Comparison between the effects of central and systemic hypertonic NaCl on hemodynamic responses to hemorrhage in sheep.

Effects of treatment with systemic hypertonic (1.2M, 4 mL kg-1) NaCl (SHTNa) on tolerance to hemorrhage, accompanying systemic hemodynamics, and regional blood flow were investigated in conscious sheep. The results were compared with those obtained in animals subjected to hemorrhage during intracerebroventricular (ICV) administration of hypertonic (.5 M, .02 mL min -1) NaCl (CHTNa). Corresponding bleeding during ICV infusion of isotonic saline served as control. All treatments were started 30 min before commencement of a slow (.7 mL kg-1 min-1) hemorrhage, which was continued until the mean systemic arterial pressure (MSAP) suddenly dropped to about 50 mmHg. To reach the distinct fall in MSAP significantly more blood had to be withdrawn in the CHTNa (27.8 +/- 2.2 mL kg-1, p < .05) than in the SHTNa group (21.5 +/- 1.7 mL kg-1), which in turn showed a significantly higher tolerance to hemorrhage than the controls (15.1 +/- .7 mL kg-1, p < .01). The hemorrhage-induced reduction of cardiac output (CO) below basal level was less pronounced in the CHTNa group, where also the posthemorrhage CO recovery was most rapid. Spontaneous recovery of MSAP after bleeding was equally improved in both treatment groups with the central venous pressure being significantly higher in the SHTNa group. The hemorrhage-induced fall in renal blood flow (RBF) was more pronounced in the CHTNa group, which also had an impaired posthemorrhage recovery of RBF. In comparison to the SHTNa and control groups the renovascular resistance was significantly higher in the CHTNa group already during the prehemorrhage infusion period.(ABSTRACT TRUNCATED AT 250 WORDS)