The conundrum of the definition of haemorrhagic shock: a pragmatic exploration based on a scoping review, experts' survey and a cohort analysis

Purpose: Traumatic hemorrhagic shock (THS) is a complex, dynamic process and, no consensual definition of THS is available. This study aims (1) to explore existing definitions of traumatic hemorrhagic shock (THS), (2) to identify essential components of these definitions and (3) to illustrate in a pragmatic way the consequences of applying five of these definitions to a trauma registry.

Methods: We conducted (1) a scoping review to identify the definitions used for traumatic hemorrhagic shock (THS); (2) an international experts survey to rank by relevance a selection of components extracted from these definitions and (3) a registry-based analysis where several candidate definitions were tested in a large trauma registry to evaluate how the use of different definitions affected baseline characteristics, resources use and patient outcome.

Results: Sixty-eight studies were included revealing 52 distinct definitions. The most frequently used was "a systolic blood pressure (SBP) less than or equal to 70 mmHg or between 71 and 90 mmHg if the heart rate is greater than or equal to 108 beats per min". The expert panel identified base excess, blood lactate concentration, SBP and shock index as the most relevant physiological components to define THS. Five definitions of THS were tested and highlighted significant differences across groups on important outcomes such as the proportion of massive transfusion, the need for surgery, in-hospital length of stay or in-hospital mortality.

Conclusions: This study demonstrates a large heterogeneity in the definitions of THS suggesting a need for standardization. Five candidate definitions were identified in a three-step process to illustrate how each shapes study cohort composition and impacts outcome. The results inform research stakeholders in the choice of a consensual definition.