The Arterial Oxygen Extraction Tension and Oxygen Compensation Factor during Acetate and Bicarbonate Dialysis

Abstract

Recently introduced algorithms for determination of the arterial oxygen extraction tension (p_x), oxygen compensation factor (Q_x), total oxygen concentration, p 50 and erythrocyte 2,3-diphosphoglycerate (cDPG) concentration were applied and compared in 10 patients on acetate and bicarbonate dialysis. The oxygen extraction tension and cardiac oxygen compensation factor are new parameters for estimating the risk of peripheral tissue hypoxia. p_×was reduced to the same level (acetate 4.3 pKa vs. bicarbonate 4.3 pKa), whatever the mode of dialysis and changed only on acetate dialysis. The Q_xwas at baseline within normal (acetate 1.3 vs. bicarbonate 1.8), increased in acetate dialysis, but fell in bicarbonate dialysis. During acetate dialysis tissue oxygen supply fell and was not fully compensated by increasing Q_x, whereas during bicarbonate dialysis Q_xtended to fall without change in p_xindicating a better oxygen delivery to peripheral tissue.Hypoxia was observed independent of the dialysate bath. Isocapnia was observed during acetate dialysis, but pCO₂increased significantly using bicarbonate dialysate (p < 0.001). pH increased significantly (p < 0.001) during bicarbonate dialysis. Calculated in vivo p50 (acetate 3.8 pKa vs. bicarbonate 3.9 pKa) was slightly elevated in acetate dialysis partly due to the metabolic acidosis and in bicarbonate dialysis due to an increased cDPG concentration. After 30 min of bicarbonate dialysis a decrease was observed in p50, but improved during treatment reaching baseline level at the end of dialysis. p50 in acetate dialysis decreased steadily during the initial 3 h of treatment regaining baseline level before the end of dialysis. The predialysis level of cDPG (acetate 5.4 mmol/l vs. bicarbonate 6.9 mmol/l) was elevated, declined in bicarbonate dialysis within 30 min, but increased to baseline level. In acetate dialysis the cDPG changes paralleled the changes in p 50. The algorithms are based on approximations and therefore give approximate values, but they are in keeping with previously reported values of/; 50 and cDPG. They add new information about peripheral tissue hypoxia. Thus, the algorithms leave us with a useful and informative tool in getting reliable information on the state of the patient.