Organ blood flow and O 2 transport during hypothermia (27°C) and rewarming in a pig model.

NEW FINDINGS: What is the central question of this study? Absence of hypothermia-induced cardiac arrest is a strong predictor for a favorable outcome after rewarming. Nevertheless, detailed knowledge of preferences in organ blood flow during rewarming with spontaneous circulation is largely unknown. What is the main finding and its importance? In a porcine model of accidental hypothermia, we find, despite a significantly reduced cardiac output during rewarming, normal blood flow and O2 supply in vital organs due to patency of adequate physiologic compensatory responses. In critical care medicine, active rewarming must aim at supporting spontaneous circulation and maintain spontaneous autonomous vascular control.

ABSTRACT: Introduction : The absence of hypothermia-induced cardiac arrest is one of the strongest predictors for a favourable outcome after rewarming from accidental hypothermia. We studied temperature-dependent changes in organ blood flow and O2 delivery (DO2 ) in a porcine model with spontaneous circulation during 3h of hypothermia at 27°C followed by rewarming.

METHODS: Anesthetized pigs (n = 16, wt. 20 - 29 kg) were randomally assigned to one of two groups: 1) Hypothermia/rewarming (n = 10), immersion cooled to 27°C and maintained for 3h before being rewarmed by pleural lavage (PL); and 2) Time-matched normothermic (38°C) controls (n = 6), immersed for 6.5h, the last 2h with PL. Regional blood flow was measured using a neutron-labelled microsphere technique. Simultaneous measurements of DO2 and O2 consumption (VO2 ) were made.

RESULTS: During hypothermia, there was a reduction in organ blood flow, VO2 and DO2 . After rewarming, there was a 40% reduction in stroke volume (SV) and cardiac output (CO) causing a global reduction in DO2 ; yet, blood flow to the brain, heart, stomach, and small intestine returned to pre-hypothermic values. Blood flow in liver and kidneys was significantly reduced. Cerebral DO2 and VO2 returned to control values.

CONCLUSIONS: Following hypothermia and rewarming there is a significant lowering of DO2 due to heart failure. However, compensatory mechanisms preserve O2 transport, blood flow and VO2 in most organs. Still, these results indicate that hypothermia-induced heart failure requires therapeutic intervention.This article is protected by copyright. All rights reserved.