Most prehospital medical interventions during civilian and military trauma casualty transport fail to utilize advanced decision-support systems for treatment and delivery of medical interventions, particularly intravenous fluids and oxygen. Current treatment protocols are usually based on standard vital signs (eg, blood pressure, arterial oxygen saturation) which have proven to be of limited value in detecting the need to implement an intervention before cardiovascular collapse. A primary objective of the US Army combat casualty care research program is to reduce mortality and morbidity during casualty transport from the battlefield through advanced development of a semiautomated decision-support capability for closed-loop resuscitation and oxygen delivery. To accomplish this goal, the Trauma Informatics Research Team at the US Army Institute of Surgical Research has developed two models for evidence-based decision support 1) a trauma patient database for capture and analysis of prehospital vital signs for identification of early, novel physiologic measurements that could improve the control of closed-loop systems in trauma patients; and, 2) a human experimental model of central hypovolemia using lower body negative pressure to improve the understanding and identification of physiologic signals for advancing closed-loop capabilities with simulated hemodynamic responses to hemorrhage. In the trauma patient database and lower body negative pressure studies, traditional vital sign measurements such as systolic blood pressure and oxygen saturation fail to predict mortality or indicate the need for life saving interventions or reductions in central blood volume until after the onset of cardiovascular collapse. We have evidence from preliminary analyses, however, that indicators of reduced central blood volume in the presence of stable vital signs include 1) reductions in pulse pressure; 2) changes in indices of autonomic balance derived from calculation of heart period variability (ie, linear and non-linear analyses of R-R intervals); and 3) reductions in tissue oxygenation. We propose that derived indices based on currently available technology for continuous monitoring of specific hemodynamic, autonomic, and/or metabolic responses could provide earlier recognition of hemorrhage than current standard vital signs and allow intervention before the onset of circulatory shock. Because of this, such indices could provide improved feedback for closed-loop control of patient resuscitation and oxygen delivery. These technological advances could prove instrumental in advancing decision-support capabilities for prehospital trauma care during transport to higher levels of care in both the military and civilian environments.