Abstract 143: The Modified Shock Index Separates Survivors from Non-Survivors in a Swine Model of Hemorrhagic Shock and Traumatic Brain Injury

Abstract

The ratio between heart rate and arterial blood pressure during hemorrhagic shock has been shown useful to identify individuals at risk of death. We herein compared the index using the systolic arterial pressure (SI) and using the mean arterial pressure (MSI) along with other measurements including cardiac index and lactate in a swine model of hemorrhagic shock and traumatic brain injury developed to model injury in the battlefield. The parent study was designed to compare three different types of vasopressin agonists with control solution while practicing fluid-restricted resuscitation. The present analysis included 60 experiments focused on the initial 240 minutes with induction of hemorrhagic shock by liver laceration removing approximately 1,000 ml of blood in 30 minutes. Eight animals died during the acute phase and compare to 52 survivors, they had higher (median, IQR) MSI (4.6; 3.3 - 5.4 vs 2.5; 2.0 - 3.1; p < 0.001), SI (2.7; 2.1 - 3.1 vs 1.8; 1.6 - 2.2; p < 0.001), lower cardiac index (2.8; 2.3 - 3.4 vs 3.7; 3.2 - 4.2; p < 0.001), but no differences in lactate levels. Three of the eight non-survivors (37.5%) and 42 of the 52 survivors (80.1%) received a vasopressin analog (p = 0.019). Compared to other measurements of hemodynamic stability, monitoring the ratio between the heart rate and mean arterial pressure is a feasible and practical approach to deploy in various out of hospital settings including the battlefield as well as in civilian trauma. This approach could also guide interventions including the use of vasopressor agents, which our studies demonstrate having a survival effect during acute bleeding caused by hemorrhagic shock.