Enalaprilat Improves Systemic and Mesenteric Blood Flow During Normotensive Resuscitation from Hemorrhagic Shock in Dogs

Abstract

Resuscitative interventions that improve systemic and mesenteric perfusion without causing instability in systemic arterial pressures may be helpful for improving trauma patient outcomes. Blocking angiotensin II formation with enalaprilat may be such an intervention. In this study involving resuscitation fiom hemorrhagic shock in dogs, the systemic and mesenteric cardiovascular effects of administering enalaprilat during resuscitation were investigated. Thermodilution-based and ultrasound-based methods of monitoring the systemic blood flow were also examined. Animals were hemorrhaged to a mean arterial pressure (MAP) of 40-45mmHg for 30min then 30-35mmHg for 30min followed by resuscitation with intermittent lactated Ringer's solution (200ml/kg/hr during first 4Omin, 60ml/kg/hr during following 130min) to reach and maintain a mean arterial pressure of 75-80mmHg for 170min. A constant rate infusion of saline vehicle with or without enalaprilat (0.02mgkglhr) was initiated after 40min of resuscitation. Systemic and mesenteric blood flows declined with hemorrhage, increased in all dogs with resuscitation, and then declined during the initial 40min of resuscitation. Enalaprilat administration resulted in increases in systemic and mesenteric blood flows not seen in the controls. The greater flows with enalaprilat appeared to be due to prevention of the increases in afterload noted in the controls. Comparison of monitoring techniques, showed stronger correlation between the ultrasonically determined descending thoracic aortic blood flow and celiac artery flow than between thermodilution determined cardiac output and celiac artery flow. It can be concluded that administration of a constant rate infusion of enalaprilat during resuscitation can be used to improve systemic and mesenteric blood flow and that passive methods of monitoring systemic blood flow, such as transesophageal ultrasound, may more accurately represent flow parameters than do bolus requiring methods, such as intermittent thermodilution.