Contribution of thebesian veins to the physiologic shunt in anesthetized man

The purpose of the present study is to quantitate the contribution of the thebesian veins to the total physiologic shunt in anesthetized man. The subjects were adults, free of septal defects, who were undergoing a variety of open-heart procedures for the correction of diseased valves. The studies were completed following thoracotomy but prior to the placement of catheters. Subjects were anesthetized, intubated, and ventilated with a constant-volume respirator. Prior to blood sampling 100% oxygen was administered for at least 3 min. Samples were simultaneously drawn from the left atrium and the aorta and analyzed for Po2 with a microelectrode which had been calibrated with tonometered blood. Only studies in which aortic Po2 exceeded 150 mm Hg were accepted. Pco2 and pH were also measured. From the difference in Po2 between left atrium and aorta the contribution of left ventricular thebesian veins to the physiologic shunt was calculated using a modification of the shunt equation. Values found ranged from 0.12 to 0.43% of the aortic flow. Mixed thebesian oxygen content was assumed to be 6 vol % in this calculation, but the value chosen can be shown not to be critical.