Prehospital measurement and treatment of ionised hypocalcaemia by UK helicopter emergency medical services in trauma patients: a survey of current practice.

BACKGROUND

In the United Kingdom (UK), an increasing number of Helicopter Emergency Medical Services (HEMS) carry blood products for the resuscitation of patients with suspected haemorrhage. Ionised hypocalcaemia can occur due to calcium chelation from citrate-containing blood products or in response to traumatic injury. Therefore, many HEMS administer calcium alongside prehospital blood product transfusion. There are no national guidelines for prehospital calcium replacement. This study aimed to explore current UK HEMS protocols for calcium replacement associated with prehospital blood product transfusion and to report point-of-care testing (POCT) availability. The survey also sought to identify clinicians' opinions on the measurement, significance, and management of trauma-induced ionised hypocalcaemia in the prehospital setting.

METHODS

A cross-sectional survey with single-staged purposive sampling was conducted between 26th September and 15th November 2024. The survey explored standard operating procedures (SOPs) for calcium replacement, the incidence of POCT, and clinicians' opinions on the measurement and treatment of ionised hypocalcaemia. The survey was sent to the medical director, research lead, or a nominated clinician at the 21 HEMS in the UK on the 26th September 2024. These services were also invited to participate via a post on X (formerly Twitter) and a presentation delivered at the National HEMS Research and Audit Forum (NHRAF) on 26th September 2024.

RESULTS

21 HEMS responded to the survey (100% response rate), and all carried prehospital blood products and calcium replacement therapy. Eleven different combinations of blood products were carried. 20/21 (95%) had a SOP for calcium replacement during prehospital blood product transfusion. POCT of ionised calcium (iCa2+) was available at 6/21 (29%) of services. None had an SOP outlining the use of POCT for trauma patients, nor did any SOP specify the timing for measuring iCa2+. Clinicians' opinions on the definition, measurement, and treatment of ionised hypocalcaemia varied widely.

CONCLUSION

Blood products and calcium replacement therapy are now carried by all UK HEMS, but POCT is not in widespread use. Significant variation exists in the combination of products carried, protocols for calcium replacement, and opinions on the management of trauma-induced hypocalcaemia during prehospital transfusion, which suggests a need for further evidence.