Title: Triggers for prehospital transfusion of packed red blood cells: a systematic review of the literature

Background and Goal of Study: Early administration of blood products is increasingly advocated in the treatment of patients with life-threatening haemorrhage, and Emergency Medical Services are increasingly transfusing red blood cells (RBC) before arrival at a hospital. However, consensus about prehospital transfusion triggers is lacking. This systematic review aims to evaluate which criteria are currently used for prehospital transfusion.

Materials and Methods: PubMed and Web of Science were searched through June 2016 using a standardized search strategy. Manuscripts reporting criteria for prehospital transfusion of RBC (PTRBC) in patients with major bleeding (traumatic and non-traumatic) were eligible for inclusion. Abstracts were screened, and the full-text of all potentially eligible articles were retrieved. Reported transfusion criteria were classified as ‘major criteria’ or ‘minor criteria’, depending on whether only one criterion needed to be met to initiate PTRBC, or whether a combination of several criteria was required.

Results and Discussion: The search yielded 1616 articles. 6 articles that were mentioned in references were also included. Some articles discussed the criteria of the same groups. In that case, only the most recent most detailed description of criteria was included. Criteria for PRBC were reported by 17 unique groups; 13 in civilian and 4 in military practice. Hypotension was the most common trigger for PTRBC. Eight  articles used a systolic blood pressure ≤90 mmHg to initiate PTRBC (6 as major, 2 as minor criterion), 3 groups used a SBP ≤80 mmHg (major criterion), 1 group SBP ≤100 mmHg (minor criterion), and 4 groups an absent radial pulse (3 as major, 1 as minor criterion). A heart rate ≥ 120/min was used by 4 groups (3 major, 1 minor criterion). Clinical signs of poor perfusion, including changes in mental status (3 as major criterion), changes in skin colour (e.g. pallor, mottled)(2 as major criterion), or a prolonged capillary refill time (2 major) were also common criteria. The type of injury was a transfusion trigger for 9 groups, although the exact criteria varied: penetrating (truncal) wounds, proximal amputations or poor control of bleeding were used to initiate PRBC. 3 groups transfused RBC in case of traumatic cardiac arrest. Finally, in 7 out of 17 reports, clinicians were explicitly allowed to initiate transfusion based on their clinical judgement independently of other criteria.

Conclusion: Hypotension and tachycardia are commonly used as transfusion triggers in the prehospital setting, however, the exact criteria vary among EMS systems. Signs of poor tissue perfusion, the pattern of injuries and the clinician’s judgement may also guide the decision to initiate PTRBC. The results will be used to develop a consensus based prehospital transfusion protocol.