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.