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Splanchnic circulatory adjustments during general anesthesia in man are difficult to assess in the absence of precise information regarding the depth of anesthesia and the regulation of gas exchange. The vasoconstriction responsible for the fall in hepatic blood flow that has been reported by several investigators (1, 2) may be attributable to the anesthetic agents themselves, to changes in venous return following reduction in activity and tone of skeletal muscles (3), to hypoxia or to hypercapnia. Of all of these the last has been particularly difficult to detect and control (4). Now, however, the availability of satisfactory muscle relaxants (5) and the development of mechanical devices for the maintenance of a suitable respiratory pattern (6) have made it possible to achieve constancy in anesthetic level, oxygenation, and carbon dioxide elimination. Comparable "steady state" measurements of splanchnic hemodynamic parameters can be made before and during hyper-capnia, because ventilatory excursion and rate can be fixed by artificial respiration after the administration of neuromuscular blocking agents, and the arterial carbon dioxide content can be altered as desired by appropriate changes in the breathing mixture. Under these circumstances, the volume of blood held within the splanchnic vasculature is determined only by local venomotor activity and by the balance between arteriolar resistances. Interference by variations in intra-abdominal pres-t Work done during tenure of a New York Heart Association fellowship. 1tWork done during tenure of a Life Insurance Medical Research Fund fellowship. sure that might otherwise arise from excessive and unpredictable movements of the diaphragm are eliminated. Data of value in elucidating the vascular response to hypercapnia and anesthesia may therefore be obtained from measurements of splanchnic blood volume as well as blood flow (7). In the study reported in this paper, mechanically controlled light anesthesia (thiopental-nitrous oxide) alone appeared to have no effect upon the splanchnic bed, suggesting that extraneous factors may have been influential in producing the changes previously ascribed to anesthesia. In contrast, hypercapnia was associated with splanch-nic vasoconstriction and with a reduction in splanchnic blood volume that was consistent with preponderant mesenteric and hepatic arteriolar constriction, splanchnic venoconstriction, or both. METHODS The subjects for this study were 19 patients (9 male and 10 female, between 21 and 60 years of age) from the Surgical Service of the Presbyterian Hospital. None presented clinical evidence of cardiovascular, renal, he-patic or biliary tract disease. Each was examined in the fasting state immediately prior to a …

the journal of clinical investigation/the journal of clinical investigation

THE EFFECT OF HYPERCAPNIA ON ESTIMATED HEPATIC BLOOD FLOW, CIRCULATING SPLANCHNIC BLOOD VOLUME, AND HEPATIC SULFOBROMOPHTHALEIN CLEARANCE DURING GENERAL ANESTHESIA IN MAN*