Abstract 12: What Is the Optimum Preload Following Lethal Hemorrhagic Shock: Low-Volume Resuscitation---Less Is More
Introduction: We have tested whether improved outcomes occur with limited fluid volumes in a small animal model of hemorrhagic shock.
Methods: We placed carotid and femoral artery lines into 439 anesthetized, male Sprague Dawley rats. Rats were bled over 5 minutes to a targeted mean arterial pressure (MAP) of 30 mm Hg and maintained at this MAP for one hour by the withdrawal or replacement of heparinized blood. Animals surviving the one hour shock period were randomly assigned into six fluid groups and a no resuscitation control group. Resuscitation fluids were infused over ten minutes at 3:1 and 1:1 fluid to shed blood ratios. Resuscitated rats were observed for 2 hours, and the times to stop breathing, cessation of pulse, and MAPs recorded. M mode echocardiography was performed before instrumentation, ½ hour into shock, and 1 hour into resuscitation to determine end diastolic length (EDL), a marker of preload, and shortening fraction (SF), a marker of contractility. Data were analyzed by chi square analysis and Student’s t test.
Results: Only 86% of rats survived the shock period. Rats undergoing isotonic 1:1 resuscitation had improved survivals compared to animals undergoing 3:1 resuscitation (p=0.002). There was a trend for animals resuscitated with Lactated Ringers to have improved survival in the first hour in the 3:1 resuscitation groups. All non-resuscitated animals died. The EDLs and SFs of all animals were significantly reduced during shock (p<0.001). The 3:1 resuscitation increased the EDLs more than the 1:1 resuscitation, but EDLs in both fluid resuscitation groups never returned to initial levels (p<0.001).
Conclusion: The 1:1 fluid resuscitation was superior to 3:1 resuscitation in this hemorrhagic shock model. This suggests that the physiologic derangements in hemorrhagic shock are more complex than simple preload volume deficits,as although the 3:1 resuscitation had increased EDLs and presumably increased preloads, the 3:1 animals had poorer survivals.
- © 2012 by American Heart Association, Inc.