High-flow nasal cannula (HFNC) oxygen therapy has increased in popularity in recent years due to its superiority over conventional oxygen therapy in reducing treatment failure, particularly among small children.1 The utilization of HFNC has also been expanded from critical care units to general care wards, emergency departments, and procedure rooms.2 There are several known physiologic benefits of HFNC oxygen therapy: meeting and/or exceeding patient inspiratory flow, providing a constant fraction of inspired oxygen (FIO2) and a small amount of positive airway pressure, and washing out the anatomic dead space.1-3 Additionally, the warmed and humidified gas allows for patient comfort and tolerance. Thus, it is reasonable to employ HFNC oxygen therapy during endoscopic procedures to assure adequate oxygenation. Compared to conventional nasal cannula oxygen therapy, HFNC has been reported to reduce the episodes of hypoxemia during endoscopy.2 While it is promising that HFNC oxygen therapy may be useful during procedures like endoscopy, the results of available studies need to be interpreted cautiously. It is not yet known if HFNC oxygen therapy is the most cost-effective way to assure adequate oxygenation during endoscopic procedures. Additionally, while HFNC oxygen therapy may be useful for some patients, it may not be necessary for all.
So far, six randomized controlled trials have been published on the use of HFNC oxygen therapy during endoscopy,4-9 all of which included adult patients. Three were during bronchoscopy,4-6 while the other three were during esophagogastroduodenoscopy or colonoscopy.7-9 Among the latter three studies, all of which included patients with healthy lungs and normal oxygenation prior to examination, fewer incidences of hypoxemia during examination were reported. In two of the studies, HFNC oxygen therapy with gas flows at 30-60 L/min and FIO2 set at 1.0, HFNC oxygen therapy was compared to a standard nasal cannula set at 2-5 L/min.7,8 There was no difference in the incidence of hypoxemia in the Riccio et al study where HFNC oxygen therapy with gas flows of 60 L/min and FIO2 at 0.36-0.4 was compared to nasal cannula at 4 L/min.9 The difference of set FIO2 during HFNC oxygen therapy among the three studies probably explains the conflicting results,2 instead of the set flow rate.
The benefits of high gas flows typically associated with HFNC oxygen therapy may be reduced during an endoscopic examination simply due to the procedure itself. Those procedures require the mouth to be open for bite-block and scope access to the site of interest. With the mouth open, the positive pressure generated by HFNC decreases by up to 50%.10 Additionally, the actual inhaled FIO2 may be lower than the set FIO2 due to air entrainment from mouth breathing.10 This also decreases some of the humidification provided by the device. Hypoxemia caused by obstructed/collapse airways during procedural sedation11 is still likely if HFNC oxygen therapy is used, since it might not be useful to treat or prevent airway obstruction.
The reduction in the known benefits of HFNC oxygen therapy during an endoscopic procedure probably explain the results of the randomized controlled trial completed by Klotz and colleagues12published in this edition of Pediatric Pulmonology . Their study was the first study to report on the use of HFNC during endoscopy examinations for pediatric patients. In their study, they enrolled and treated 25 patients with HFNC and 25 patients with low-flow nasal cannula that received sedation for an upper gastrointestinal tract endoscopy. The groups were similar except more patients in the HFNC group had a higher prevalence of snoring (32% vs 8%) and rate of first-hand smoke exposure (24% vs 0%).12 Similar oxygen flow rates (mL/min/kg) were used in both groups, although there were different gas flow rates used (L/min). This suggests that FIO2, not the gas flow rate, plays the most important role in preventing hypoxemia during endoscopy examination with the mouth open.
In a prior study, other investigators have demonstrated that HFNC oxygen therapy was superior to nasal cannula for gastroscopy.7 However, it should be noted that in this particular study, HFNC oxygen therapy at 60 L/min with FIO2 at 1.0 was compared to nasal cannula at 2 L/min and the study required a sample size of nearly 2,000 to show superiority of HFNC over conventional nasal cannula.7 This raises a cost-effectiveness question regarding the use of HFNC during endoscopic examination, since those procedures often last for less than one hour. The FIO2 provided by conventional nasal cannula is indeed limited and increasing FIO2 by raising oxygen gas flow is not ideal, due to discomfort from the relatively cool and dry gas. Other conventional oxygen devices may be able to provide a high FIO2 at a lower cost, such as non-rebreather mask. These masks, by providing a higher FIO2, might reduce hypoxemia during endoscopy similarly to HFNC oxygen therapy. That said, future studies are needed to confirm if this is indeed true. Regardless of the type of oxygen devices used during endoscopic procedures and procedural sedation, close monitoring of patient respiratory status and early identification and treatment of respiratory failure is crucial.11-13
HFNC might be an effective option for high-risk patients during endoscopy, such as patients who have hypoxemia prior to endoscopy.4,5 It may also be useful during high-risk procedures, such as during bronchoscopic examination as the bronchoscope may increase airway resistance and work of breathing. Longer-lasting bronchoscopic procedures such as endobronchial ultrasound6 or biopsies14 or bronchoaveolar lavage may negatively impact oxygenation require HFNC oxygen therapy instead of a conventional low-flow oxygen therapy via nasal cannula. HFNC oxygen therapy has been shown to be similar to noninvasive ventilation in avoiding hypoxemia during bronchoscopic examination.4,5 Compared to the use of noninvasive ventilation during endoscopy, HFNC oxygen therapy is less cumbersome and less expensive. Perhaps most importantly, it may be better tolerated by the patient.
It appears that HFNC should not be used in all patients undergoing an endoscopic procedure. Transient hypoxemia can be managed by increasing oxygen flow via conventional low-flow nasal cannula. HFNC oxygen therapy may be considered in high-risk patients, such as those that have hypoxemia prior to endoscopy. It could also be considered during high-risk procedures that last for long periods of time or those that may negatively affect oxygenation, such as biopsy or bronchoalveolar lavage via bronchoscopy. Regardless of the oxygen delivery modality, close monitoring of respiratory status and intervention when needed is crucial for patient safety.
AUTHORS’ CONTRIBUTIONS
J.L. drafted the manuscript; J.B.S and J.H.L. provided critical revision on the manuscript.
CONFLICT OF INTEREST
Dr. Li declares to receive research funding from Fisher & Paykel Healthcare Ltd and Rice Foundation. Mr. Scott discloses a relationship with Ventec Life Systems and Teleflex. Dr. Lee has no conflict of interest to declare.