Association of Cerebral Oxygenation During Prehospital Anaesthesia and Functional Outcome: A Prospective, Observational Multi-Centre Cohort Study of 1014 Patients.

BACKGROUND: Many patients undergoing prehospital anaesthesia may be at risk of inadequate cerebral oxygenation due to underlying conditions or adverse events like hypotension or hypoxia. This study examined whether a decrease in regional cerebral oxygen saturation (rSO2) measured with near-infrared spectroscopy (NIRS) during prehospital anaesthesia associates with worse outcomes. METHODS: We conducted a prospective, observational study including adult patients anaesthetised by six prehospital critical care teams. A relative cerebral desaturation event (rCDE) was defined as a ≥ 10% decrease in rSO2 for ≥ 5 min from baseline. An absolute cerebral desaturation event (aCDE) was defined as rSO2 < 60% during anaesthesia or lower than baseline if already < 60%. The primary outcome was favourable functional outcome (modified Rankin Scale ≤ 2) at 30 days and secondary outcomes included 30-day survival, 1-year functional outcome, and 1-year survival. RESULTS: Among 1014 patients, 199 experienced an rCDE, with 125 (63%) having supraphysiological baseline. rCDE was not associated with outcomes. Of 182 patients with aCDE, 30-day favourable outcomes were not significantly different (30% vs. 36%, p = 0.14, adjusted OR 0.92, 95% confidence interval 0.62-1.34). However, aCDE was associated with lower 30-day survival (46% vs. 58%, p = 0.006) and less favourable 1-year outcomes (31% vs. 41%, p = 0.043). Adjusted analyses showed no significant associations. CONCLUSION: An rCDE was not associated with worse functional outcomes. While aCDEs were linked to unfavourable outcomes in unadjusted analyses, these associations were not significant after adjustment, highlighting the complexity of interpreting NIRS in heterogeneous populations. Condition-specific studies are needed to clarify its role. EDITORIAL COMMENT: Cerebral oxygen delivery may be jeopardized in critically ill patients undergoing prehospital anaesthesia. This study assessed near-infrared spectroscopy on the forehead in a large number of cases requiring general anaesthesia and subsequent transportation to hospital by helicopter. In unadjusted analysis, patients with an at least 10% decline in forehead saturation had higher survival and better functional outcome, whereas those with a forehead saturation below 60% had lower survival and worse functional outcome. Upon multivariable regression, age, patient category, systemic oxygen saturation and Glasgow Coma Scale score were independent predictors of worse outcomes, but forehead oxygen saturation was not. NIRS-measured forehead saturation decrease appears to associate in a complex fashion with more traditional predictors of patient outcomes. Whether effects of resuscitation interventions like these can be assessed reliably by NIRS is not yet well understood. TRIAL REGISTRATION: The study protocol was published beforehand on clinicaltrials.gov (NCT04144803) on 7th October 2019.