The Effect of Hemodialysis on Oxygen Transport in Chronic Uremics

Previous studies from our laboratory suggested a decrease in tissue oxygen delivered during hemodialysis of chronic uremic patients due to an increase in hemoglobin-oxygen affinity, i.e. decrease in P50. This current study was designed to determine whether the changes in cardiac index and/or tissue oxygen extraction could compensate for increases in hemoglobin-oxygen affinity previously observed, so that total tissue oxygen delivery was unchanged during hemodialysis. This study demonstrated in patients during a 6-hour hemodialysis that: 1) no change occurs in hemoglobin-oxygen affinity expressed as P50, with unchanging plasma inorganic phosphate and red blood cell pH; 2) increased extraction of oxygen from tissue, measured via (A-V) O2 difference compensates for decreased oxygen delivery due to decreased cardiac output; and although there was no demonstrable change in hemoglobin-oxygen affinity, it would appear that increased tissue extraction of oxygen via other mechanisms should be easily able to compensate for previously reported changes in P50.