A continuous hemorrhage model of fatal hemorrhagic shock in swine

We studied the effect of bleed rate on survival time and hemodynamics in a continuous hemorrhage model of fatal hemorrhagic shock in lightly anesthetized swine. Fasted immature swine (12-16 kg) were sedated with intramuscular (i.m.) ketamine, endotracheally intubated, anesthetized with halothane (0.75%), nitrous oxide, and oxygen, and then prepared for experimentation by placement of a pulmonary artery thermodilution catheter, femoral arterial and venous catheters, and by splenectomy. After instrumentation, halothane was discontinued and sedation was maintained with nitrous oxide and intravenous lorazepam. Thirty minutes later, the animals were bled continuously at 1.0 ml/kg per min (n = 8, Group I) or 1.25 ml/kg per min (n = 8, Group II) by a roller pump connected to the femoral arterial catheter. Hemodynamic parameters were recorded every 15 min until death occurred. Mean survival time was 50.2 +/- 3.0 min in Group I and 39.8 +/- 3.2 min in Group II (P less than 0.001). There was a stepwise decrease in blood pressure and cardiac index consistent with progressive hemorrhagic shock. This model results in reproducible survival times with small standard deviations. Although the animals are lightly anesthetized and the experiments are performed acutely, the hemodynamic responses and survival times observed are similar to those reported in previous studies of chronically instrumented, unanesthetized swine. This model may be more practical than unanesthetized, chronically instrumented swine models for evaluating the effects of various interventions on survival time and hemodynamics in acute hemorrhagic shock.