Cessation of Vital Signs Monitored During Lethal Hemorrhage: a Swine Study

Introduction: Two challenges of trauma triage are to identify wounded who are in danger of imminent death and to enable medics to determine if resuscitation is possible when making ?dead or alive? decisions on the battlefield. Hemorrhagic shock is the leading cause of death in combat injuries. The purpose of this study was to establish the sequence of vital sign cessation during lethal hemorrhage in swine. Our hypothesis was that brain electrical activity (electroencephalography [EEG]) and respiration are earlier indicators of imminent death than traditional modalities measured during triage, such as heart electrical activity (electrocardiography [ECG]) and blood pressure.

Methods: Lethal hemorrhage was induced in anesthetized Yorkshire pigs. Vital sign modalities measured were respiration, heart electrical activity (ECG), heart sound, blood pressure (systemic arterial pressure), and brain electrical activity (EEG).

Results: The sequence of vital sign cessation was (1) respiration, (2) brain electrical activity (EEG), (3) heart sound, (4) blood pressure, and (5) heart electrical activity (ECG). Cessation of respiration occurred at approximately the same time that brain electrical activity stopped (?flatlined?) for 2 seconds and then resumed briefly before cessation; cessation of heart electrical activity occurred almost 8 minutes later.

Conclusions: A 2-second EEG flatline and final respiration are useful event markers to indicate an opportunity to prevent irreversible brain damage from lethal hemorrhage. Since the 2-second EEG flatline and final respiration occur about 8 minutes before cessation of heart electrical activity (ECG), EEG and final respiration are earlier indicators of imminent death. The use of deployable noninvasive brain monitors implementing these findings can be live-saving on the battlefield as well is in civilian environments.