Association between early prehospital photoplethysmography waveform features and subsequent hemodynamic changes in trauma patients

Introduction: Following an acute traumatic insult, compensatory physiological mechanisms maintain delivery of oxygen while also influencing the shape of photoplethysmography (PPG) waveforms. Few studies have investigated the utility of PPG waveforms captured in clinical settings in identifying patients in compensated shock. We hypothesized PPG waveform features measured early in the prehospital course in trauma patients with normal initial shock index (SI) would predict subsequent change in SI (ΔSI) and provision of live-saving interventions (LSI). Materials and Methods: We conducted a secondary analysis of adult trauma patients transported from the scene of injury by a critical care air medical transport service whose initial shock index measurements (SI; during the first 7 minutes of care) were normal (≤ 0.8). The primary outcome variable was defined as the change in SI (ΔSI max = mean SI in first 7 minutes of care – maximum of all subsequent SI measurements). We performed stepwise multivariable linear regression to determine the association between PPG features (mean first 7 minutes) and ΔSI max . As an exploratory analysis, we examined association between PPG waveform features and prehospital life-saving interventions (LSI). Results: We identified 1488 adult trauma patients with interpretable PPG waveform and vital sign data with normal initial SI calculations. In adjusted analysis, beat systolic amplitude, area under the curve (AUC) and back slope independently predicted ΔSI max . AUC and systolic amplitude were predictive of prehospital LSI. Conclusion: These data suggest that early prehospital PPG waveform features can predict subsequent hemodynamic change and LSI. This information is clinically relevant as it may guide critical prehospital and emergency department triage and treatment decisions.