A 47-year-old man with a body mass index of 38 kg/m2 and known obstructive sleep apnea is scheduled for endoscopic retrograde cholangiopancreatography. The plan is to provide monitored anesthesia care sedation using a targeted propofol infusion and titrated fentanyl. According to a recent study, which outcome is MOST likely if he receives high-flow nasal oxygen therapy instead of low-flow nasal cannula plus mouthguard oxygen delivery?
(A) Similar likelihood of hypoxemia ✔
(B) Higher likelihood of hypercarbia X
(C) Lower patient satisfaction X
Read the discussion below.
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High-flow nasal oxygen (HFNO) can provide up to 70 L/min of 100% FIO2 and has been shown to decrease the rate of hypoxemia in patients undergoing certain procedures with sedation. However, there has been considerable heterogeneity in the patients and procedures evaluated in most studies examining the use of HFNO. Few studies have assessed the impact of HFNO on hypoxemia in patients receiving sedation for endoscopic retrograde cholangiopancreatography (ERCP).
A recent randomized controlled trial (the Oxygen Therapy in High-Risk ERCP [OTHER] trial) was conducted to compare the effects of supplemental oxygen administered via HFNO versus low-flow nasal cannula plus mouthguard oxygen delivery in patients at high risk for adverse respiratory events during elective ERCP. The trial was conducted from February 2019 through September 2020 at 3 separate hospitals in Australia. Patients more than 18 years of age were included if they met any of these criteria: American Society of Anesthesiologists (ASA) physical status of III or higher, body mass index greater than 30 kg/m2, or known or suspected obstructive sleep apnea. Patients were excluded if they had a known or suspected difficult airway, had severe cardiopulmonary disease, were at risk of aspiration, were undergoing emergency ERCP, or received general anesthesia with tracheal intubation.
Patients were randomly assigned to either the HFNO group or the low-flow nasal cannula plus mouthguard oxygen (“low-flow”) group. Blinding was not possible given the different physical characteristics of the oxygen delivery devices. The HFNO group received 100% FIO2 at flows ranging from 30 L/min to 60 L/min. The low-flow group received 4 L/min of oxygen via nasal cannula and an additional 4 L/min of oxygen through the mouthguard device (8 L/min total oxygen delivery). A transcutaneous carbon dioxide (TcCO2) monitor was used, in addition to the standard ASA monitors. The sedation regimen consisted of a target-controlled infusion (TCI) of propofol and titrated doses of fentanyl. Patients were placed in the prone or lateral position at the discretion of the gastroenterologists. Anesthesia providers followed a protocol for responding to subclinical hypoxemia and hypercarbia, using predefined airway interventions as needed.
The primary study outcome was the development of hypoxemia (SpO2 < 90%) for any duration. Secondary outcomes included the number of hypoxemia episodes; lowest SpO2; highest TcCO2; occurrence of hypercarbia; requirement for minor airway interventions (chin lift, jaw thrust, or nasopharyngeal airway placement); requirement for major airway interventions (bag-mask ventilation or tracheal intubation); patient satisfaction with the route of oxygen delivery; development of potential adverse effects of oxygen therapy (dry nose, mouth, or throat; abdominal bloating); and occurrence of cardiac arrhythmias. Duration of the procedure was factored into the analysis because of the expectation that patients who were sedated for longer procedures may have an increased risk of developing hypoxemia.
There were 65 patients in the HFNO group and 66 patients in the low-flow group. Baseline characteristics were similar between the 2 groups. Hypoxemic events occurred in 7.7% of patients in the HFNO group and 9.1% of patients in the low-flow group. On statistical analysis, these rates were not found to be different (percentage point difference, –1.4%; 95% CI, –10.9 to 8.0). Even after adjusting for duration of the ERCP procedure, the rate of hypoxemia remained similar between the 2 groups. None of the patients who experienced a hypoxemic event had more than 1 episode.
No differences were found between groups for the lowest SpO2 (97.1% in the HFNO group vs 95.5% in the low-flow group; 95% CI, –0.2 to 3.4); highest TcCO2 (7.4 kPa [55.5 mm Hg] in the HFNO group vs 7.8 kPa [58.5 mm Hg] in the low-flow group; 95% CI, –1.4 to 0.6); and rate of hypercarbia (41.8% in the HFNO group vs 33.9% in the low-flow group; 95% CI, –10.1 to 26.2). The lowest SpO2 was less than 80% in 3 patients in the low-flow group and 0 patients in the HFNO group. No differences in the use of minor or major airway interventions, adverse effects of oxygen therapy, and cardiac arrhythmias were found between groups. Patient satisfaction scores were similarly high in both groups. No serious adverse events occurred in either group.
The rate of hypoxemia in this study was lower than that of other studies in the literature, which was unexpected since the study population consisted of patients at increased risk of adverse respiratory events. The authors surmised that this lower rate may be attributed to 1 or more of the following: the addition of mouthguard oxygen delivery to nasal cannula oxygen delivery in the control group, the titrated TCI protocol for propofol, and the careful titration of opioids. The authors also noted that the amount of positive airway pressure that can be generated by HFNO is notably reduced when the mouth is open (as occurs during all upper endoscopy procedures).
In summary, this study found that the rate of hypoxemia was similar between HFNO and low-flow nasal cannula plus mouthguard oxygen delivery in patients at high risk of adverse respiratory events undergoing ERCP procedures with titrated TCI-based propofol sedation.
- Thiruvenkatarajan V, Dharmalingam A, Arenas G, et al. Effect of high-flow vs. low-flow nasal plus mouthguard oxygen therapy on hypoxaemia during sedation: a multicentre randomised controlled trial. Anaesthesia. 2022;77(1):46-53. doi:10.1111/anae.15527
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