Randomized. Controlled Trial of the Utilization of High Flow Nasal Cannula for Oxygenation of Sedated Morbidly Obese Patients in the Endoscopy Suite
Phase: NA
Conditions: Morbid Obesity, Noninvasive Ventilation, Deep Sedation
Sponsor: Montefiore Medical Center

 
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TITLE: Use of High Flow Nasal Cannula during Sedation of Morbidly Obese 
Patients in the Endoscopy Suite 
Authors:  
Jay Berger MD/ PhD 
Elizabeth Vue MD 
 
BACKGROUND 
 
Obesity defined as a body mass index (BMI) of > 30 kg/m2 has been 
identified as an independent predictor of sedation-related complications in patients 
undergoing sedation for gastro endoscopic procedures 1,2,3.  A recent survey 
estimated that in 2011-2012 34.9% of adults in the United States were obese (BMI 
> 30kg/m2) and 6.4% were extremely obese (BMI >40%kg/m2)1.  Several 
physiologic changes occur, as a patient’s BMI increases from the normal range to 
the extremely obese range.  Respiratory physiology in morbidly obese patients is 
altered; specifically, the additional weight of the chest causes a decrease in chest 
wall motion and lung compliance.  The decrease in compliance increases the work 
of breathing andcauses the development of ventilation to perfusion mismatching 4. 
 
In addition to physiologic changes, increasing obesity also causes 
anatomical changes that affect the respiratory system.  The high incidence of 
obstructive sleep apnea in obese patients can interfere with gas exchange during 
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endoscopic procedures requiring chemical sedation by causing airway obstruction5.  
The effect positional changes have on oxygen saturation is amplified in obese 
patients6.  The physiologic and anatomic changes associated with obesity not only 
necessitate an increased vigilance when monitoring these patientsreceiving deep 
sedation, but also commonly require airway manipulation to ensure proper 
oxygenation and ventilation.   
The delivery of anesthesia used for obese patients for gastrointestinal 
procedures does not significantly differ from what is used in healthy patients. 
Patients often receive deep sedation, a state in which patients are not easily 
arousable, but are responsive to noxious stimuli. Typically sedation during 
endoscopic procedures is maintained with an intravenous anesthetic such as 
Propofol; however, the choice of anesthetic used is operator dependent and should 
be personalized to the patient’s medical history7. Regardless of thelevel of 
sedation, patients undergoing endoscopic procedures are typically provided with 
supplementary oxygenation via nasal cannula or face mask when a higher 
concentration of oxygen is required8,9. As a means to maintain ventilation in cases 
complicated by airway obstruction, physical maneuvers such as a chin lift or  jaw 
thrust may be performed, adjuncts such as oral and nasal airways may be placed, 
and lastly active positive pressure ventilation may be delivered via bag valve mask 
(BVM), laryngeal mask airway (LMA), or endotracheal tube (ETT)8.   The use of 
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high flow nasal cannula (HFNC) to deliver oxygen to morbidly obese patients is 
expected to decrease the need for the aforementioned interventions by producing a 
low level of positive end expiratory pressure (PEEP) that will prevent airways 
from collapsing. 
HFNC is a device that delivers gas through an air/oxygen blender generating 
flows up to 60 L/min, which is significantly greater than 1-6 L/min flow used with 
standard nasal cannulas5. The enhanced flow delivered via HFNC has several 
physiological consequences, which can potentially benefit obese patients. One 
benefit of HFNC is that it can provide PEEP, which is uncommon in open system 
methods of oxygen delivery5. Studies have shown a significant increase in positive 
pharyngeal pressure and subsequent increases in end expiratory lung volume with 
the use of HFNC, especially in patients with increased BMI6. The added PEEP 
helps prevent alveolar collapse, enhancing ventilation and oxygen delivery. By 
increasing the amount oxygen reserve in patients’ lungs, the frequency and length 
of oxygen desaturation caused by the sedation should be decreased; thereby 
decreasing the requirement of more invasive airway interventions.  Another benefit 
of HFNC is that the high flow rate is able to prevent a build up of CO2 by washing 
CO2 out of the airway dead space5. Outcomes that support improvement in 
oxygenation and ventilation from use of HFNC include a decrease in respiratory 
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rate and decrease in accessory muscle use during respiration, andincreases in the 
PaO2 andthe PaO2/Fi02 ratio10.  
The actual FiO2 that low flow systems such as nasal cannulas deliver is 
usually lower than predicted.  As flow rates increase, the actual FiO2 
deliveredmore closely approaches the predicted value. Using high flow oxygen 
will, therefore, give an anesthesiologist a better estimate of the concentration of 
oxygen that is delivered to the patient5.The air delivered via HFNC is both 
humidified and heatedto body temperature, thereby decreasing airway irritation 
and the incidence of bronchoconstriction, which is more common when cold dry 
air is used7.  
 
The numerous benefits of HFNChasmade it a valuable tool to assist in 
ventilation and oxygenation for patients in the intensive care setting.In theory, 
HFNC, addresses many of the respiratory complications that occur as a 
consequence of morbid obesity during sedation for medical procedures. We 
hypothesize that the use of HFNC during gastro endoscopic procedures requiring 
sedation in extremely obese (BMI >40 kg/m2) patients will improve ventilation 
and oxygenation and decrease the need for airway manipulation and increasing 
FiO2 levels during the procedure.   
OUTCOMES 
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The primary endpoint is to assess the effects of HFNC on maintaining ventilation 
and oxygenation. This will be ascertained through the need for airway 
manipulations such as chin lift and jaw thrust to the placement of airway adjuncts 
such as oral or nasal airways.   
In addition, the need for an increased FiO2 will be recorded. Secondary endpoints 
will include the lowest and mean pulse oximetry readings, TcCO2, TcO2, and the 
change in these values from the beginning to the end of the procedure.  Additional 
end points will record interruption or aborting of the procedure secondary to 
difficulties managing the patient’s airway.  Both groups will be placed on 
supplemental oxygen via nasal cannula and transported to the recovery room for 
observation prior to discharge.   Pulse oximetry readings will be followed for an 
hour every 15 minutes after the completion of the procedure in the recovery room 
to assess for desaturation. Participants will also be evaluated on how they feel prior 
to discharge. 
MATERIALS AND METHODS: 
STUDY POPULATION 
Participants are eligible for the study if they are greater than 18 years of age 
and are scheduled for an elective ambulatory upper and/or lower endoscopy under 
sedation in the gastrointestinal suite at the Moses Campus of the Montefiore 
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Medical Center.  Participants must have a BMI greater than or equal to 40 kg/m2. 
Inclusion in the study will be voluntary without monetary compensation. 
Participants will be excluded if they are less than 18 years of age,pregnant, have 
severe respiratory failure (hypercapneic and/or hypoxemic), use home oxygen at 
baseline, have a tracheostomy, or the procedure is an emergency.  Patient selection 
will be obtained by reviewing the GI suite schedule a few days ahead of time 
screening for patient with a BMI greater than 40.   
The patient’s chart will then be reviewed during the normal anesthesia pre-
operative assessment for criteria that would exclude the patient from the study.  If 
no exclusion criteria are found, the patient will be contacted by phone and the 
study will be explained and the patient verbally consented.  On the day of the 
procedure or if possible prior to the procedure the patient will sign written consent.  
The patients will be consented by a member of the study team. 
STUDY DESIGN 
Eligible patients will be randomized into two groups of thirtypatients each11, 
12.  The experimental group will receive oxygen via HFNC at 50 lpm and FiO2 of 
0.35 for the procedure.  The control group will receive oxygen via nasal cannula at 
5lpm(approximately an FiO2 of 0.35) for the procedure.Each participant will 
receive monitored anesthesia care (MAC) with moderate sedation with Propofol.  
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A loading dose of 1 mcg/kg ideal body weight followed by an infusion starting at 
125 mcg/kg/min and titrated to desired level of sedation.  At the discretion of the 
Anesthesiologist the patient may receive 50 to 100mcg of Fentanyl IV PRN.  All 
patients will be monitored using standard American Society of Anesthesiologists 
monitors, which include continuous EKG, heart rate, pulse oximetry, and non-
invasive blood pressure monitoring.  Monitoring end tidal carbon dioxide (ETCO2) 
to insure adequate ventilation by capnographyduring moderate sedation can be 
problematic, due to movement of the cannula or patient preference for mouth 
breathing preventing adequate uptake of expired gas for analysis.  In addition, the 
high flow rates of the HFNCprevent the measurement of ETCO2.  Ventilation will 
be monitored in both groups by observing chest movement and by ECG derived 
respiratory signals13.  In addition, transcutaneous CO2 (TcCO2)and O2 (TcO2) 
levels will be monitored throughout the procedure. 
Airway maneuvers required to aid in ventilation or oxygenation during the 
sedation portion of the procedure will be recorded and are classified as chin lift 
maneuver, airway insertion, increased FiO2, active ventilation, and lastly aborting 
of procedure or intubation.  Chin lift maneuver is characterized by lifting of the 
chin or jaw-thrust maneuver in order to improve ventilation and/or oxygenation.  
Insertion of an oral or nasal airway helps insure patency of the airway by 
preventing obstruction by the tongue.  Increased FiO2 will be achieved by 
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placement of face-mask over the patient’s mouth and nose, airway patency can be 
helped by applying a low level of positive pressure.  If oxygenation and/or 
ventilation continues to be problematic active ventilation can will be performed.  
The last classification is for any procedure that is aborted early due to respiratory 
complications or if the patient requires general anesthesia and intubation in order 
to insure proper ventilation/ oxygenation. 
This is a pilot study, so a small number of patients per group was initially 
chosen.  The number of patients in each group is based on our clinical observation 
while caring for patients in the endoscopy suite.  The analysis of the outcome data, 
the proportion of patients requiring additional airway support, will be analyzed 
utilizing chi-square analysis.  Current clinical practice at our hospital varies, the 
use of HFNC is a physician preference.  Even though it is considered as a standard 
of care, not all Anesthesiologists are experienced using it.  If the Anesthesiologist 
assigned to the case is not familiar with or not comfortable  with HFNC, the patient 
will be excluded from the study.  Although MAC sedation utilizing a nasal cannula 
for oxygenation is routinely performed, a significant number of morbidly obese 
patients are electively intubated and placed under general anesthesia for these 
endoscopic procedures.  Patients that are endotracheal intubated will be excluded 
from the study.  The research portion of the study is randomly assigning the 
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patients into one of two groups, every thing else follows the standard of care at our 
hospital. 
RANDOMIZATION 
This is a randomized controlled study. Anesthesia research office that is not 
part of the patient’s routine clinical care will generate the randomization list. 
Envelope containing computer generated randomized allocations will be given to 
the research team. Randomization envelopes will only be open 30 minutes prior to 
the procedure. To maintain the proper concealed allocation the research team will 
maintain a randomization sheet with randomization number, subject initials, time 
and date of the procedure.  
As all data is to remain anonymous and to be reported in aggregate (any 
value less than 1% will be aggregated with the most similar group (including 
diagnosis and age), we anticipate minimal physical, psychological risks to 
individual patients. 
Data will remain de-identified and no personal identifiers will be queried 
unless an outlier is found. Subsequent to review by the research team any outliers 
that cannot be excluded will receive a chart review. For chart review the IRB code 
will be kept in the desk of and used exclusively by the principle investigator. 
Following identification by the principal investigator,charts of outliers may be 
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reviewed for verification of number of opiate prescriptions. This data will be 
reconfirmed in the anonimized database/spreadsheet. 
 
STATISTICAL ANALYSIS 
Sample size calculation 
Primary objective of this study is to evaluate theeffects of HFNC on maintaining 
ventilation and oxygenation in the two groups. For the purpose of this study if a 
patient is getting 5or more air way manipulations such as chin lift and jaw thrust or 
any other direct interventions to maintain the ventilation and oxygenation will be 
categorized into the group need for additional support to maintain ventilation and 
oxygenation. According to our clinical audit when using the standard of care nasal 
cannula 90% of the patients required additional support for maintaining ventilation 
and oxygenation. HFNC is now been routinely used in our ORs. We have observed 
that in majority of the patients when HFNC was used the need for additional 
airway manipulations were minimal when compared to the regular oxygen cannula. 
For the purpose of this pilot study sample size calculations are based on the 
assumptions that 90% of patients using regular cannula will require additional 
airway manipulations while only 55% in the HFNC group requires the same. Based 
on a two-sided alpha of 0.05 and Type II error of 20% to achieve a statistically 
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significant difference between the two groups we need to study 25 patients in each 
group, a total of 50 patients. Additionally, we plan to increase our sample size by 
10% to accommodate for attritions. 
Analysis plan 
All the analysis will be intention-to-treat analysis. Standard descriptive statistics 
will be used to explain demographic and clinical characteristics (age, gender, type 
of surgery, pre-entry medications, ASA status, surgeon, co- morbidities, etc.). The 
analysis plan assumes that the primary outcome of the trial the proportion of 
patients requiring addition airway support will be analyzed using the chi-square 
analysis. Percentage of patients requiring FiO2 will also be analyzed using chi-
square analysis. For all continuous monitoring measurements such as TcCO2 and 
TcO2 the measurements will be averaged for first 5 minutes before the start of any 
procedure activities and this measurement will serve as the baseline measurement.  
For all subsequent measurements every 15 minute measurements will be averaged 
and a delta value will be created comparing it to the baseline.   The delta value 
created will be compared between the two groups. 
CONCLUSION: 
In the past decade, the obesity epidemic has resulted in a growing need for 
novel approaches to improve patient safety when receiving anesthesia. First shown 
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in the pediatric critical care literature and more recently in the adult critical care 
literature, HFNChas been shown to be useful in treating both hypoxic and 
hypercapnic respiratory failure.  This pilot study will investigate the utility of 
HFNC in insuring ensuring adequate ventilation and oxygenation of extremely 
obese patients during endoscopy procedures requiring sedation.  Our hypothesis is 
that HFNC will allow for improved and safer ventilation of extremely obese 
patients undergoing sedation, improving the quality of care for this specific patient 
population.  
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