Redistribution of cardiac output caused by opening of arteriovenous anastomoses by a combination of azaperone and metomidate

The effects of the butyrophenone, azaperone 5 mg kg-1 i.m. alone and after addition of the imidazole derivative metomidate 6 mg kg-1 i.v. were studied in eight conscious pigs. Fifteen minutes after administration of azaperone, systemic arterial pressure was reduced by 35% as a result of a 45% increase in systemic vascular conductance and 10% decrease in cardiac output (Q). After azaperone, 23% of the radioactive labelled microspheres (15 (SD 1) microns) injected into the left atrium were detected in the lungs as a result of opening of arteriovenous anastomoses (baseline 3%). The increase in arteriovenous anastomotic blood flow was at the expense of the nutritional (= capillary) channels. Flow to the brain was maintained, but that to the left ventricle decreased in parallel with the reduction in arterial pressure. Vascular conductance of most other organs, except the skin, increased or was maintained. The addition of metomidate had no effect on Q because an increase in stroke volume (by 30%) compensated for the decrease in heart rate. Systemic vascular conductance decreased, most noticeably in the brain, left ventricle and skeletal muscle. We conclude that azaperone alone and in combination with metomidate had only a moderate effect on Q, but caused a redistribution in favour of arteriovenous anastomoses.