Invasive arterial blood pressure monitoring to detect post-intubation hypotension in patients who receive a prehospital emergency anaesthetic for suspected traumatic brain injury

Background The prehospital management of moderate/severe traumatic brain injury (TBI) centres on the prevention of secondary brain injury. In some cases, prehospital emergency anaesthesia (PHEA) may be required to provide optimal neuroprotective care. Continuous invasive arterial blood pressure (IBP) monitoring is increasingly utilised in this cohort. PHEA can result in significant blood pressure changes, particularly around induction. IBP allows for a more targeted approach to blood pressure management in these patients. The aim of this study was to analyse hypotension frequency, depth and duration in suspected TBI patients monitored with IBP before PHEA. Methods A retrospective analysis of suspected TBI patients attended by Air Ambulance Charity Kent Surrey Sussex who received IBP prior to PHEA between the 6 January 2022 and the 6 July 2024. The magnitude and duration of ‘absolute hypotension’ (systolic blood pressure (SBP) < 90mmHg) were combined to establish a ‘dose’ of absolute hypotension (mmHg*min). The primary endpoints were the incidence and dose of absolute hypotension. Results 305 patients were identified, of which 140 (45.9%) were included. Median age was 58 years (interquartile range (IQR) 42–73), predominant sex was male ( n  = 108, 77%) and median Glasgow Coma Scale (GCS) was 6/15 (IQR 4.0–7.5). Thirteen patients (9.3%) were found to have an episode of absolute hypotension pre-PHEA, increasing to 53 (37.9%) post-PHEA. Twenty-five patients (47.2%) had an initial absolute hypotensive episode occur after five minutes post-PHEA, with a median duration of three minutes (IQR 1.0–4.5). The median dose of absolute hypotension was 144 mmHg*min (IQR 3.75–1675.5). Twenty-five patients (17.9%) had ‘clinically important hypotension’ (SBP < 110mmHg) pre-PHEA, increasing to 80 post-PHEA (57.1%). Pre-PHEA absolute and clinically important hypotension were found to be associated with both the incidence and dose of post-PHEA absolute hypotension. Conclusion This study highlights a higher incidence of absolute hypotension using IBP compared to previous studies utilising intermittent non-invasive blood pressure monitoring. While post-PHEA absolute hypotension was common, over half of these events were brief (less than five minutes). These findings highlight the importance of analysing depth and duration of hypotension and suggest the need for prehospital outcome-based studies utilising continuous IBP.