Effect of moderate hypothermia in the treatment of canine hemorrhagic shock

This study evaluated a possible protective and therapeutic effect of moderate hypothermia in the treatment of severe hemorrhagic shock. A modified Wiggers shock preparation was used. Normothermic dogs (Group I, N = 6) were maintained at normal body temperature throughout hemorrhagic shock and resuscitation. In Group II, hypothermia was initiated after 15 minutes of hemorrhagic shock (N = 12) and maintained for 60 minutes after fluid resuscitation. Animals were then rewarmed with Group IIA (N = 7) receiving sodium bicarbonate to correct acidosis, while Group IIB (N = 5) did not; all dogs were studied for an additional 120 minutes. During shock heart rate was lower in both hypothermic groups (IIA and IIB) compared to normothermic dogs (85.0 ± 3.9, 77.7 ± 4.6 vs. 136.7 ± 4.2, respectively, p < 0.05), while +dP/dt (mmHg/s) remained stable in all dogs. Furthermore, pH was lower in the hypothermic (Groups IIA and IIB) compared to normothermic animals at this time period (Group IIA: 7.19 ± 0.02, Group IIB: 7.13 ± 0.02 vs. Group I: 7.24 ± 0.02). Arterial pCO₂ was higher in the hypothermic hemorrhagic shock Groups IIA and IIB compared to normothermic group (34.5 ± 2.2, 37.4 ± 2.2 vs. 20.3 ± 20, 3 ± 2.0, p < 0.05) due to hypothermia-depressed respiration. A higher myocardial O₂ consumption and a negative myocardial lactate balance occurred in the normothermic animals during hemorrhagic shock. After resuscitation and rewarming, stroke volume (mL/beat) and cardiac output (L/min) were lower in hypothermic animals with persistent acid-base derangements (12.6 ± 2.5, 1.3 ± 3.0, respectively) compared to hypothermic dogs with acid-base correction (20.1 ± 3.3, 2.2 ± 0.3) and normothermic dogs (24.6 ± 3.0, 3.0 ± 0.3, p < 0.05), while myocardial O₂ extraction and myocardial lactate production were higher. Results suggest hypothermia decreases the metabolic needs and maintains myocardial contractile function in hemorrhagic shock. Hypothermia may have a beneficial effect and, with normalization of acid-base balance, a therapeutic role in hemorrhagic shock.