Maintenance of prehospital anaesthesia using an intermittent bolus regime in blunt trauma patients with a high GCS and hemodynamic reserve: a retrospective cohort study

BACKGROUND: In-hospital intravenous maintenance of anaesthesia is commonly achieved by continuous infusion, while prehospital maintenance of anaesthesia after rapid sequence induction (RSI) is currently commonly provided by intermittent boluses. However, the practice effect of this approach has never been fully established. METHODS: In a single centre retrospective observational study at a helicopter emergency medical service (HEMS) in the UK, post-RSI anaesthesia maintenance by intermittent boluses was studied between 1 January 2019 and 28 February 2023. Time- and weight-adjusted average maintenance drug doses (as a surrogate for efficacy of sedation) were calculated for a consecutive sample of 101 blunt trauma patients receiving a prehospital anaesthetic with a Glasgow Coma Scale (GCS) ≥ 9 and without significant cardiovascular instability. Associations between (cumulative) maintenance drug doses and induction doses, patient characteristics, physiological parameters, and anaesthesia duration were evaluated using Pearson correlation coefficients and 95% confidence intervals. RESULTS: Median time of prehospital anaesthetic duration was 56 min (range 16-116 min). Maintenance dosing of fentanyl clustered around a median [IQR] dose of 0.64 [0-1.41] mcg/kg/h (minimum non-zero: 0.26mcg/kg/h, maximum: 5.56 mcg/kg/h). For midazolam, this was 0.028 [0-0.041] mg/kg/h (minimum non-zero: 0.005 mg/kg/h, maximum 0.157 mg/kg/h), and for ketamine 0 [0-0.23] mg/kg/h (minimum non-zero 0.05 mg/kg/h, maximum: 1.62 mg/kg/h). Eight patients (duration of anaesthesia between 48 and 74 min), received no maintenance sedation or analgesic agents. No clinically relevant associations were identified between maintenance dosing of any agent and induction dosing, patient demographics or pre-induction physiological parameters. CONCLUSION: This retrospective analysis of a homogeneous cohort of patients with haemodynamic reserve and a GCS ≥ 9 undergoing prehospital emergency anaesthesia showed that anaesthesia maintenance by an intermittent bolus-only regimen comes with notable variability in cumulative doses administered and may result in a potential risk of sub-therapeutic plasma levels.