As the volume and complexity of outpatient surgical procedures continues to grow, it is essential for clinicians to be prepared for cases of unplanned conversion from regional anesthesia or sedation to general anesthesia (GA). While typically managed successfully and safely, conversion to general anesthesia is a significant event in anesthetic care that warrants an examination of associated patient outcomes.
Monitored anesthesia care (MAC) is used in approximately one-third of all ambulatory surgical procedures in the United States, and the American Society of Anesthesiologists (ASA) requires that any provider administering MAC be prepared to convert to general anesthesia and rescue the patient’s airway if needed¹. Despite this expectation, large-scale data on the incidence and consequences of conversion have been limited. A retrospective study by Kim et al. analyzing over 219,000 non-obstetric MAC cases at a large academic medical center found an overall conversion rate of 0.50%¹.
While this figure appears reassuringly low in isolation, it represents over 1,000 patients in a single institution over thirteen years, and the reasons for conversion carry distinct risk profiles. Approximately half of all conversions were patient-driven—most commonly due to failed regional or neuraxial anesthesia, followed by patient intolerance of MAC—while the other half were attributable to physiologic derangements including hypoxia, airway obstruction, hemodynamic instability, and aspiration¹.
Failed peripheral nerve block is one of the most common precursors to unplanned conversion to general anesthesia in the ambulatory orthopedic setting. Bottomley et al. note that block failure leading to conversion may arise from patient-related factors such as obesity and anatomical variability, provider-related factors including experience and equipment familiarity, or surgical factors such as unanticipated procedure extension². Critically, the authors emphasize that conversion to general anesthesia should be anticipated and discussed with the patient in advance as part of the informed consent process².
The consequences of conversion to general anesthesia may extend beyond the operating room—for example, neuraxial anesthesia failure requiring conversion is associated with higher complication risk and poorer patient outcomes, including respiratory complications, difficult or failed airway management, aspiration, and prolonged recovery. In a multicenter prospective study examining failed spinal anesthesia across general surgical populations, Demilie et al. found a failure rate of 22.4% in their cohort. 5% of those failures ultimately required conversion to GA; for comparison, the Royal College of Anaesthetists’ recommended benchmark is under 3%³.
Evidence from outside the ambulatory setting reinforces these concerns. Large-scale registry data demonstrate that patients who undergo regional anesthesia for orthopedic surgery tend to have fewer postoperative complications and shorter hospital stays than those receiving general anesthesia. These benefits are partially, though not entirely, attenuated when neuraxial anesthesia is combined with GA, suggesting that regional anesthesia alone improves outcomes and that conversion itself may introduce increased risk⁴. For example, it may produce additional hazards associated with emergent airway management under suboptimal conditions5.
Taken together, the literature supports a proactive rather than reactive approach to the risk of conversion to general anesthesia. Identifying patients at highest risk—those with obesity, high ASA physical status, complex anatomy, or procedures in high-conversion surgical subspecialties such as orthopedics and otolaryngology—allows for more deliberate preoperative planning¹. Ensuring that both providers and patients understand the possibility of conversion, and that teams are prepared to execute it smoothly when required, remains the most effective strategy for minimizing its impact on patient outcomes².
References
1. Kim, S., Chang, B. A., Rahman, A., Lin, H.-M., DeMaria, S., Zerillo, J. & Wax, D. B. Analysis of urgent/emergent conversions from monitored anesthesia care to general anesthesia with airway instrumentation. BMC Anesthesiol.21, 183 (2021). https://pmc.ncbi.nlm.nih.gov/articles/PMC8240303/
2. Bottomley, T., Gadsden, J. & West, S. The failed peripheral nerve block. BJA Educ. 23, 92–100 (2023). https://pmc.ncbi.nlm.nih.gov/articles/PMC9947978/
3. Demilie, A. E., Denu, Z. A., Bizuneh, Y. B. & Gebremedhn, E. G. Incidence and factors associated with failed spinal anaesthesia among patients undergoing surgery: a multi-center prospective observational study. BMC Anesthesiol. 24, 129 (2024). https://link.springer.com/article/10.1186/s12871-024-02484-y
4. Memtsoudis, S. G., Sun, X., Chiu, Y.-L., Stundner, O., Liu, S. S., Banerjee, S., Mazumdar, M. & Sharrock, N. E. Perioperative comparative effectiveness of anesthetic technique in orthopedic patients. Anesthesiology 118, 1046–1058 (2013). https://pmc.ncbi.nlm.nih.gov/articles/PMC3956038/
5. Simonsen, C. Z., Schönenberger, S., Hendén, P. L., Yoo, A. J., Uhlmann, L., Rentzos, A., Bösel, J., Valentin, J. & Rasumussen, M. Patients Requiring Conversion to General Anesthesia during Endovascular Therapy Have Worse Outcomes: A Post Hoc Analysis of Data from the SAGA Collaboration. American Journal of Neuroradiology 41(12), 2298-2302 (2002). https://pmc.ncbi.nlm.nih.gov/articles/pmid/33093133/