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Induced hypothermia and rewarming after hemorrhagic shock
Göran Heinius1, Andreas Wladis, Robert G Hahn
1Department of Surgery, Söder Hospital, Karolinska Institute, SE-118 83, Stockholm, Sweden.
Background:
Recent patient and animal studies have shown protective effects of hypothermia (HT) in traumatic brain injury and hemorrhagic shock. We have demonstrated a reduced stress level and a lack of additive hemodynamic effects of HT. The present work was undertaken to evaluate whether these effects persist during and after rewarming.
Methods:
Pigs were quickly exsanguinated of 40% of their individually calculated blood volume and randomized to HT (32.5 degrees C) or normothermia (controls). After 30 min of HT, rewarming to baseline temperature was initiated. All animals were followed for 7 h. Thrombolelastography was used to evaluate blood coagulation.
Results:
HT did not aggravate the hemodynamic signs of hemorrhagic shock. HT decreased the oxygen uptake, however, which reduced the oxygen extraction ratio to the prehemorrhage level (P < 0.05). Serum levels of potassium were transiently stabilized by cooling. Coagulation was slower, but blood clot strength was normal. HT also delayed fibrinolysis (P < 0.05). Rewarming reversed all physiological changes induced by HT including those involving the coagulation system.
Conclusions:
HT produced few hemodynamic effects in the presence of hemorrhagic shock, but created a surplus of oxygen in the core circulation. Blood clotting was delayed by HT.