More dogmatic practice questioned - could 50% oxygen be the next 100%?
Matthew J Rowland MD, Ethan Sanford MD, Proshad Efune MD Shawn Jackson MD PhD
An often-debated topic is what FiO₂ to deliver to a healthy patient under anesthesia? Should it be left at 100%? Many of us would say NO due to development of toxic free radicals associated with high oxygen concentrations and the inflammatory response to surgery.1 Adult studies in anesthesia have shown increased risks of acute kidney injury, myocardial injury, and lung injury with supraphysiologic oxygen levels.2 Additionally, 100% oxygen causes absorption atelectasis by washing out alveolar nitrogen. Without nitrogen to stent the airways open, the remaining oxygen is rapidly absorbed into the bloodstream, leading to alveolar collapse and a reduction in functional residual capacity (FRC). Since pediatric patients have a high oxygen consumption per minute and often a reduced FRC in the supine position, their physiology would suggest they are at even higher risk of absorption atelectasis compared to adults.
Despite these concerns, many anesthesiologists still default to using around 50% FiO₂.4 Some feel there is little harm in delivering excessive FiO₂ for a short period to increase precious time if a critical event occurs (hypoventilation, mucus plug, kinked ETT, bronchospasm, unplanned extubation etc).
But what about during induction? Most still default to 100% oxygen delivery on induction for adequate pre-oxygenation, increased safe apneic time during laryngoscopy, and avoidance of any hypoxemic episodes in the event of difficult mask ventilation or laryngospasm. But does this practice increase atelectasis? Is that atelectasis in turn decreasing FRC enough to outweigh the benefits of being on 100% oxygen?
Dr. Tian and colleagues attempt to help shed light on this concept in today’s PAAD, where they look at the delivery of FiO₂ during induction and the development of anesthesia induced atelectasis in pediatric patients.
Original Article
Tian YQ, Wei W, Liu YQ, Xiao YY, Liu KJ, Li JH, Peng XM. Lung Ultrasound Evaluation of the Impact of Inspired Oxygen Fraction on Atelectasis During Induction of General Anesthesia in Pediatric Patients: A Randomized Controlled Trial. Shock. 2025 Dec 30. doi: 10.1097/SHK.0000000000002793. Epub ahead of print. PMID: 41697232.
In this clinical trial, 114 healthy (ASA I or II) pediatric patients aged 1-7 years old were randomized to receive 100% FiO₂ or 50% FiO₂ during anesthesia induction.5 In the 100% group, the FiO₂ was decreased to 50% at the end of 10 minutes and lung ultrasound was performed at 6 different time points by a blinded evaluator. The authors measured only clinically significant atelectasis defined as having at least one lung region with a lung ultrasound score of 2 or higher (atelectasis that was >5mm in size). Importantly, this degree of atelectasis is associated with increased post-operative pulmonary complications.6
The 100% FiO₂ group had much more atelectasis than the 50% group - 67% of cases receiving 100% compared to only 33% of cases in the 50% cohort (p < 0.001). Atelectasis was much more common in the gravity dependent lung regions, especially in the 100% FiO₂ group. Most importantly, there were no hypoxemic events in either group during or after induction; remarkably, all patients maintained an oxygen saturation of 98% or above.
Could delivery of 50% FiO₂ really be as safe as delivery of 100% FiO₂ during induction? The article inspires consideration of the risks of 50% FiO2 (time/hypoxemia) versus the risk of pulmonary complications. High PaO2 can still be achieved on 50% oxygen, providing adequate time for laryngoscopy without causing hypoxemia.7 The PAAD suggests the risk of induction with 50% FiO2 are low. However, we must interpret the results of this study with some caution. The authors only included healthy ASA I and II patients with normal BMIs scheduled for elective surgery with an oral endotracheal tube. They excluded large populations of patients, including those undergoing laparoscopic surgery (as laparoscopy independently causes atelectasis), those with recent upper respiratory tract infections, difficult airways, pre-existing atelectasis, or any history of cardiac or pulmonary disease/surgery.
Additionally, all patients underwent an intravenous induction, not an inhaled one, which perhaps explains some of the lack of hypoxemia. There were other notable differences compared to typical practice. These included using the ventilator to mask the patient, larger tidal volumes (8-10 as opposed to 6-mL/kg), and most importantly, no positive end expiratory pressure (PEEP) was used, a practice nearly condemned in modern PICU or OR practice. In short, this is a study of healthy children undergoing ideal circumstances for induction.
Within this context, should we elect for 50% FiO2 during IV induction of healthy kids? The risk seems low while providing some potential benefit. At minimum, this study reminds us that higher isn’t always better and that absorption atelectasis occurs frequently, particularly with 100% FiO₂.
What are your thoughts and practices regarding FiO₂ delivery during induction for pediatric patients? How have your practice patterns changed since training and over time? Send your thoughts to Myron (myasterster@gmail.com) and he will post in a Friday reader response!
References
1. Junod AF. Oxygen free radicals and lungs. Intensive Care Med. 1989;15 Suppl 1:S21-23. PMID: 2723243.
2. McIlroy DR, Shotwell MS, Lopez MG, Vaughn MT, Olsen JS, Hennessy C, Wanderer JP, Semler MS, Rice TW, Kheterpal S, Billings FT 4th; Multicenter Perioperative Outcomes Group. Oxygen administration during surgery and postoperative organ injury: observational cohort study. BMJ. 2022 Nov 30;379:e070941. PMID: 36450405
3. Balcarcel DR, Coates BM, Chong G, Sanchez-Pinto LN. Excessive Oxygen Supplementation in the First Day of Mechanical Ventilation Is Associated With Multiple Organ Dysfunction and Death in Critically Ill Children. Pediatr Crit Care Med. 2022 Feb 1;23(2):89-98. PMID: 35119429
4. Billings FT 4th, McIlroy DR, Shotwell MS, Lopez MG, Vaughn MT, Morse JL, Hennessey CJ, Wanderer JP, Semler MW, Rice TW, Wunsch H, Kheterpal S. Determinants and Practice Variability of Oxygen Administration during Surgery in the United States: A Retrospective Cohort Study. Anesthesiology. 2024 Sep 1;141(3):511-523. PMID: 38759157
5. Tian YQ, Wei W, Liu YQ, Xiao YY, Liu KJ, Li JH, Peng XM. Lung Ultrasound Evaluation of the Impact of Inspired Oxygen Fraction on Atelectasis During Induction of General Anesthesia in Pediatric Patients: A Randomized Controlled Trial. Shock. 2025 Dec 30. PMID: 41697232.
6. Wang Q, Li Y, Zhao K, Zhang J, Zhou J. Optimizing perioperative lung protection strategies for reducing postoperative respiratory complications in pediatric patients: a narrative review. Transl Pediatr. 2024 Nov 30;13(11):2043-2058. PMID: 39649647.
7. Zhang C, Xu F, Li W, Tong X, Xia R, Wang W, Du J, Shi X. Driving Pressure-Guided Individualized Positive End-Expiratory Pressure in Abdominal Surgery: A Randomized Controlled Trial. Anesth Analg. 2021 Nov 1;133(5):1197-1205. PMID: 34125080.
8. Balmaks E, Kentish SE, Seglenieks R, Lee JH, McGain F. Financial and environmental impacts of using oxygen rather than air as a ventilator drive gas. Anaesthesia. 2022 Dec;77(12):1451-1452. PMID: 36039020.