Pulmonary Gas Exchange During Hemodialysis: A Comparison of Subjects with and without COPD on Bicarbonate Hemodialysis

Abstract. Little is known about the effect of hemodialysis (HD) on gas exchange in subjects with chronic obstructive pulmonary disease (COPD). The purpose of this study was to examine blood gases and pH in COPD patients undergoing HD with bicarbonate dialysate. We studied thirteen subjects with COPD and thirteen controls (CON). All were dialyzed for 4 hrs against a bicarbonate HD solution. Blood gases, pH and HCO3- were initially analyzed (t0) and, during HD, at 30 min (t0.5), 1 hr (t1) and 4 hrs (t4). At t0, a statistically significant difference was observed for PO2 (CON: 84.7±3.60, COPD: 72.19±4.92; p<0.001). For the first hr, PO2 decreased, and at t1, oxygen was required for 6 COPD subjects. By t4, there was no significant difference in PO2 between groups. The alveolar-arterial gradient (ΔA-a) remained different between groups (P<0.001, all times), with increasing ΔA-a for both groups up to t1 and decreasing over the remaining 3 hr. For both groups, at t4, ΔA-a was higher than at t0 (p<0.001). For PCO2, both groups demonstrated increases from t0 to t1 (p=0.0004), with COPD having PCO2 higher than CON at t0.5 and t1 (p<0.05 for both); by t4, PCO2 levels decreased to nearly the same as at t0. Over the 4 hr treatment, HCO3- and pH increased significantly for both groups; however no significant difference was observed between COPD and CON. Markedly increased ΔA-a is observed during HD in some COPD patients. COPD patients retain more CO2. However, the effect of HCO3- leads to mild metabolic alkalosis at t4