Comparison of McGrath Videolaryngoscopy and Direct Laryngoscopy for Intubation in Patients With Morbid Obesity in Non-cardiac Surgery
Phase: NA
Conditions: Morbid Obesity
Sponsor: The Cleveland Clinic

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Comparison of McGrath Videolaryngoscopy and Direct Laryngoscopy for 
intubation in patients with Morbid Obesity  
(version 1, January 18th, 2018) 
(Version 2, August 16th, 2018) 
NCT03467048 
 
Kurt Ruetzler, MD1,2; Steve M. Leung, MD1; Sheerer, Christopher, DO3;  
Natalya Makarova, MS1,4;Sandeep Khanna, MD2; Karen Steckner, MD2; Turan 
Alpsaran, MD2;  Kamal Maheshwari, MD2;  Praveen Chahar, MD2;  Mi Wang, MD2;  
Daniel I. Sessler, MD1; and colleagues 
 
 
1. Department of OUTCOMES RESEARCH, Anesthesiology Institute, Cleveland Clinic, 
Cleveland, USA  
 
2. Department of General Anesthesiology, Anesthesiology Institute, Cleveland 
Clinic, Cleveland, USA 
 
3. Resident of Anesthesiology, Anesthesiology Institute, Cleveland Clinic, 
Cleveland, USA 
 
4. Department of Quantitative Health Sciences, Cleveland Clinic, Cleveland, USA 
 
 

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Summary of changes (version 2) 
 Exact timing of randomization was defined: After confirming adequate bag mask manual 
ventilation, patients will be randomized 1:1 and stratified for BMI >50 kg/m2 (Materials 
and Methods, page 7) 
 In cases of intubation failure, further airway management will be determined by the 
attending anesthesiologists. No airway device or technique will be proposed and rescue 
airway device/ technique will be documented (Materials and Methods, page 7) 
 Once the patient is intubated, the endotracheal cuff pressure will be measured once. 
(Materials and Methods, page 7) 
 Patients will be assessed for postoperative complications 2 hours after extubation, or at 
PACU discharge, whatever happens earlier (not follow up at wards) (Materials and 
Methods, page 8) 
 Some measurements during Airway examination (Materials and Methods, page 8), have 
been changed: 
o Mobility of cervical spine (0, 15, 30, and 45 degrees) 
o Mandibular protrusion test (Class A, B, C) 
o Teeth status: Edentulous, frontal teeth missing, or full dentures  
 
 

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Background 
Advanced airway management is often required for patients who need general anesthesia. Several 
supraglottic airway devices have been introduced into clinical practice during the last few decades, 
and are currently used on a regular base. However, endotracheal intubation (ETT) provides the 
best airway for mechanical ventilation and best prevents aspiration.  
Airway complications are rare but may lead to severe complications, such as brain damage and 
even death1. Set aside the “cannot ventilate and cannot intubation” scenario, difficult intubation 
has been associated with significant patient morbidity. For example, repeated intubation attempts 
are associated with respiratory and hemodynamic complications, including hypoxemia, cardiac 
arrest, regurgitation, aspiration, and airway trauma — along with bradycardia and cardiac arrest 
in emergency settings2 3.  
Obese patients present an airway challenge due to their unique anatomy, and are prone to early 
desaturation. Obese patients may also have comorbidities (e.g., diabetes) and increased intra-
abdominal pressure, which places them at higher risk of aspiration. Obese patients are thus 
generally intubated quickly to reduce the risk of aspiration. There is data suggesting that obesity 
is a significant predictor of difficult laryngoscopy4 and intubation5. As the incidence of obesity 
continues to rise, it will become increasingly relevant for clinicians to decide on the best airway 
management devices for these patients.  
Direct laryngoscopy (DL) has been the traditional method to insert an ETT.  DL generally requires 
a direct “line of sight” to visualize the glottis and insert an ETT. While obesity per se is not a difficult 
airway, obesity carries risk factors that can lead to difficult mask ventilation and/or difficult 
intubation due to a combination of:  
1. extra pre-tracheal soft tissue4,  
2. thoracic fat pads and large breasts interference with the standard DL handle6,  
3. limited neck mobility from laryngeal and cervical glycosylation from diabetes7.  
Videolaryngoscopes were introduced approximately two decades ago and have gained wide 
acceptance because they improve glottis visualization which may improve first-pass intubation 
success rate and decrease complications. There is continued debate whether videolaryngoscopy 

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is superior to DL on parameters including first time intubation success rates, complications from 
intubation, and clinical benefits. Several trials demonstrated that videolaryngoscopes improved 
vocal cord visualization, but not first-pass intubation success8,9. Interestingly in a trial with ICU 
patients, videolaryngoscopy did not improve first-attempt intubation success and was associated 
with severe complications including death, cardiac arrest, cardiovascular collapse and hypoxemia9. 
In contrast, other trials show improved glottis visualization, improved first-pass success,10 and no 
difference in rate of complications compared with DL11.  In a recent Cochrane review of more than 
seven thousand patients with and without difficult airways, videolaryngoscopy was associated 
with fewer complications (e.g., laryngeal or airway trauma, postoperative hoarseness, hypoxia), 
fewer failed intubations, and no increase in the time required for intubation12.  
Available literature is heterogeneous in study design, patient characteristics, and intubation 
provider experience. The extent to which videolaryngoscopes might facilitate intubation in obese 
patients thus remains unclear. Existing literature focused on obesity in the BMI range from 35-
40 kg/m2.13,14 There is a paucity of data comparing DL and videolaryngoscopes extremely obese 
patients, specifically those having a BMI ≥ 40 kg/m2.  
The McGrath (Medtronic, Minneapolis, MN) is an FDA-approved and commercial available 
videolaryngoscope that includes a Macintosh blade and a camera which provides an indirect view 
of the glottis. The McGrath has been tested in a variety of settings15-17 and consistently provides 
better glottis visualization than DL in patients with difficult airways18,19. However, intubation in 
morbidly obese patients (BMI ≥ 40 kg/m2) can be challenging and whether results from previous 
trials apply to these patients remains unknown.  
 
 

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Objectives and Hypotheses 
Our goal is to compare conventional direct laryngoscopy using a Macintosh blade with the 
McGrath videolaryngoscope for endotracheal intubation in morbidly obese patients. Specifically, 
we propose to test the primary hypotheses that videolaryngoscopy improves visualization of the 
vocal cords, defined as with modified Cormack and Lehane classification (primary outcome) versus 
direct laryngoscopy.   
We will also test the secondary hypotheses that McGrath videolaryngoscopy:  
1) Does not increase number of intubation attempts 
2) Does not increase the number of intubation failures. 
We will also assess the following exploratory outcomes: 
1. Ease intubation; 
2. Glottis opening score (POGO) score; 
3. Duration of intubation. 
We will also assess the following safety outcomes: 
1.  Incidence of cut lips, airway injury, or dental injury; 
2. Incidence of postoperative coughing;  
3. Incidence or severity of postoperative sore throat; 
4. Incidence or severity of postoperative hoarseness. 
 
 
 

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Materials and Methods 
Study Design 
We propose a patient-blind randomized trial that will be conducted at the Cleveland Clinic, Main 
Campus. 
Methods 
We will enroll up to 136 adult patients, with American Society of Anesthesiologists (ASA) physical 
status of 1-3, who are scheduled for elective non-cardiac surgery requiring endotracheal 
intubation for general anesthesia. Informed consent will be obtained in the pre-anesthesia 
evaluation clinic. Intubators will be experienced anesthesia providers with sufficient experience, 
defined by having performed at least 75 with direct laryngoscopy and 75 with the McGrath system.  
Inclusion criteria 
 Elective surgery requiring oral endotracheal intubation for general anesthesia; 
 Anticipated extubation in the operating room; 
 American Society of Anesthesiologists (ASA) physical status 1-3; 
 Age between 18 and 99 years; 
 Body Mass index ≥ 40 kg/m2. 
Exclusion criteria 
 Refusal of participation by attending anesthesiologist;  
 Indicated rapid sequence induction for any reason including, but not limited to high risk of 
aspiration 
 Indicated fiberoptic awake intubation. 
 
Protocol 
In the preoperative period, patient’s airway data will be recorded by a research coordinator or 
anesthesia provider (Table 1). Patients will be positioned supine and in a standardized ramped 

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position on the OR table. Patients will be pre-medicated with midazolam 0-2 mg IV, as clinically 
appropriate. All patients will be pre-oxygenated until the fraction of expired oxygen exceeds 80%. 
General anesthesia will be induced as preferred by the attending anesthesiologist, usually with a 
combination of lidocaine 1 mg/kg, propofol 2-5 mg/kg, fentanyl 1-3 µg/kg, and rocuronium 0.6-
1.2 mg/kg or succinylcholine 1.5 mg/kg.  
Manual bag-mask ventilation will be initiated, with no restriction on the use of oral airways, nasal 
airways, laryngeal masks. Complete muscle relaxation will be confirmed by absence of palpable 
twitches in response to supra-maximal train-of-four stimulation of the ulnar nerve at the wrist. 
After confirming adequate bag mask manual ventilation, patients will be randomized 1:1, stratified 
for BMI >50 kg/m2, to: 
 Direct laryngoscopy using an appropriately sized Macintosh blade (usually size 3 or 4); 
 McGrath videolaryngoscopy in an appropriate size (usually blade size 3 or 4). 
Randomization will be based on computer-generated codes accessed from the Redcap system.  
Intubations will be performed with a regular endotracheal tube of adequate diameter, usually 7.5 
mm or 8.0 mm. Endotracheal tubes will be equipped with a hockey-stick-shaped stylette, which 
will be prepared by the anesthesiologist in advance.  
The McGrath or the Macintosh blade will be introduced into oral cavity according to manufacturer 
recommendations and clinical practice. Minor airway manipulation procedures including BURP or 
Sellick maneuvers will be allowed to improve visualization of the vocal cords.  
If initial intubation attempts fails, the endotracheal tube will be removed and manual bag mask 
ventilation will resume.  Minor adjustments of patient’s position and/or tube stylette are allowed 
as clinically appropriate. Up to three intubation attempts will be made as necessary. 
Further airway management will be determined by the attending anesthesiologists and not further 
airway device/ technique is proposed by this study protocol. Any further airway technique and 
device will be documented. 
Once intubation is achieved, the endotracheal tube will be connected to the anesthesia circuit, 
and the endotracheal cuff pressure will be measured placed between 25 and 30 cm H2O. 

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Mechanical ventilation with O2 and air will be adjusted to maintain end-tidal PCO2 between 32 and 
35 mmHg as clinically necessary. The endotracheal tube cuff will be measured once. Maintenance 
of general anesthesia will be provided, as clinically indicated.  
At the end of the surgical procedure, patients will be extubated and transferred to the post 
anesthesia care unit (PACU). Patients will then be assessed for postoperative complications 2 
hours following extubation, or at PACU discharge.  
 
Measurements 
Table 1. Demographic and morphometric characteristics will be collected from electronic 
medical records.  
1. Age 
2. Gender 
3. Race 
4. BMI  
5. ASA status 
6. Airway examination 
a. History of obstructive sleep apnea (yes/no) 
b. History of snoring (yes/no) 
c. History of CPAP (yes/no) 
d. History of difficult airway (yes/no) 
e. Mobility of cervical spine (0, 15, 30, and 45 degrees) 
f. Mouth opening (cm)  
g. Inter-incisor gap (cm)  
h. Mandibular protrusion test (Class A, B, C) 
i. Thyro-mental distance (cm)  
j. Sterno-mental distance (cm)  
k. Neck circumference (cm)  
l. Upper lip bite test (Class I, II, III) 

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m. Mallampati score (1/2/3/4) 
n. Teeth status: Edentulous, frontal teeth missing or full dentition.  
 
Primary outcome: 
 Best glottis visualization, defined as visualization according to the modified Cormack and 
Lehane classification20 
 
 
Secondary Outcomes: 
 Intubation attempts, defined as introducing the endotracheal tube into oral cavity to 
perform endotracheal intubation (1, 2, 3, more than 3) 
 Intubation failure, defined as  
o Grade IV visualization 
o failure to intubate within 3 intubation attempts 
o need to switch intubators or intubation device  
o need to stop study per anesthesiologist’s discretion  
Exploratory outcomes: 
 Portion of glottis opening score (POGO) score, defined as estimation of the glottis, which 
is visible during laryngoscopy (0, 25, 50, 75, 100%)21,22 

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 Time to intubation, defined as the time between the endotracheal tube introduced into 
oral cavity and first appearance of end-tidal CO2. 
 Ease of intubation, defined as subjective evaluation of the anesthesiologist after finishing 
the intubation procedure (1) very easy, (2) easy, (3) moderate, (4) difficult, (5) 
impossible23,24 
Safety outcomes: 
 Any obvious airway and teeth injury including bleeding, airway trauma, dental fracture, 
aspiration, or bronchospasm. 
 Incidence and severity of postoperative cough, assessed 2 hours after extubation or at 
discharge from PACU (whatever happens earlier), and defined as continuous throat pain 
and rated as mild (less than a common cold), moderate (similar to a common cold), or 
severe (more than a common cold).23,24 
 Incidence and severity of postoperative sore throat, assessed 2 hours after extubation or 
at discharge from PACU (whatever happens earlier), defined as an acoustic quality that was 
different from the previous voice quality of the patients and rated as mild (less than a 
common cold), moderate (similar to a common cold), or severe (more than a common 
cold).23,24 
 Incidence and severity of postoperative hoarseness, assessed 2 hours after extubation or 
at discharge from PACU (whatever happens earlier), and rated as noticed by the patient 
only, apparent to an observer, or aphonia.23,24 
Statistical Analysis 
We will assess the balance of two randomized groups (McGrath videolaryngoscopy vs. direct 
laryngoscopy) on baseline and demographic characteristics using the absolute standardized 
difference (ASD), defined as the absolute difference in means, mean ranks, or proportions divided 
by the pooled standard deviation. Any characteristics with ASD > 0.2 will be considered imbalanced 
and will be adjusted for in the primary and secondary analyses.  

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All primary and secondary analyses will be completed using the intent-to-treat principle, thus 
including all randomized patients in the analyses. We will conservatively assign all missing 
evaluations as the highest possible score in the control group (direct laryngoscopy) and the lowest 
possible score in the treatment group (McGrath videolaryngoscopy) for all primary and secondary 
analyses. 
 
Primary outcomes: 
Mann–Whitney U test will be used to formally compare categorical outcome of glottis visualization 
(Cormack and Lehane classification) at 5% significance level between the two study groups; the 
suggested test accounts for the ordinal nature of the outcome. A proportion of patients by glottis 
visualization classes will be reported for each randomized group.  
 
Secondary outcomes: 
The following secondary categorical variables will be compared between two study groups via 
Chi-square tests and corresponding odds ratio [97.5% confidence interval (CI)]: 
1. incidence  of intubation failures;  
2. the proportion of patients requiring 1, 2, 3, and more than 3 intubation attempts 
We will test if a McGrath videolaringoscopy is noninferior (i.e., not worse) than direct 
laryngoscopy on the listed below outcomes. We a-priori defined the noninferiority deltas for the 
outcomes: 
1. incidence  of intubation failures (noninferiority delta: 10% increase in intubation failures or 
1.10  using odds ratio); 
2. intubation attempts  (noninferiority delta: 1.10  using odds ratio);  
Noninferiority of McGrath videolaringoscopy versus direct laryngoscopy will be claimed for an 
outcome at the 0.025 significance level if the upper limit of 97.5% CI is below the corresponding 
noninferiority delta. 

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A Bonferroni correction for multiple testing will be applied and a significance criterion of 
0.05/2=0.025 will be used for secondary hypotheses testing correspondently to control the overall 
Type I error at 5% level for secondary hypotheses.  
The exploratory and safety outcomes will be reported by study groups without formal statistical 
testing of the difference. 
 
Sample size consideration 
Sample size consideration is based on primary outcome glottis visualization grade. We assume 
that about 75% of the patients would have Grade 1 visualization by Cormack and Lehane 
classification with direct laryngoscopy. Thus, 65 patients per group (N=130 total) would provide 
about 90% to identify a 20% increase in proportion of Grade 1 visualization (up to 95% of the 
patients) in the McGrath videolaryngoscopy group at the 5% alpha significance level. Other 
scenarios with different assumptions are presented in the Table below. (The situation described 
above is scenario #5). 
 
Computed N per Group 
Scenario 
# 
Alpha 
Ref 
Proportion 
Proportion 
Diff 
Actual 
Power 
N per 
Group 
1 
0.05 
0.70 
0.15 
0.90 
161 
2 
0.05 
0.70 
0.20 
0.90 
82 
3 
0.05 
0.73 
0.15 
0.90 
145 
4 
0.05 
0.73 
0.20 
0.90 
73 
5 
0.05 
0.75 
0.20 
0.90 
65 
 
 
Pilot patients 
We will enroll 4-6 pilot patients prior to the start of the study to familiarize the study team with 
the protocol and identify any systematic issues that might result in protocol modifications. Pilot 
patients will be randomized either to McGrath videolaryngoscopy or direct laryngoscopy group in 

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the same manner as it is planned for the study. Therefore, we are planning to enroll a total of 136 
patients to the study. 
 
Funding: 
This study will be supported by a grant by Medtronic.  
 
 
 

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