Early Maladaptive Cardiovascular Responses are Associated with Mortality in a Porcine Model of Hemorrhagic Shock.

BACKGROUND: Hemorrhage is a leading cause of death on the battlefield. Current methods for predicting hemodynamic deterioration during hemorrhage are of limited accuracy and practicality. During a study of the effects of remote ischemic preconditioning in pigs that underwent hemorrhage, we noticed arrhythmias among all pigs that died before the end of the experiment but not among surviving pigs. The present study was designed to identify and characterize the early maladaptive hemodynamic responses (tachycardia in the presence of hypotension without a corresponding increase in cardiac index or mean arterial blood pressure) and their predictive power for early mortality in this experimental model. METHODS: Controlled hemorrhagic shock was induced in 16 pigs. Hemodynamic parameters were monitored continuously for 7 h following bleeding. Changes in cardiovascular and laboratory parameters were analyzed and compared between those that had arrhythmia and those that did not. RESULTS: All animals had similar changes in parameters until the end of the bleeding phase. Six animals developed arrhythmias and died early, while 10 had no arrhythmias and survived longer than 6 h or until euthanasia. Unlike survivors, those that died did not compensate for cardiac output (CO), diastolic blood pressure (DBP), and stroke volume (SV). Oxygen delivery (DO2) and mixed venous saturation (SvO2) remained low in animals that had arrhythmia, while achieving certain measures of recuperation in animals that did not. Serum lactate increased earlier and continued to rise in all animals that developed arrhythmias. No significant differences in hemoglobin concentrations were observed between groups. CONCLUSIONS: Despite similar initial changes in variables, we found that low CO, DBP, SV, DO2, SvO2, and high lactate are predictive of death in this animal model. The results of this experimental study suggest that maladaptive responses across a range of cardiovascular parameters that begin early after hemorrhage may be predictive of impending death, particularly in situations where early resuscitative treatment may be delayed.