Disclaimer: This article is intended solely for informational and educational purposes only. It does not constitute medical advice.
Moderate sedation is commonly used across multiple specialties, including gastroenterology, emergency medicine, ophthalmology, and more. It induces a state of lowered consciousness and relaxation in which the patient remains able to respond purposefully and maintain airway patency. Because respiratory depression is the principal safety concern during sedation, supplemental oxygen is typically administered. However, it is unclear if supplemental oxygen prevents or masks this complication, which has produced research on its use in the context of moderate sedation, with results varying by delivery method, patient risk profile, and monitoring strategy employed.
Low-flow supplemental oxygen via standard nasal cannula, the most common approach in moderate sedation, has shown limited benefit in reducing hypoxia. In a randomized, double-blind trial of emergency department patients sedated with midazolam and fentanyl, Deitch et al. found no difference in the incidence of hypoxia between patients receiving 2 L/min supplemental oxygen and those receiving compressed air (Deitch et al., 2007). Notably, capnography identified respiratory depression in a substantial proportion of patients whose oxygen saturation never dropped below 90%, and physicians failed to recognize any of these events using standard monitoring alone.
Consequently, this creates a risk that oxygen supplementation can delay desaturation without addressing underlying hypoventilation, potentially enabling a patient’s condition to worsen rapidly and unexpectedly (Deitch et al., 2007). Lightdale et al. reached a complementary conclusion in pediatric endoscopy, where capnography-guided intervention that prompted nurses to stimulate patients based on early signs of alveolar hypoventilation significantly reduced arterial oxygen desaturation even though all patients received routine 2 L supplemental oxygen, suggesting that ventilatory monitoring rather than oxygen alone is what drives safety outcomes (Lightdale et al., 2006).
A systematic review and meta-analysis of 19 randomized trials found that high-flow nasal oxygen (HFNO) reduced hypoxemia by 63% compared with conventional oxygen delivery, increased minimum oxygen saturation, and reduced the need for airway maneuvers and procedural interruptions, with the benefit consistent across gastrointestinal, bronchoscopy, and endovascular procedures and across risk strata (Thiruvenkatarajan et al., 2023). Notably, HFNO had no measurable effect on hypercarbia, indicating that its benefit stems from oxygenation and dead-space washout rather than improved ventilation (Thiruvenkatarajan et al., 2023).
The multicenter ODEPHI trial reinforced this finding in a population specifically selected for hypoxemia risk, showing that supplemental high-flow nasal oxygen at a matched inspired oxygen fraction reduced desaturation events, prolonged desaturation, and the need for airway maneuvers compared with standard oxygen therapy delivered at an equivalent FiO2 in patients undergoing endoscopy with moderate sedation (Nay et al., 2021). These results isolate the physiologic effect of flow and positive airway pressure from the effect of oxygen concentration alone.
However, not all high-flow approaches are equivalent. In patients undergoing endoscopic retrograde cholangiopancreatography, nasal high-flow delivered with room air (no supplemental oxygen) did not reduce hypercapnia or hypoxemia compared with low-flow oxygen, suggesting that the ventilatory benefits of high flow without added oxygen may be insufficient in this setting (Sawase et al., 2023).
Clinicians should not assume supplemental oxygen alone protects against respiratory depression during moderate sedation and should be aware that its use may in fact obscure early warning signs. High-flow nasal oxygen delivered with adequate FiO2 appears to meaningfully reduce hypoxemic events, particularly in patients at elevated risk, but should be paired with ventilatory monitoring rather than substituted for it.
References
Deitch, K., Chudnofsky, C. R., & Dominici, P. (2007). The utility of supplemental oxygen during emergency department procedural sedation and analgesia with midazolam and fentanyl: A randomized, controlled trial. Annals of Emergency Medicine, 49(1), 1–8. https://doi.org/10.1016/j.annemergmed.2006.06.013
Lightdale, J. R., Goldmann, D. A., Feldman, H. A., Newburg, A. R., DiNardo, J. A., & Fox, V. L. (2006). Microstream capnography improves patient monitoring during moderate sedation: A randomized, controlled trial. Pediatrics, 117(6), e1170–e1178. https://doi.org/10.1542/peds.2005-1709
Nay, M.-A., Fromont, L., Eugene, A., Marcueyz, J.-L., Mfam, W.-S., Baert, O., Remerand, F., Ravry, C., Auvet, A., & Boulain, T. (2021). High-flow nasal oxygenation or standard oxygenation for gastrointestinal endoscopy with sedation in patients at risk of hypoxaemia: A multicentre randomised controlled trial (ODEPHI trial). British Journal of Anaesthesia, 127(1), 133–142. https://doi.org/10.1016/j.bja.2021.03.020
Sawase, H., Ozawa, E., Yano, H., Ichinomiya, T., Yano, R., Miyaaki, H., Komatsu, N., Ayuse, T., Kurata, S., Sato, S., Pinkham, M. I., Tatkov, S., Ashizawa, K., Nagata, K., & Nakao, K. (2023). Respiratory support with nasal high flow without supplemental oxygen in patients undergoing endoscopic retrograde cholangiopancreatography under moderate sedation: A prospective, randomized, single-center clinical trial. BMC Anesthesiology, 23, 156. https://doi.org/10.1186/s12871-023-02125-w
Thiruvenkatarajan, V., Sekhar, V., Wong, D. T., Currie, J., Van Wijk, R., & Ludbrook, G. L. (2023). Effect of high-flow nasal oxygen on hypoxaemia during procedural sedation: A systematic review and meta-analysis. Anaesthesia, 78(1), 81–92. https://doi.org/10.1111/anae.15845