The utility of a shock index ≥ 1 as an indication for pre-hospital oxygen carrier administration in major trauma

Abstract

Introduction and aims: The use of intravenous oxygen carriers (packed red blood cells (PRBC), whole blood and synthetic haemoglobins (HBOCs) for selected pre-hospital trauma resuscitation cases has been reported, despite a lack of validated clinical indications. The aim of this study was to retrospectively identify a sub-group of adult major trauma patients most likely to benefit from pre-hospital oxygen carrier administration and determine the predictive relationship between pre-hospital shock index (SI) [pulse rate/systolic blood pressure] and haemorrhagic shock, blood transfusion and mortality.

Methods: A retrospective review of adult major trauma patients recorded in The Alfred Trauma Registry was conducted. Patients were included if they received at least 1L of pre-hospital crystalloid and spent over 30 min in transit. The association of shock index and transfusion was determined. Patients were further sub-grouped by mode of transport to determine the population of trauma patients who could be included into prospective studies of intravenous oxygen carriers.

Results: There were 1149 patients included of whom 311 (21.9%) received an acute blood transfusion. The SI correlated well with transfusion practice. A SI ≥ 1.0, calculated after at least 1L of crystalloid transfusion, identified patients with a high specificity (93.5%; 95% CI: 91.8-94.8) for receiving a blood transfusion within 4h of hospital arrival. While patients transported by helicopter had higher injury severity and blood transfusion requirement, there were no difference in physiological variables and outcomes when compared to patients transported by road car.

Conclusions: A shock index ≥ 1.0 is an easily calculated variable that may identify patients for inclusion into trials for pre-hospital oxygen carriers. Shocked patients have high mortality rates whether transported by road car or by helicopter. The efficacy of pre-hospital intravenous oxygen carriers should be trialled using a shock index ≥ 1.0 despite fluid resuscitation as the clinical trigger for administration.

Keywords: Ambulance; Emergency; Pre-hospital; Resuscitation; Shock; Shock index; Synthetic haemoglobin; Transfusion; Wounds and injuries.