Cerebral, coronary, and renal blood flows during hemorrhagic hypotension in anesthetized miniature swine

The purpose of these studies was to measure cerebral, coronary, and renal blood flow in miniature swine during hemorrhagic hypotension. Blood flows (BF) were measured in 16 anesthetized, female, miniature swine (35-50 kg) with the radiolabeled microsphere technique using 15-microns spheres. The animals were exposed to a standard, stepwise hemorrhagic shock protocol which set mean aortic pressure at 65, 50, 35, and 20 mm Hg for 10-15 min at each stage. Heart rate and aortic and central venous pressures were measured throughout these studies. Arterial pCO2, pO2 pH, and Hct were measured at the time of BF measurements. BFs were measured under baseline conditions and during three of the four stages of hypotension in each animal. BF was measured in the following tissues: brain (13 samples), heart (120 samples), kidney (left and right), spleen, liver, muscle, and skin. Coronary BF was consistently decreased during hypotension. Endo/Epi flow ratios were also decreased; however, they remained greater than or equal to 1.0. Renal BF and BF to most other tissues showed graded decreases with hypotension. Cerebral BF did not change significantly at any level of hypotension. The maintenance of cerebral BF in swine at such low arterial pressures (22 mm Hg) may be related to the decrease in central venous pressure (-8 mm Hg), which results in a delta P of 30 mm Hg, and/or to the swine's carotid rete mirabile.