IMPROVED OUTCOME WITH HYPOTENSIVE RESUSCITATION OF UNCONTROLLED HEMORRHAGIC SHOCK IN A SWINE MODEL


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Abstract

Recent animal studies have shown that aggressive saline infusion may produce significant mortality in models of moderately severe (20–30 mL/kg) uncontrolled hemorrhage. The postulated mechanism is an increase in hemorrhage that accompanies restoration of normal blood pressure. Although aggressive saline infusion and restoration of blood pressure appear indicated when hemorrhage is potentially lethal (40–45 mL/kg), we hypothesized that the attempt to restore blood pressure with aggressive saline infusion would not improve survival. This study used a swine model of severe uncontrolled hemorrhagic shock to compare the effects of resuscitation to mean pressures of 40 and 80 mm Hg. Twenty-four immature swine, each with a surgical steel aortotomy wire in place, were bled rapidly from a femoral artery catheter to a mean arterial pressure (MAP) of 30 mm Hg. The aortotomy wire was then pulled, producing a 4-mm aortic tear and free intraperitoneal hemorrhage. When the pulse pressure decreased to 5 mm Hg, saline infusion was begun at 6 mL/ kg/minute and continued as needed to maintain the following endpoints: group I (MAP = 40 mm Hg), group II (MAP = 80 mm Hg), and group III (no resuscitation). After a maximum saline infusion of 90 mL/kg, the infusate was changed to shed blood at 2 mL/kg/minute. Data were compared using analysis of variance and Fisher's exact test. One-hour survival was 87.5%, 37.5%, and 12.5% for groups I, II, and III, respectively. Intraperitoneal hemorrhage for the three groups was 8.2 mL/kg, 39.9 mL/kg, and 6.7 mL/kg. The amount of saline infused was 55.8 mL/kg in group I and 90 mL/kg in group II. We conclude that the attempt to restore normotension with aggressive saline infusion markedly increases hemorrhage volumes and fails to improve survival in the setting of severe uncontrolled hemorrhage. Maintenance of the hypotensive state with judicious saline administration causes less blood loss and may be preferable before definitive surgical repair of the bleeding site.

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