. 
Ultrasound negative: meant ultrasound detected oesophageal intubation. There was 
fluttering and increase in echogenicity in the region of oesophagus as the endotracheal 
tube was passed. By the completion of intubation, there were two comet tail appearing 
acoustic shadows, “double-tract sign”. Color Doppler ray was seen outside the trachea 
on shaking the endotracheal tube. 
Capnograph positive: meant capnogram showed regular normal shaped waveforms 
after 6 ventilations. The outcome was tracheal intubation. 
Capnograph negative: meant oesophageal intubation. The capnogram had no 
waveforms or irregular, bizarre or non-uniform shaped waveforms after 6 ventilations. 
After confirmation of the endotracheal tube position, true and false positives and 
negatives were determined for both the methods as depicted in table 1. 

40 
 
Sensitivity, specificity, positive predictive value and negative predictive value, 
likelihood ratios; for both ultrasonography and capnography were calculated using 
their corresponding formulas.37 The results were extrapolated into confidence 
intervals using Clopper-Pearson confidence interval.37 
 
 
Table 1. Designation of true and false positives and negatives. 
 
Capnography 
Ultrasonography 
Tracheal 
outcome 
Oesophageal 
outcome 
Tracheal outcome 
Oesophageal 
outcome 
True positive 
(TP): final 
position in 
trachea. 
True negative 
(TN): final position 
in oesophagus. 
True positive 
(TP): final 
position in 
trachea. 
True negative (TN): 
final position in 
oesophagus. 
False positive 
(FP):  final 
position in 
oesophagus. 
False negative 
(FN): final position 
in trachea. 
False positive 
(FP) : final 
position in 
oesophagus. 
False negative (FN): 
final position in 
trachea. 
 
Sensitivity = TP / (TP+FN). 
Specificity = TN / (TN+FP). 
Positive predictive value (PPV) = TP / (TP+FP). 
Negative predictive value (NPV) = TN / (TN+FN). 
Confidence intervals, CI (at 95 % level of confidence): for example for sensitivity                             
CI = (Sensitivity + 1.96SE, sensitivity – 1.96SE).      Where  SE is standard error, 
SE for sensitivity = square root of [ sensitivity (1 – sensitivity)/( TP+FN)]37 
 

41 
 
Accuracy = (TP+TN) / (TP+TN+FP+FN). 
(TP=True Positive, TN=True Negative, FP=False Positive, FN= False Negative) 
Likelihood ratio of a positive test: was given by 
 
The positive likelihood ratio values corresponded to different probabilities as 
follows37: 
Table 2. Interpretation of positive likelihood ratio.37 
Positive likelihood ratio value 
Probability 
0 
Excluded disease. 
> 10 
Large change in likelihood (or in other words high 
probability of any individual having a positive result 
on using the diagnostic test). 
5 – 10 
Moderate change in likelihood. 
2 – 5 
Small change in likelihood. 
1 
No change. 
 
 
Likelihood ratio of negative test: was given by 
 
 

42 
 
The negative likelihood ratio values also corresponded to different probabilities as 
follows37: 
Table 3. Interpretation of negative likelihood ratio.37 
Negative likelihood ratio value 
Probability 
infinity 
Excluded normality. 
< 0.1 
Large change in likelihood (or in other words high 
probability of any individual having a negative 
result on using the diagnostic test). 
0.1 – 0.2 
Moderate change in likelihood. 
0.2 – 0.5 
Small change in likelihood. 
1 
No change. 
 
Data collection and management 
The Pre-anaesthetic (PAC) form of the Department of Anaesthesiology, MMC, IOM; 
(Appendix A) was used to evaluate patients for inclusion into the study. All 
participants’ data such as gender, age, ethnicity, diagnosis, BMI, weight, ASA status, 
medical comorbidities, airway examination was collected on data entry proforma 
sheet (Appendix C). The proforma sheet also recorded the baseline vitals and the 
vitals after induction of anaesthesia and after intubation. The results for 
ultrasonography and capnography, the respective time taken to obtain the results were 
recorded in the proforma sheet. 
Data entry was done into Microsoft excel 2010. (Appendix E) 
 

43 
 
Statistical Analysis 
Descriptive variables were expressed as mean ± standard deviation, median, range, 
interquartile range, frequency, percentage and proportion. The calculations were done 
in Microsoft excel 2010. 
The sensitivity, specificity, positive and negative predictive values, accuracy, along 
with their confidence intervals and likelihood ratios for positive and negative results 
were calculated by defining the respective mathematical functions into Microsoft 
excel 2010. 
The mean and median times along with the interquartile range and standard 
deviations, taken for confirmation by capnography and ultrasonography were 
calculated using SPSS 23.0. Difference in time was calculated as method 1 
(ultrasonography) minus method 2 (capnography) and reported as mean with 95% 
confidence interval; the results were compared using paired student t-test with p 
values at 95 % level of significance. The analysis was done using SPSS 23.0. 
Kappa statistic was used to see agreement over and above that which would have 
occurred just by chance between these two methods. The kappa (ƙ) value was 
calculated using SPSS 23.0. It was interpreted based on the following criteria38: 
Table 4. Intepretation of kappa value.38 
    Kappa value (ƙ) 
Degree of agreement 
0.81 - 1.00 
Very good. 
0.61 - 0.80 
Good. 
0.41 - 0.60 
Moderate. 
0.21 - 0.40 
Fair. 
<0.20 
Poor. 
 

44 
 
 
 
 
 
 
 
 
 
 
          Method 1. Ultrasonography                            Method 2. Capnography 
 
 
 
                     (Reconfirmation)        
                                                                                                                
                                                                                                                                   
                                                                                                      
 
 
 
 
 
 
 
 
 
 
Assessed for eligibility (n=103) 
Excluded  (n=8) 
• 1 unanticipated difficult    
intubation 
• 6 hypotension after 
induction of anaesthesia 
• 1 ultrasound machine 
malfunction 
Studied patients (n=95) 
• 
Sensitivity, Specificity, Positive predictive value (PPV), Negative 
predictive value (NPV), Positive likelihood ratio (LR+ ), Negative 
likelihood (LR-), Accuracy.  
• 
Time taken for confirmation, Difference in time (Method 1 – Method 2). 
Trachea 
(n=81) 
Oesophagus 
(n=14) 
Trachea    
(n=83) 
Oesophagus 
(n=12) 
Oesophagus 
(n=1)        
FP 
Trachea 
(n=82)     
TP
Trachea 
(n=2)   
FN
Oesophagus 
(n=10)      
TN 
Trachea 
(n=81)    
TP    
Oesophagus 
(n=0)       
FP 
Trachea 
(n=3)  
FN   
Oesophagus 
(n=11)    
TN 
Analysis 
Reconfirmation 
Fig. 8. Study flow diagram. 
(TP=True Positive, FP=False Positive, TN=True Negative, FN=False Negative) 

45 
 
RESULTS 
Descriptive data 
Demography 
Among the 95 subjects, the mean age was found out to be 44.24 years with standard 
deviation of ± 16.18 years, and the median age was 47 years. The youngest patient 
was of 16 years, and the eldest patient was 85 years old. Most patients were in the age 
group of 41 to 50 years. 
Table 5. Demographic profile according to age. 
Mean ± SD (in yrs) 
Median (in yrs) 
Maximum (in yrs) 
Minimum (in yrs) 
44.24 ± 16.18 
47 
85 
16 
 (n=number, SD= Standard Deviation, yrs = years) 
 
Fig. 9. Distribution of the subjects into different age groups. 
11
12
18
21
18
15
0
5
10
15
20
25
15-20 yrs
21-30 yrs
31-40 yrs
41-50 yrs
51-60 yrs
Above 60 yrs
No. of patients
Age in years
Patients distributed into different age groups

46 
 
Among the 95 subjects, there were 51 females (53.68%) and 44 males (46.32%) in 
this study. 
 
Fig. 10. Sex-wise profile of patients in the study. 
The majority of patients were Brahmins (40%), followed by Chhetris (22.10%), 
Newars (14.70%), Magars (7.36%), and others (15.84%);  as shown in figure 11. 
Others include Rai (4), Bhaisnav (1), Chaudhary (1), Muslim communities (2), Lama 
(2), Gurung (1), Damai (1), Tamang (2), Thakuri (1) and Sherpa (1). 
BMI 
The mean body mass index (BMI) of the 95 patients was found to be 23.55 ± 3.58 
(mean ± standard deviation); the median BMI was 23.72 and the inter-quartile range 
[20.68 - 25.92], all values expressed in kg/m2. The summary is shown in table 3 and 
figure 12.  
 
44
51
Sex-wise distribution of patients
Males
Females

47 
 
 
Fig. 11. Distribution of patients as per ethnicity in this study. 
 
Table 6. Average body mass index (BMI) of patients. 
 
Mean ± SD 
Range 
Median 
IQR 
BMI (kg/m2) 
23.55 ± 3.58 
16.33 - 33.88 
23.72 
[20.68 - 25.92] 
 
(SD = Standard Deviation, Range = Maximum - minimum values; IQR = Interquartile range) 
 
 
Fig. 12. Frequency of patients according to WHO classification of BMI. 
 
 
Ethnicity
Brahmin (40%)
Chhetri (22.10%)
Newar (14.73%)
Magar (7.36%)
Others (15.84%)
6
56
31
2
0
10
20
30
40
50
60
16-18.5 (underweight)
18.5-25 (normal)
25-30 (overweight)
30-35 (moderately
obese)
No. of patients
Body Mass Index in kg/m2 (WHO classification)
BMI

48 
 
ASA Physical Status 
There were 46 ASA I patients and 49 ASA II patients in this study. The clinical 
conditions in patients with ASA II status are listed below in table 4. Table 4 does not 
account for the presence of multiple clinical conditions in the patients. 
 
Fig. 13. ASA Physical status distribution of patients. 
Table 7. Clinical conditions in ASA II patients. 
 
No. of patients 
MCTVC 
TUTH 
Valvular heart disease 
8 
0 
Coronary heart disease 
14 
1 
Vascular disease 
6 
0 
Hypertension 
14 
6 
Diabetes Mellitus 
4 
1 
Hypothyroidism 
3 
3 
Hepatitis C positive  
0 
1 
Central nervous system disease 
0 
8 
 
46
49
0
10
20
30
40
50
ASA I
ASA II
No. of patients
ASA physical status comparison

49 
 
Analytical Statistics and Data 
Out of the total 95 intubations, there were 11 oesophageal intubations. The incidence 
of oesophageal intubation was 11.57% in this study.  
Ultrasonography 
Ultrasound falsely detected one oesophageal intubation as tracheal, and two tracheal 
intubations as oesophageal. 
Table 8. Distribution of positives and negatives for ultrasonography. 
 
Position showed by 
Ultrasound  
Endotracheal tube position confirmation 
 
Total 
Trachea 
Oesophagus 
Trachea (n) 
TP = 82 
FP = 1 
83 
Oesophagus (n) 
FN = 2 
TN = 10 
12 
Total 
84 
11 
n = 95 
 
(n=no. of patients, TP=True Positives, FP=False Positives, FN=False Negatives, TN=True 
Negatives) 
 
The sensitivity, specificity, positive predictive value and negative predictive value 
(with their corresponding 95% confidence intervals in round brackets) were calculated 
to be 97.62% (91.66% - 99.71%), 90.91% (58.72% - 99.77%), 98.80% (92.67% - 
99.81%) and 83.33% (55.66% - 95.22%) respectively. The positive likelihood ratio 
was 10.74, which suggested a large change in the likelihood of positive result. The 
negative likelihood ratio was 0.03 which also suggested a large change in the 
likelihood of negative result. The accuracy of ultrasonography in confirming 
endotracheal tube placement was 96.84% (92.92% - 100%). 

50 
 
 
Fig. 14. Distribution of positives and negatives for ultrasonography. 
Capnography 
There were three false negative results given by waveform capnography. There was 
no false positive result. 
Table 9. Distribution of positives and negatives for capnography. 
Position showed by 
waveform capnography 
Endotracheal tube position confirmation 
 
Total 
Trachea 
Oesophagus 
Trachea (n) 
TP = 81 
FP = 0 
81 
Oesophagus (n) 
FN = 3 
TN = 11 
14 
  Total 
84 
11 
n=95 
(n=no. of patients, TP=True Positives, FP=False Positives, FN=False Negatives, TN=True 
Negatives) 
0
10
20
30
40
50
60
70
80
90
Trachea
Oesophagus
TP = 82
FN=2
FP=1
TN=10
No. of patients
Endotracheal tube position after confirmation
ET tube position
shown by USG
Trachea
Oesophagus

51 
 
 
Fig. 15. Distribution of positives and negatives for capnography. 
 
The sensitivity, specificity, positive predictive value and negative predictive value 
(with their corresponding 95% confidence intervals in round brackets) of capnography 
were calculated to be 96.43% (89.92% - 99.26%), 100% (71.51% - 100%), 100% 
(100% - 100%) and 78.57% (54.69% - 91.76%) respectively. The positive likelihood 
ratio was infinity. The negative likelihood ratio was 0.04 which suggested a large 
change in the likelihood of negative result. The accuracy of capnography in 
confirming endotracheal tube placement was 96.84% (92.92% - 100%). 
Both ultrasonography and waveform capnography were found to be good, reliable and 
fairly accurate diagnostic methods of confirming endotracheal tube position. 
Ultrasonography was comparable diagnostically with capnography for endotracheal 
tube confirmation. The comparisons of the pretest and posttest probabilities of the two 
methods are shown in table 10. 
 
0
10
20
30
40
50
60
70
80
90
Trachea
Oesophagus
TP=81
FN=3
FP=0
TN=11
No. of patients
Endotracheal tube position after confirmation
ET tube position 
shown by 
capnography
Trachea
Oesophagus

52 
 
Table 10. Comparison of the diagnostic characteristics of ultrasonography and 
waveform capnography. 
 
Ultrasonogrpahy 
Waveform 
Capnogrpahy 
Sensitivity in % (95% CI) 
97.62 (91.66- 99.71) 
96.43 (89.92 - 99.26) 
Specificity in % (95% CI) 
90.91 (58.72 - 99.77) 
100 (71.51 - 100) 
PPV in % (95% CI) 
98.80 (92.67- 99.81)  
100 (100 – 100)  
NPV in % (95% CI) 
83.33 (55.66 - 95.22) 
78.57 (54.69 - 91.76) 
Accuracy in % (95% CI) 
96.84 (92.92 - 100) 
96.84 (92.92 - 100) 
Positive likelihood ratio 
10.74 
Infinity 
Negative likelihood ratio 
0.03 
0.04 
 
(CI= Confidence Interval, PPV= Positive Predictive Value, NPV= Negative Predictive Value) 
 
Both ultrasonography and capnography together had correctly identified 10 out of the 
11 oesophageal intubations. The 84 tracheal intubations were correctly identified by 
both ultrasonography and capnography or either one of these methods. Using the 
same formula (page 35), the combined accuracy of both the methods together was 
98.94% (94 divided by 95, in percentage). 
The analysis of agreement between the ultrasonography and capnography results was 
done using Cohen’s kappa statistics. A kappa value of 0.749 with 95% confidence 
interval of (0.567 – 0.931) and standard error of 0.093 was found. The kappa value 
therefore showed a good agreement between the result of these two methods. 
 
 

53 
 
Time taken for endotracheal tube confirmation 
Real-time ultrasonography was faster than waveform capnography for endotracheal 
tube confirmation in all cases. The mean time for confirmation by ultrasonography 
was 26.79 ± 7.64 seconds (mean ± standard deviation). The mean time for 
confirmation by capnography was 43.03 ± 8.71 seconds.  
The mean difference in time was 16.36 seconds (95% CI: 15.70sec – 17.02 sec). The 
median difference in time was 16 seconds. The standard deviation in difference in 
time was 3.23 seconds. The standard error of mean (SEM) was 0.332 seconds. The 
difference in time was highly significant (p = 0.011). 
Table 11. Time taken for endotracheal tube confirmation. 
 
Range 
(in 
seconds) 
Mean ± SD 
(in seconds) 
Median 
(in 
seconds) 
IQR (in 
seconds) 
p-value 
Time taken by 
ultrasonography 
14 - 50 
26.79 ±7.64 
26.00 
[15 - 37] 
 
Time taken by 
capnography 
27 - 67 
43.03 ±8.71 
42.00 
[29 - 55] 
 
Difference in time     
(ultrasonography -
capnography) 
9 - 24 
16.36 ±3.23 
16.00 
 
0.011 
(SD = Standard Deviation, IQR = Inter-Quartile Range, Range = Maximum-minimum values) 
A subgroup analysis was done to test whether the time delay in sidestream 
capnograph could have affected the p-value obtained in difference in time. Two 
subgroups were divided: one subgroup in which sidestream capnography was used, 
and the other subgroup in which mainstream capnography was used. There were 37 
patients in the mainstream subgroup and 58 patients in the sidestream subgroup. The 
median time for confirmation of endotracheal tube position in mainstream subgroup 
was 37 seconds. The median time for confirmation of endotracheal tube position for 

54 
 
capnography in sidestream subgroup was 45.5 seconds. The findings of difference in 
time between ultrasonography and capnography methods in these subgroups are 
summarized in table 12. 
Table 12. Subgroup analysis for difference in time taken for endotracheal tube 
confirmation. 
Difference in time     
(ultrasonography-capnography) 
Range (in 
seconds) 
Mean ± SD 
(in seconds) 
Median (in 
seconds) 
p-value 
Mainstream subgroup (n=37) 
9 - 19 
14 ± 2.62 
 
14 
p < 0.01 
Sidestream subgroup (n=58) 
12 - 24 
17.87 ± 2.64 
17.50 
p < 0.01 
 
(SD = Standard Deviation, Range = Maximum - minimum values) 
The distribution was found to be normal in both subgroups on applying Shapiro-Wilk 
test (p < 0.01). Student’s t- test was used to determine the p-value of difference in 
time to confirm endotracheal tube position between the two subgroups. The p-value, 
p< 0.01 was obtained in both the subgroups, which meant that use of sidestream 
capnography with a delay time did not affect the significant difference in time 
between ultrasonography and capnography found in this study. 
 
 
 
 

55 
 
DISCUSSION 
Both ultrasonography and waveform capnography were found to be reliable and 
accurate methods of confirming endotracheal tube position in this study. The variables 
that were studied and analyzed in this study are now discussed further.  
Descriptive data  
The results of this study were not affected by the demographic and physical health 
profiles of the subjects. 
In this study, the patients that were included had ages ranging from 16 to 85 years. 
Most patients were between 41 to 50 years of age. The median age of the patients was 
47 years. There were more females than males in this study, male: female ratio being 
44:51 (or 1:1.16). 
Elderly patients could have calcifications in thyroid cartilage and trachea, and females 
could have large thyroid glands which could create artifacts and unclear acoustic 
shadow in neck ultrasound.18,20 However external neck examination and chest x-ray 
assessment of lower neck when available had been done during pre-anaesthetic check-
up. Before laryngoscopy was done, the ultrasound probe had examined the lower 
anterior neck for the best view for the study during which these conditions were ruled 
out. Thus, the demographic profile did not affect the outcomes of this study. 
According to the WHO classification for body mass index (BMI), 31 out of the 95 
patients (32.63%) in this study were overweight and 2 patients (2.1%) were morbidly 
obese. Obesity can lead to thick neck with increased fatty soft tissue mass and edema 
within the airway, which can create unclear acoustic image. However patients with 

56 
 
anticipated difficult airway were not included in this study. Pre-anaesthetic (PAC) 
examination excluded patients with mouth opening less than three finger breadths of 
the patient, restricted temporo-mandibular joint movement, stiff cervical neck flexion 
and extension movements, Mallampati grades II and above, mobile teeth, edentulous 
upper or lower jaw, upper lip bite test grade III, thyromental distance < 6.5 cms, 
thyromental height < 3 finger breadths of the patient and neck circumference > 40 
cms.  
Though there were more ASA II patients than ASA I, the ASA physical status 
classification did not affect the objectives of this study because any clinical condition 
that could affect the outcome of the study had already been previously excluded. 
Clinical conditions that could lead to hypoxemia or change in the exhaled CO2 levels 
from the lungs, for example obstructive or restrictive airway diseases, pneumothorax, 
pleural effusion, malignancy had been excluded. 
Hence these descriptive variables did not affect the outcome of the study. These 
variables reflect the demographic profile of the patients served at the academic centres 
of IOM in Maharajgunj and provide validity to the study. This data could help as 
reference for researchers who might carry out similar studies in the same centres in 
future. 
Analytical Statistics 
The incidence of oesophageal intubation was 11.57% in this study. Reported 
incidence of oesophageal intubations during elective intubation is less than 2%.12,39 
The incidence of oesophageal intubation increases up to 6 - 16 % during in-hospital 
emergency intubations.29,30,39,40  

57 
 
Ultrasonography 
In this study, the sensitivity, specificity, positive predictive value and negative 
predictive value (with their corresponding 95% confidence intervals) of 
ultrasonography were calculated to be 97.62% (91.66% - 99.71%), 90.91% (58.72% - 
99.77%), 98.80% (92.67% - 99.81%) and 83.33% (55.66% - 95.22%) respectively. 
The sensitivity of ultrasonography in this study is comparable to sensitivity reported 
in the meta-analyses done by Das et al21 and Chou et al6, which were 98% and 93% 
respectively. The specificity was 90.91% in this study, which is slightly lower 
compared to the above mentioned meta-analyses where specificity ranges from 97 to 
98%.6,21 But the 95% confidence interval of specificity in this study extends from 
58.72 to 99.77% which covers the reported specificity 97 to 98% in these meta-
analyses. Thus the calculated pretest probabilities of ultrasonography in this study 
were not different from those reported in literature. 
The PPV and NPV of ultrasonography calculated in this study were 98.8% and 
83.33% respectively. The PPV of ultrasonography in this study is similar to that found 
by Adi et al30, Chou et al28, Chintamani et al34 and Nasreen et al33: the reported PPV 
ranges from 98 to 100% in these studies. The NPV of ultrasonography has been 
reported to be: 62.5% by Chintamani et al34, 75% by Adi et al30, 94% by Chou et al28, 
and 96.77% by Nasreen et al33. The 95% confidence interval of NPV of 
ultrasonography in this study was (55.66%- 95.22%), which is comparable to the 
NPV found by the above mentioned studies. 
Ultrasonography had an accuracy of 96.84% in endotracheal tube confirmation in this 
study. Similar accuracy ranging from 97 to 98% had also been found by previous 
researchers.28,30,33 

58 
 
There are various ways of using ultrasonography for endotracheal tube confirmation. 
At the level of vocal cords, the fluttering of vocalis ligament or a change in the 
position of vocal cords can be observed as the endotracheal tube passes through. But 
this method was found to be less accurate by Singh et al41, the accuracy of this 
technique was 71% in their study. 
Dynamic real-time as well as static ultrasound can be done at the level of 
transcricothyroid membrane and the suprasternal area for endotracheal tube 
confirmation. Most studies have used static ultrasound after passing the endotracheal 
tube due to the argument that the ultrasound probe position interferes with the act of 
laryngoscopy.28,30 This could be more true for transcricothyroid ultrasonography 
because of the more cranial location of the probe. But tilting the probe can mitigate 
the matter provided that the new image shows the desired structures clearly as well.  
Real-time ultrasound has been found to be very effective and rarely hampering the 
process of intubation using laryngoscopy. In the meta-analysis done by Chou et al6, 
tracheal ultrasonography performed in real-time was associated with superior 
sensitivity (0.94, 95% CI: 0.86 – 0.98) than that performed in a static (post-intubation) 
manner (0.91, 95% CI: 0.70 – 0.98). Werner et al42 did a pilot study and found the 
sensitivity and specificity of real-time ultrasound at suprasternal level in cadavers to 
be both 100%. Similar type of study done by Karacebay et al27 in patients during 
emergency intubation yielded high sensitivity and specificity of real-time 
transtracheal suprasternal ultrasound, the results being 97% and 88% respectively. 
Milling et al43 found the specificity and sensitivity of real-time transcricothyroid 
ultrasound to be 100% and 97% respectively. Ma et al44 did both real-time and static 
post-intubation ultrasound examination at transcricothyroid level to check 
endotracheal tube position in human cadavers and they found that diagnostic 

59 
 
reliability of real-time ultrasound to be better than that of static evaluation; sensitivity 
and specificity of real-time ultrasound was 97% and 100% respectively, compared to 
51% and 91% for static ultrasound.  
Similarly good diagnostic accuracy and reliability have been found with static 
ultrasound in human subjects during emergency intubations. Adi et al30 used 
transcricothyroid ultrasound in longitudinal or transverse probe position as 
appropriate after emergency intubation and Chou et al28 used transverse suprasternal 
static ultrasound after intubation to confirm endotracheal tube position in their studies. 
Both techniques were found to be accurate and reliable. 
Lung ultrasound to see for lung sliding can also be used to confirm endotracheal tube 
position. Weaver et al45 found this method to be accurate with results similar to 
transtracheal ultrasound methods in detecting endotracheal tube position in cadavers. 
Pfeiffer et al31 found this method to be accurate and reliable in anaesthesized patients 
in an operating room. 
Real-time suprasternal transtracheal ultrasonography in transverse orientation was 
used in this study. For reconfirmation of endotracheal tube position we used 
auscultation along with lung sliding since auscultation alone is not a reliable method 
of endotracheal tube confirmation.3,26,46 However, if there was absence of breath 
sounds with absence of lung sliding in bilateral chest regions, another reconfirmation 
was done by performing repeat laryngoscopy and visualizing the position of 
endotracheal tube passing through the vocal cords. This reconfirmation was done 
because post-intubation bronchospasm or mucous plug could also present with similar 
auscultation and lung ultrasound finding. Direct visualization is also regarded to be 
gold standard by few authors.3,4 On reconfirmation if endotracheal tube position was 

60 
 
tracheal, repeat laryngoscopy was not done considering the possibility of airway 
trauma on repeat manipulation. 
There were two false negative and one false positive result with ultrasonography. In 
case of one of the false negatives, the ultrasound operator had to adjust the probe 
position because the intubating resident was having difficulty in doing laryngoscopy 
due to interference by the ultrasound probe. However, the latter ultrasound image had 
clearly showed both tracheal acoustic shadow and oesophageal oval shaped 
hyperechocity. Ultrasound probe adjustment had to be done in 5 other cases as well, 
all of whom in which ultrasound had produced true results anyway. So ultrasound 
probe adjustment itself was unlikely to have caused false result in this case.  
In both false negative cases, the acoustic shadow post intubation was unclear and 
seemed to have two different artifacts; the color Doppler ray was seen between the 
two artifacts. Such artifacts might have been caused by calcifications in the thyroid 
gland or tracheal cartilages and soft tissues.18 The artifacts might also have been 
caused by reverberations produced by particulate matter like dirt or sand between the 
probe and skin. Subcutaneous emphysema can also produce artifacts.18 However, all 
these factors had been well accounted for. An uncontaminated ultrasound jelly was 
used to get a uniform thick layer over the probe to maximize probe to skin contact via 
the gel medium. The ultrasound probe had scanned the lower anterior area of neck 
before laryngoscopy to rule out calcifications, masses, emphysema etc. 
In case of the false positive result, the acoustic shadow had become unclear after 
intubation but had not widened. The color Doppler ray appeared inside the acoustic 
shadow on shaking the endotracheal tube. There had been no need for adjustment of 
the ultrasound probe position in case of the false positive subject. This false result 

61 
 
might have occurred due to the cervical spine movement during laryngoscopy 
rendering the oesophagus to lie just posterior to the trachea instead of posterolateral 
relation, thus rendering only a single acoustic shadow.17 
A large change in likelihood for either a positive or a negative result meant that for 
any individual, the probability of the endotracheal tube being in the trachea was very 
high if ultrasound showed tracheal intubation. And the probability of the endotracheal 
tube being in the oesophagus was very high if ultrasound showed oesophageal 
intubation. 
The average time taken by ultrasonography for assessment of endotracheal tube 
position in this study was 26.79 ± 7.64 (mean ± SD) seconds.  
As different individuals performed ultrasonography in this study, variations in time 
taken for endotracheal tube confirmation by ultrasonography occurred due to inter-
operator differences as well. 
The median operating time of static post-intubation ultrasound was found to be 9 
seconds with IQR [6 – 14 sec] by Chou et al28 in their study. This was significantly 
faster than transcricothyroid static ultrasound for endotracheal tube confirmation done 
by Adi et al30; their median time was 16.40 seconds. The results of these studies 
cannot be compared with this study because the beginning of laryngoscopy was taken 
as the start point for time assessment in this study. These studies started their 
assessment after intubation. The time for laryngoscopy is directly operator dependent 
and thus the time taken for assessment of endotracheal tube position directly increases 
with more time spent on doing laryngoscopy and intubation in this study.  
 

62 
 
Capnography 
The sensitivity and specificity of capnography to detect endotracheal tube position 
was found to be 96.43% and 100% respectively in this study. This was similar to 
aggregate sensitivity and specificity of 93% and 97% found by Li in his meta-
analysis.24 This meta-analysis included trials which used any form of end tidal CO2 
detection device in adult human subjects. We have used only waveform capnography 
which is the gold standard; colorimetric and quantitative ETCO2 are less accurate than 
waveform capnography.3,7,8,12 
There were three false negative results in capnography. Two of the three false 
negative results occurred while using sidestream capnography at TUTH and the other 
false negative result occurred at MCVTC which also had sidestream capnography. 
There were more than two irregular waveforms during the first six ventilations in 
these false negative cases.  
The false negatives might have occurred in the sidestream capnographs because these 
are more likely to be blocked due to fogging or misting2,7 such that the sampling line 
gas flow could have been obstructed. At MCVTC, after about 15 irregular waveforms, 
there was no waveform seen for about the next 90 seconds followed by presence of 
regular waveforms thereafter. This might be due to auto calibration of the capnograph, 
the occurrence of which during intubation might have produced false negative result.  
Other causes like compromised pulmonary blood flow and bronchospasm can also 
lead to false negative results.3,9,10 Patients who had hypotension after induction of 
anaesthesia that could lead to compromised pulmonary flow, were excluded from this 
study. Bronchospasm would be identified by auscultation or high peak airway 

63 
 
pressure displayed in the ventilator. Bronchospasm had not occurred in any case 
during this study. 
The median time for confirmation of tube position by capnography was 42 seconds. 
The maximum and minimum times were 67 seconds and 27 seconds respectively.  
As discussed earlier, this time was dependent on the intubation time which was person 
dependent. To standardize the outcomes and time taken, literature was searched for 
rate of ventilations suggested during capnography measurement. No guideline or 
recommendation could be found. Most literature and textbooks have mentioned rates 
of 10 - 12 manual bag ventilations per minute during capnography.  
The endotracheal tube in this study was connected after intubation to a preset 
ventilator with respiratory rate set at 26 ventilations per minute for standardization. 
This was excerpted from the study done by Pfeiffer et al31 who had used the same 
respiratory rate in their study for standardization. Using a fixed mechanical ventilation 
rate helped to study time for confirmation more precisely and reliably, as the 
performance of manual bag ventilations would be individual dependent. Individuals 
might perform manual bag ventilations faster or slower than the usual rates of bag 
ventilations. Individuals might deliver larger tidal volumes during manual bag 
ventilations which could be harmful. Using a fixed mechanical ventilation tidal 
volume also helped to avoid use of higher tidal volumes in this study.  
A ventilation rate of 26 ventilations per minute helped to minimize bias in time taken 
for confirmation of endotracheal tube by capnography compared to ultrasonography. 
Using slower ventilation rates could have favoured the results towards 
ultrasonography being faster than capnography. In event of oesophageal intubation, a 
high ventilation rate could have led to more abdominal distension in the subjects. 

64 
 
However, during this study, subjects with initial oesophageal intubation did not have 
abdominal distension or high airway pressures when observed in the ventilator such 
that nasogastric tube decompression of the stomach would be required. This study had 
excluded patients at risk of aspiration of gastric contents, and also patients with 
known cardiopulmonary diseases in whom abdominal distension leading to difficulty 
in ventilation resulting in hypoxemia and hemodynamic compromise could have 
occurred.  
This study used both sidestream and mainstream capnographs. This was because of 
availability of different types of capnograph at the study sites. The details of sampling 
line delay are discussed later. 
Ultrasonography vs Capnography 
Both ultrasonography and waveform capnography were found to be good, reliable and 
fairly accurate diagnostic methods of confirming endotracheal tube position. Though 
ultrasonography and capnography were equally sensitive and capnography seemed 
more specific; the sensitivity, specificity, PPV, NPV of ultrasonography were 
comparable (statistically not different as seen by their confidence intervals) to 
waveform capnography. 
The combination of ultrasongraphy and capnography increased precision (accuracy) 
over using either one of them in this study. Since the studies done previously had 
compared ultrasonography against capnography as the standard and thus calculated 
the sensitivity, specificity, PPV, NPV of ultrasound; these were not able to show if 
ultrasound had increased accuracy over using capnography alone.  

65 
 
Both of these methods are now known to be equally reliable. Hence in case of 
unmatched result given by these two methods in a patient, a third highly reliable 
method of confirmation has to be used because both ultrasonography and 
capnography have statistically not different false positive (1 – specificity) and false 
negative (1 – sensitivity) rates. 
There was generally good agreement between the results produced by 
ultrasonography and capnography as shown by the kappa value of 0.749 with 95% 
confidence interval of (0.567 – 0.931). Other studies have shown a good or a very 
good agreement of these two methods by kappa statistics. The kappa value calculated 
by Adi et al30, Chou et al28, Karacebay et al27 and Chintamani et al34 were 0.85, 0.93 
(0.84 – 1.00), 0.85 and 0.76 respectively. 
Real-time, transtracheal, transverse suprasternal ultrasonography was significantly 
faster (p = 0.011) than capnography by 16.36 ± 3.23 seconds (mean ± SD) in 
confirming endotracheal tube position in this study. The subgroup analysis between 
mainstream and sidestream capnographs also showed that the type of waveform 
capnograph device used did not affect the significant difference in time of ultrasound 
over capnograph in confirming endotracheal tube position.  
The sidestream capnograph at MCVTC had system response time of < 4 seconds, and 
that at TUTH had system response time of < 3 seconds. Adjusting for rise time of 200 
milliseconds (the actual rise time of sidestream capnograph device used at TUTH; the 
rise time of that used at MCVTC was unknown), the transit time (delay time) would 
be in between 3 to 4 seconds in MCVTC sidestream capnograph and in between 2 to 3 
seconds in TUTH sidestream capnograph. No delay was expected in mainstream 
capnograph device. 

66 
 
The median time taken for endotracheal tube confirmation by mainsteam capnograph 
was 37 seconds and that by sidestream capnograph was 45.5 seconds. The combined 
median time taken for endotracheal tube confirmation by capnography was 42 
seconds. The difference in time with ultrasonography was maximum of 19 seconds 
and minimum of 9 seconds while using mainstream capnograph, and maximum of 24 
seconds and minimum of 12 seconds while using sidestream capnograph. These 
findings correlate to the delay time of sidestream capnographs as mentioned 
previously. Though theoretically the delay time should not have exceeded 4 seconds, 
the difference in median time for confirmation between these types of capnographs 
was 8.5 seconds. The median time for confirmation of endotracheal tube position in 
this study would be affected by the time taken by the anaesthesia resident for 
intubation. Thus difference in time for confirmation between the two types of 
capnographs could be greater or lesser than 8.5 seconds depending on the variability 
of time taken for intubation in this study. 
Few studies have compared if ultrasound can be faster than capnography. Karacebay 
et al27 found that dynamic transtracheal ultrasound at suprasternal level combined 
with lung sliding done by two separate operators simultaneously during intubation, 
was faster in average by 5.9 seconds than capnography for endotracheal tube 
confirmation. Pfeiffer et al31 found that lung ultrasound was in average 7.1 seconds 
faster than capnography in confirming endotracheal tube position.  
The difference in time was greater in this study, likely due to use of sidestream 
capnograph. But as discussed earlier, this did not affect the significance in difference 
in time. 

67 
 
Chintamani et al34 in their study comparing ultrasound and capnography found mean 
± SD time for confirmation by ultrasound to be 12 ± 1.31 secs, and that by 
capnography to be 8.98 ± 1.04 secs. Their finding of capnography being significantly 
faster is debatable because they used transtracheal ultrasound at suprasternal level 
first in transverse view then in longitudinal view, followed also by scanning towards 
the left side of neck to align the area of oesophagus towards the center of probe. They 
also have not mentioned the criterion for capnography, whether ETCO2 values were 
used or not, and the number of waves they counted for a result. 
 
 
 
 
 
 
 
 
 
 

68 
 
LIMITATIONS 
 
1. This study used both sidestream and mainstream capnographs as per availability at 
the study sites. Sidestream capnographs have a delay time in reading exhaled CO2, 
which does not occur in mainstream capnographs.  
2. Different persons (anaesthesia faculties with training in airway ultrasound) 
performed ultrasound imaging in this study. 
3. This study did not see if novice ultrasound operators could also confirm 
endotracheal tube position by ultrasound imaging earlier than capnography. 
 
 
 
 
 
 
 
 

69 
 
CONCLUSION 
Ultrasonography and waveform capnography are equally reliable and accurate 
methods of confirming endotracheal tube position. Confirmation of endotracheal tube 
position by real-time ultrasonography is faster than capnography independent of the 
ultrasound operator. The combination of ultrasonography with capnography in 
practice will help reduce time and increase precision of confirming endotracheal tube 
position. 
 
 
 
 
 
 
 
 
 

70 
 
RECOMMENDATIONS 
• Real-time transtracheal ultrasonography is safe and can be used as an alternate 
method of confirming endotracheal tube position in operating theatres. 
• Using real-time transtracheal ultrasound can help confirm endotracheal tube 
position earlier than capnography. 
• Using real-time transtracheal ultrasound will help avoid manual bag 
ventilations to confirm endotracheal tube position and can prevent aspiration 
of gastric contents into lungs in cases of oesophageal intubation. 
 
 
 
 
 
 
 
 
 
 

71 
 
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2-D Ultrasound for Identification of Esophageal Intubation. The Journal of 
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45. Weaver B, Lyon M, Blaivas M. Confirmation of endotracheal tube placement 
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77 
 
APPENDIX A 
Pre-anaesthetic evaluation (PAC) form, Department of Anaesthesiology 
 
Front page: 
 
 
 
 
 

78 
 
Back page: 
 
 
 
 
 
 
 

79 
 
APPENDIX B 
CONSENT 
Department of Anaesthesiology, 
Tribhuvan University, Institute of Medicine, Kathmandu, Nepal. 
Study Title:   “Ultrasonography imaging versus waveform capnography in detecting  
endotracheal tube placement during intubation in a tertiary hospital.” 
Study Number/ Subject’s Initials: _______________  
Subject’s Name:_______________  
Date of Birth / Age: _________________                         
 
Please do initial in box (Subject)  
(i)  
I confirm that I have read and understood the information sheet and consent 
form dated __________ for the   above study and have had the opportunity to 
ask questions.  
 
(ii)  
I understand that my participation in the study is voluntary and that I am free 
to withdraw at any time, without giving any reason, without my medical care 
or legal rights being affected.  
(iii)  
I understand that the researchers and the IRB and other regulatory authorities 
will not need my permission to look at my health records both in respect of the 
current study and any further research that may be conducted in relation to it, 
even if I withdraw from the trial. I agree to this access. However, I understand 
that my identity will not be revealed in any information released to third 
parties or published.  
 
 
I agree not to restrict the use of any data or results that arise from this study 
provided such a use is only for scientific purpose(s)  
 
(v)  
I understand that there is no financial incentive for the investigator or the 
institute and hospital. I also understand that in event of any adverse outcome in 
the process of my stay in the hospital, there will not be any compensation in 
any form due to my involvement in this study. 
I agree to take part in the above study.  
 
 
Signature (or Thumb impression) of the Subject             Right                
Left 
 
_____________                                          
 Date: _____/_____/______  
Signatory’s Name: _____/_____/______  
Signature of the Investigator: ____________________________ Date: _____/_____/______ 
Study 
Investigator’s 
Name: 
__________________________________________________ 
Signature 
of 
the 
Witness 
______________________ 
Date:_____/_____/_______                    
Name of the Witness: ___________________________________ 

80 
 
APPENDIX C 
Proforma 
 
“Ultrasonography imaging versus waveform capnography in detecting 
endotracheal tube placement during intubation in a tertiary hospital”. 
Conducted by : Dr. Shirish Shakti Maskay, MD Resident in Anaesthesiology, IOM. 
Mobile no.: 9841564879. 
Preceptor: Prof. Dr. Bishwas Pradhan 
Co-guides: Dr. Priska Bastola, Dr. Ninadini Shrestha 
 
Participant serial no. :  
 
 
 
 
Date: 
Inpatient no.:  
 
 
 
 
 
Centre: 
Name/Ethnicity: 
 
 
 
 
 
Age/sex: 
Address: 
 
 
 
 
 
 
Phone: 
Weight / BMI : 
 
 
 
 
 
Ward: 
Diagnosis: 
Planned surgery: 
ASA status: 
 
 
 
Co-morbid conditions: 
Ongoing treatment/drugs: 
Airway assessment:  
Mouth opening/upper lip bite test / mallampati grade/ teeth/ neck circumference 
 
Temporo-mandibular joint/ neck / thyromental distance/ thyromental height 
 
Date of surgery : 
Hours of fasting: 

81 
 
Premedication : 
IV cannulation:  
 
 
 
IV fluid: 
Induction of general anaesthesia: 
Muscle relaxant: 
Endotracheal tube type and size: 
 
CL grade: 
 
ECG rhythm 
Pulse rate 
Blood Pressure 
SPO2 
Preop at OT recovery 
 
 
 
 
Prior to induction 
 
 
 
 
After induction of 
general anesthesia 
 
 
 
 
After intubation 
 
 
 
 
 
Endotracheal tube position showed by Ultrasound:     Trachea / Oesophagus: 
Time taken for tube position result by ultrasound: 
 
Endotracheal tube position showed by Capnography:       trachea (6 positive waves) / 
oesophagus (absence of positive waves or irregular waves after 6 ventilations) 
Time taken for capnography result: 
 
Reconfirmation of tube position:        Trachea / Oesophagus                                                                   
Auscultation                                                                                                                     
Lung sliding sign 
 
End results for both methods:                                                                           
Ultrasound: True positive / False positive / true negative / false negative            
Capnography : True positive / False positive / true negative / false negative    
 

82 
 
APPENDIX D 
Thesis approval letter from IRB