DEFINING THE CRITICAL LIMIT OF OXYGEN EXTRACTION IN THE HUMAN SMALL-INTESTINE

Although animal models have been used to characterize the relation bet ween oxygen consumption and blood flow, reliable data have not been ge nerated in the human small intestine. We perfused segments of human sm all intestine by using an ex vivo perfusion circuit that allowed preci se manipulation of blood flow and perfusion pressure. Our goal was to define the critical level of intestinal blood flow necessary to mainta in the metabolic needs of the tissue. Human small intestine (n = 5) ti ssue obtained at transplantation harvest was transported on ice to the laboratory. A 40-cm mid-jejunal segment was selected for perfusion, a nd appropriate inflow and outflow vessels were identified and cannulat ed. Perfusion with an autologous blood solution was initiated through an extracorporeal membrane oxygenation circuit. After a 30-minute equi libration period, arterial and venous blood gases were measured at var ying flow rates while maintaining a constant hematocrit level. Arteria l and venous oxygen content, arteriovenous oxygen difference (A-VO2 di ff), and oxygen consumption (VO2) were then calculated. Our results de monstrated that at blood flows >30 ml/min/100 g, VO2 is independent of blood flow (1.6 +/- 0.06 ml/min/100 g), and oxygen extraction is inve rsely related to flow Below this blood flow rate of 30 ml/min/100 g, o xygen extraction does not increase further (6.3 +/- 0.3 vol%), and VO2 becomes flow dependent. This ex vivo preparation defines for the firs t time a threshold value of blood flow for small intestine below which oxygen consumption decreases (30 ml/min/100 g). Previous animal studi es have correlated such. a decrease in oxygen consumption with functio nal and histologic evidence of tissue injury. This ''critical'' flow r ate in human intestine is similar to that found previously in canine a nd feline intestine, but lower than that of rodent species.