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Cardiovascular complications of prehospital emergency anaesthesia in patients with return of spontaneous circulation following medical cardiac arrest: a retrospective comparison of ketamine-based and midazolam-based induction protocols
  1. Christopher King1,
  2. Asher Lewinsohn1,
  3. Chris Keeliher1,
  4. Sarah McLachlan2,3,
  5. James Sherrin4,
  6. Hafsah Khan-Cheema4,
  7. Peter Sherren1
  1. 1Essex & Herts Air Ambulance Trust, Essex, UK
  2. 2Research Department, Essex & Herts Air Ambulance, Essex, UK
  3. 3Department of Allied Health and Medicine, Anglia Ruskin University, Chelmsford, UK
  4. 4University College London Medical School, London, UK
  1. Correspondence to Dr Christopher King, Essex & Herts Air Ambulance Trust, Essex, Colchester CO6 2NS, UK; christopher.king2{at}


Background Hypotension following intubation and return of spontaneous circulation (ROSC) after cardiac arrest is associated with poorer patient outcomes. In patients with a sustained ROSC requiring emergency anaesthesia, there is limited evidence to guide anaesthetic practice. At the Essex & Herts Air Ambulance Trust, a UK-based helicopter emergency medical service, we assessed the relative haemodynamic stability of two different induction agents for post-cardiac arrest medical patients requiring prehospital emergency anaesthesia (PHEA).

Methods We performed a retrospective database review over a 5-year period between December 2014 and December 2019 comparing ketamine-based and midazolam-based anaesthesia in this patient cohort. Our primary outcome was clinically significant hypotension within 30 min of PHEA, defined as a new systolic BP less than 90 mm Hg, or a 10% drop if less than 90 mm Hg before induction.

Results One hundred ninety-eight patients met inclusion criteria. Forty-eight patients received a ketamine-based induction, median dose (IQR) 1.00 (1.00–1.55) mg/kg, and a 150 midazolam-based regime, median dose 0.03 (0.02–0.04) mg/kg. Hypotension occurred in 54.2% of the ketamine group and 50.7% of the midazolam group (p=0.673). Mean maximal HRs within 30 min of PHEA were 119 beats/min and 122 beats/min, respectively (p=0.523). A shock index greater than 1.0 beats/min/mm Hg and age greater than 70 years were both associated with post-PHEA hypotension with ORs 1.96 (CI 1.02 to 3.71) and 1.99 (CI 1.01 to 3.90), respectively. Adverse event rates did not significantly differ between groups.

Conclusion PHEA following a medical cardiac arrest is associated with potentially significant cardiovascular derangements when measured up to 30 min after induction of anaesthesia. There was no demonstrable difference in post-induction hypotension between ketamine-based and midazolam-based PHEA. Choice of induction agent alone is insufficient to mitigate haemodynamic disturbance, and alternative strategies should be used to address this.

  • anaesthesia - rsi
  • cardiac arrest
  • prehospital care
  • clinical management
  • pre-hospital

Data availability statement

Data are available upon reasonable request. Data are available on reasonable request from the corresponding author or from our patient liaison managers.

Statistics from

Data availability statement

Data are available upon reasonable request. Data are available on reasonable request from the corresponding author or from our patient liaison managers.

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  • Handling editor Caroline Leech

  • Contributors CKing—methodology, formal analysis, writing (original draft) and study submission. AL—methodology and writing (review and editing). CKeeliher—methodology and validation. SM—formal analysis and visualisation. JS—investigation. HK-C—investigation. PS—conceptualisation, formal analysis, writing (review and editing) and supervision.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were involved in the design, or conduct, or reporting, or dissemination plans of this research. Refer to the Methods section for further details.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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