Emergency medical service
The East of England is a geographic area of 20,000 km2, containing a population of approximately 6.4 million people . The East of England Ambulance Service NHS Trust (EEAST) provides the statutory Emergency Medical Service (EMS) response in this region, and has been previously described . The EMS response can be augmented by one of five physician-CCP HEMS teams; dispatched at the discretion of the CCP-led critical care desk at one of the EEAST Emergency Operation Centres .
The core of each team consists of a physician and a CCP with at least three years’ post-registration experience. However, to facilitate education and training, a clinical supervisor frequently accompanies the core team. Supervisors are most often a senior physician, but when training a new CCP this role is undertaken by a senior CCP . Physicians in these teams are predominantly emergency medicine (EM) or anaesthesia consultants or senior registrars, with a minimum of six months training in hospital anaesthesia and extensive experience in the management of acutely unwell and injured patients. Prior to independent practice, physicians undergo further specialist training in pre hospital care, including a period of supervised practice and a local formative assessment by a pre hospital care consultant. Within ICOM systems, the decision as to who will perform laryngoscopy is typically decided before scene arrival, according to training needs, experience, team dynamics, and previous missions. Three of the five HEMS in the East of England utilise ICOM; two are operated by East Anglian Air Ambulance (EAAA) and one is operated by Magpas Air Ambulance (Magpas). Both services are classified as high-volume HEMS (> 50 PHEA cases per annum) , and have similar operating models that have been previously described [11, 14].
Both organisations deliver PHEA according to a shared standard operating procedure. This includes a standardised drug regime (ketamine 1–2 mg/kg, rocuronium 1 mg/kg, ± fentanyl) . Typically intubation was performed using direct laryngoscopy. From 2017, the option (for use at the discretion of the operating clinician) of videolaryngoscopy was introduced (McGrath® videolaryngoscope, Aircraft Medical, Edinburgh, UK). Standard practice does not include the routine application of cricoid pressure, and if required, neck immobilization is performed with manual inline stabilization with an open/absent cervical collar. Both services use the HEMSbase electronic medical record software (MedicOne Systems Ltd, UK).
In this retrospective observational study, a consecutive sample of trauma patients (as recorded in HEMSbase) ≥ 16 years old, attended to by EAAA (1st January 2015 to 31st December 2020) or Magpas (1st November 2015 to 31st December 2020, owing to later implementation of HEMSbase), and who underwent PHEA (defined as drug-assisted intubation) were included.
Each clinical record was reviewed by one of the study authors to identify exclusions, which included: unascertainable patient age, secondary transfer cases, duplicate cases, patients intubated in arrest, intubation by a non-HEMS team provider, and mechanisms not meeting the definition of trauma (injury through the transfer of kinetic energy); including medical cases initially coded as ‘trauma’, overdose, hanging, asphyxiation, burns, drowning, electrocution (and similar non-trauma mechanisms).
The first-pass intubation success rate of physicians compared to CCPs.
Secondary outcomes were: (1) report the cumulative first, second, third, and fourth-pass intubation success rates; (2) compare the pre-PHEA physiology and characteristics likely to affect intubation success in patients whose initial intubation attempt was undertaken by a physician compared to a CCP; (3) report the proportion of initial intubation attempts and FPS rate by professional group (CCP, EM physicians, anaesthesia physicians); (4) compare the crossover rate between professional groups. The crossover rate concerns the cohort of patients with a failed initial intubation attempt and was calculated as the proportion of cases in which the professional group of the final successful intubation was different to that of the initial unsuccessful attempt.
Data were extracted from HEMSbase at both organisations, and included: patient demographics (age, sex, estimated weight—as a surrogate for body mass index owing to the absence of patient height data), whether the patient was trapped on the arrival of HEMS (e.g. in a damaged vehicle), PHEA (HEMS team members and role, number of intubation attempts, provider professional group), and pre-PHEA physiological variables (heart rate (HR), respiratory rate (RR), systolic blood pressure (SBP), diastolic blood pressure (DBP), and shock index (SI); HR divided by SBP). Combined data were collated into a single data sheet in Excel (Microsoft Corporation (2021), Microsoft® Excel for Mac, Version 16.45), and stored on a secure EAAA server.
Physiological variables were captured from time-calibrated patient monitors (EAAA—X Series, ZOLL Medical Corporation, Runcorn, UK; Magpas—Tempus Pro, Philips Electronics UK Ltd, Farnborough, UK) as part of standard patient care, and uploaded automatically to HEMSbase. Physiological data from each case was reviewed by one of the study authors from the HEMSbase output, and overtly erroneous entries were deleted. If the data was equivocal, a decision to include/exclude was reached by consensus of three authors (JP, KL, EB) after independent review of all available case notes.
This study met the UK National Institute for Health Research criteria for a service evaluation. All data used for this study are routinely collected as part of standard prehospital data collection; formal ethical approval was therefore waived. The study was approved and registered with the EAAA Department of Research, Audit, Innovation & Development (EAAA 2021/001) and the Magpas Air Ambulance Clinical Governance Group. The study design complied with the STROBE (Strengthening the Reporting of Observational studies in Epidemiology) reporting guidelines .
Data have been reported as number (percentage), number (percentage (95% confidence interval (95% CI), Wilson/Brown method)), and mean (± standard deviation) or median [interquartile range] as appropriate. Fisher’s exact test has been used to compare two proportions, and is reported with a Baptista-Pike calculated odds ratio (OR) with 95% CI (Wilson/Brown method) and a p value; three-way analysis of proportions has been analysed with a Chi-square test and is reported as a p value. Normally distributed data have been compared with an unpaired, two-tailed Student’s t test (with Welch’s correction for unequal standard deviations) and reported as a p value. Non-normally distributed data have been compared with a Mann–Whitney U test and reported as a p value. Statistical analyses were performed in Prism for MacOS (v.9.2.0, GraphPad Software, San Diego, CA, USA), using the software’s recommended analyses; significance was pre-defined at < 0.05 and no corrections were made for multiple comparisons.