Haemodynamic responses to hypotensive haemorrhage in conscious sheep with emphasis on renal and femoral blood flow.

Haemodynamic responses to slow (0.7 ml kg-1 min-1) haemorrhage were investigated in eight adult conscious sheep, fitted with permanent ultrasonic flow probes around the renal and femoral artery. The haemorrhage was continued until the mean systemic arterial pressure (MSAP) suddenly dropped to about 50 mmHg. The spontaneous recovery was followed for 60 min and then the blood was retransfused. A distinct fall in MSAP was obtained after 14.5 +/- 0.9 ml blood (kg body weight)-1 (24% of the estimated blood volume) had been removed, but the interindividual differences were rather large (range, 10.2-18.1 ml kg-1). Therefore, the haemodynamic responses during haemorrhage were related to the total bleeding volume and not to time or volume per kilogram body weight. Before 90% of the total haemorrhage volume had been removed, the MSAP decreased gradually, reaching statistical significance at 80% (P < 0.05). At end of bleeding the cardiac output (CO) had fallen from a pre-haemorrhage level of 4.7 +/- 0.2 to 2.9 +/- 0.2 1 min-1. Although the femoral blood flow (FBF) was largely unaffected by the haemorrhage, and thus increased as a fraction of CO, the total systemic vascular resistance was markedly increased during the post-haemorrhage period, indicating a longer lasting elevation of vascular resistance in other vascular beds. In spite of a concomitant marginal decrease in renal blood flow (RBF), the renal vascular resistance (RVR) was unchanged until 90% total haemorrhage had occurred. At the same time as blood pressure fell, RBF decreased markedly, concomitant with a transient increase in RVR, which was followed by a decrease towards basal levels.(ABSTRACT TRUNCATED AT 250 WORDS)