End-tidal carbon dioxide monitoring to predict hypovolaemic shock and the subsequent need for blood transfusions in adult pre-hospital trauma patients: a systematic review

Introduction: Traumatic haemorrhage is a major cause of preventable death, and blood transfusion is a crucial component of damage control resuscitation. Several diagnostic strategies exist to anticipate hypovolaemic shock and subsequent blood transfusion requirements, but their pre-hospital utility is inconsistent. Capnography or end-tidal carbon dioxide (EtCO 2 ) measurement has received growing recognition for prognostic capability in metabolic, respiratory and cardiac disease. This systematic review examines EtCO 2 efficacy in predicting hypovolaemic shock and subsequent blood transfusion in pre-hospital adult trauma patients.The aims and objectives of this study were, first, to determine if early EtCO 2 measurement in pre-hospital adult trauma patients can reliably predict hypovolaemic shock and/or blood transfusion when compared to existing strategies and scoring tools and, second, to identify if an EtCO 2 predictive threshold can facilitate this. Methods: A systematic review following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines was conducted. Seven electronic databases were searched using relevant indexed terms and keywords. Inclusion criteria were adult (>13 years) trauma patients with suspected or confirmed haemorrhage and with early (pre-diagnostic) EtCO 2 data from mainstream or side-stream devices, as related in peer-reviewed publications. All articles (n = 1932) were double-blind screened at abstract and title, then at full-text stage by two reviewers. Issues were discussed by the authors. Critical Appraisal Skills Programme (CASP) tools were used. Findings were narratively synthesised. Results: Thirteen articles were included. Significant heterogeneity, quality limitations and inconsistent reporting hindered direct comparison of results. Nevertheless, 10 comparator strategies/tools were identified and most studies demonstrated EtCO 2 ’s efficacy in predicting hypovolaemic shock / blood transfusion, with thresholds below 35 mmHg consistently suggested as predictive. Conclusion: A universal definition for major blood transfusion is still lacking. Further research is needed to identify accurate markers of haemorrhage, including EtCO 2 as a potential predictor. A high index of suspicion for haemorrhage and need for blood transfusion is recommended for adult trauma patients with EtCO 2 levels below 35 mmHg (4.7 kPa).