Combat stress or hemorrhage? Evidence for a decision-assist algorithm for remote triage

Introduction: In the setting of remote military triage, when physical access to the patient is not possible, traditional physiological measurements available to a combat medic may not differentiate between a wounded soldier and an active soldier. We tested the hypothesis that changes in high-frequency R-R interval spectral power (RRI HF) and pulse pressure (PP) would differ between progressive central hypovolemia (simulated hemorrhage) and exercise to evaluate their potential for remotely distinguishing active from bleeding soldiers. The RRI HF and PP were used because of their ability to track central hypovolemia. Methods: There were 12 (8 female/4 male) healthy, normotensive, non-smoking subjects (age 27 ± 2 yr; height 169 ± 3 cm; weight 68 ± 5 kg) who were exposed to progressive lower body negative pressure (LBNP) and a supine cycle ergometer protocol. ECG and blood pressure were measured continuously. Exercise workloads were determined by matching the heart rate (HR) responses to each LBNP level. Data were analyzed in time and frequency domains. Results: HR increased from 67 ± 3 bpm at rest to 101 ± 4 bpm by -60 mmHg LBNP and was matched within 5% during exercise. By the final stage, RRI HF decreased by a similar magnitude during both LBNP (-78 ± 7%) and exercise (-85 ± 6%). PP decreased by 30 ± 4% with LBNP compared with an increase of 20 ± 6% during exercise. Conclusion: Monitoring PP in combination with RRI HF would distinguish a bleeding from an active soldier. Technologies that incorporate telemetry to track these derived vital signs would provide a combat medic with remote decision support to assess soldier status on the battlefield.