CARDIAC CONTRACTILITY AND BLOOD-FLOW DISTRIBUTION FOLLOWING RESUSCITATION WITH 7.5-PERCENT HYPERTONIC SALINE IN ANESTHETIZED DOGS

We examined the specific effects of 7.5% hypertonic saline (HTS) on myocardial performance and regional blood flow and compared the efficacies of HTS and lactated Ringer's solution (LR) for hypovolemic resuscitation. Studies were performed in anesthetized dogs subjected to rapid hemorrhage to decrease mean arterial pressure by 50% over 60 min. The animals were resuscitated with either HTS (n = 8) at 5 ml/kg or LR (n = 7) at a dose required for equivalent restoration of cardiac output. Cardiac contractility was assessed using the slope E(es) of the left ventricular end-systolic pressure-diameter relationship and regional blood flow was measured using radioactive microspheres. At 10 min after resuscitation, mean arterial pressure increased from 45.1 +/- 2.5 to 77.7 +/- 3.2 mmHg with HTS and 50.9 +/- 2.5 to 80.1 +/- 3.2 mmHg with LR. Resuscitation with either fluid caused significant increases in heart rate and similar decreases in vascular resistance. Cardiac contractility (E(es)) did not change significantly with LR, whereas with HTS, E(es) increased from 14.8 +/- 0.9 during hemorrhage to 19.4 +/- 1.6 as compared with a baseline value of 13.4 +/- 1.5 mmHg/mm. Hemorrhage decreased blood flow to various organs by 50% to 70% of baseline. Except for better improvement in splenic and hepatic perfusion with HTS, similar restoration of blood flow to the heart, muscle, skin, kidney, and jejunum was observed at 10 min after resuscitation with either fluid. In this animal model of rapid and severe hemorrhagic shock, HTS given at approximately one-sixth the volume of LR was equally effective in providing temporary restoration of hemodynamic function. Hypertonic saline provides circulatory support in the presence of an acute blood volume depletion by a combination of increased cardiac contractility, plasma volume expansion, and peripheral vasodilation.