Scientific Papers

Induction of pre-hospital emergency anaesthesia i-PHEA: a national survey of UK HEMS practice | BMC Emergency Medicine


It is believed that this is the first survey to date that has sought to establish PHEA provision and what, if any, are the common induction regimes used in UK HEMS practice. Most services can be considered high volume PHEA providers [7], with 79% (n = 15/19) delivering over 100 anaesthetics in the previous 12-months. This gives the potential for a large data set by which the induction regimes and response to induction of anaesthesia can be monitored in detail and consider the effects on patient physiology and outcome. Future work should focus on the development of a national HEMS PHEA registry that would further inform clinical practice.

Two studies conducted by the Pre-hospital Trainee Operated Research Network (PHOTON) sought to establish PHEA provision across UK HEMS in 2020, as part of wider studies into geo-temporal provision of PHEA and compliance against the NICE 45-minute quality standard [9, 10]. Of note, the geo-temporal analysis of PHEA only reported provision at two points in time; a Tuesday and a Sunday in the summer of 2018 [10]. Whilst this study goes some way to describing the provision of PHEA across a 24-hour period, it is difficult to generalize the findings across a 365-day period, where several factors may affect the provision and subsequent delivery of PHEA, including availability of staff, weather issues that may affect flight, and variances in regional populations. Data presented confirms that the UK HEMS systems deliver an increasing number of PHEAs per annum (n = 1755 PHEAs in 12-month period, 1 April 2017 to 31 March 2018 inclusive [9]), which are similar to the results found in this survey (15 providers delivering over 100 PHEA per annum). Neither study explicitly examined induction regimes utilized.

Except for post-ROSC patients, there is consensus amongst all responding organisations in the approach to what agents are used in the induction of anaesthesia, namely a combination of fentanyl, ketamine and rocuronium. Rocuronium appears to be the only paralytic agent that is used in UK HEMS practice, representing a change in practice since a 2017 survey by Burgess et al [7] where several other agents were available. A limitation of this study was the pre-loaded questions that focused solely on the use of rocuronium and did not consider any other paralytic agent. However, there were no additional paralytic agents highlighted in free-text responses, suggesting that rocuronium is the only agent in use. Analysis of free-text responses indicated a move towards increased dosing of rocuronium across all patient groups, ranging from 1.4 mg/kg to 2 mg/kg. This represents a further change in practice from the dose regimes described by Lyon et al [2] in 2015. The optimal dose of rocuronium remains unclear [11], but there is a trend toward improved first pass intubation success where higher doses (> 1.4 mg/kg) are administered as part of the induction (92.2% first pass success (dose > 1.4 mg/kg) versus 88.4% first pass success (dose < 1.0 mg/kg)) [11]. Organisations responsible for PHEA delivery should consider moving toward a higher dose strategy of rocuronium, and further work is warranted to inform this change.

There are several plausible explanations for favorable intubating conditions with higher dose rocuronium, particularly when used in combination with video laryngoscopy. The higher dose rocuronium may saturate the synapse more quickly, and the increased availability of the drug in a patient with poor cardiac output increases drug distribution [11]. Modern, plastic based video laryngoscopes are less stimulatory than the colder, metal direct laryngoscopes, and as such reduces the stimulatory effects when inserted into the airway. However, further work is required to better understand the association of dose and intubating conditions.

As of 2019, a consensus statement from the European HEMS and Air Ambulance Committee Medical Working Group specified no particular drugs or regimes for PHEA, in favour of a regime that included an induction agent, an opioid and a fast acting muscle relaxant [12]. UK practice has favoured fentanyl, ketamine and rocuronium as either a 3:2:1 or 1:1:1 regime since 2015 [2]. This represented a shift from the use of agents such as etomidate and suxamethonium [13], and the findings of this survey suggest that there has been a further change in how induction of anaesthesia is delivered, as evidenced by the limited consensus approach to drug regimes in hemodynamically stable patients (Table 1). There is a trend to moving away from the standardized 3:2:1 approach, to a modified approach that is becoming increasingly practitioner choice and dependent upon the patient’s physiology, injuries, age, and comorbid state (Table 2). Although fentanyl remains commonplace in pre-hospital anaesthetic practice, there widespread variability in its use, and the dose used, varying from 1mcg/kg to 3mcg/kg in stable patients. This service evaluation did not seek to establish any cause or effect of the use of fentanyl, and further in-depth exploration of the effects on patient’s physiology is warranted. However, when considering hemodynamically compromised patients, there is a clear signal that most organisations utilize an induction regime of ketamine and rocuronium only (53%, n = 10/19). The development of a national PHEA registry would add further evidence to the role of fentanyl in PHEA, and organisations should continue to adopt a pragmatic, patient centered approach to anaesthesia.

The European Resuscitation Council post-resuscitation care guidelines do not recommend one agent over another for post-ROSC anaesthesia, in favour of a combination of a sedative, analgesic and rapid onset neuromuscular blocking agent [14]. Ketamine may cause an increase in heart rate and blood pressure, and increased myocardial oxygen demand, though it is unclear whether this adversely affects clinical outcome. Although increased heart rate and blood pressure may be favourable in the bradycardic, hypotensive post ROSC patient, increased myocardial oxygen demand may worsen ongoing ischemia. The use of fentanyl and midazolam therefore seem a reasonable alternative to ketamine in post-ROSC anaesthesia. Despite this, a quarter of organisations surveyed (26%, n = 5/19) adopt a regime that uses ketamine during post-ROSC anaesthesia, with 47% (n = 9/19) organisations using a variable, practitioner choice approach to anaesthesia. The emphasis, as in all pre-hospital anaesthetics, is to balance haemodynamic instability during induction with adequate anaesthesia. Acknowledging differences in patient physiology should be a key consideration when selecting drugs and doses.

There are important safety considerations when using a standardized approach to PHEA, including reduced cognitive loading in often stressful situations, and reduced drug errors [13]. The trend in moving away from didactic regimes highlight the maturity of UK HEMS practice and the increase in delivery of PHEA. Robust governance systems that monitor practice are commonplace in UK HEMS, and there is growing recognition that not all patients will fit within a prescribed regime.

Limitations

Duplication of survey response was minimised by specifically targeting organisational medical leads. This may introduce bias towards what is written in policy and procedure compared to actual clinical practice. Clinical practice and delivery of anaesthetic drugs may vary considerably between operators, and it is then difficult to quantify and measure each individual variance.



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