Hypoxemia during hemodialysis: Effects of different membranes and dialysate compositions

Abstract

Arterial oxygen tension (PaO2) and white blood cell (WBC) count decrease during hemodialysis (HD) when certain types of membranes are used. Two mechanisms, impaired gas exchange due to intrapulmonary leucostasis and alveolar hypoventilation, have been proposed. To gain more insight into their respective roles, gas exchanges were compared in 6 patients with terminal renal failure treated with HD using four different combinations: a membrane with or without effects on WBC count and dialysate with or without constant PCO2. At repeated intervals PaO2 and PaCO2 were measured, while expired gas volume was recorded and expired gas was samples instantaneously at the mouth and measured using a mass spectrometer, allowing the exact measurement of the alveolar-arterial oxygen gradient (AaDO2). The use of a cuprophan (CP) membrane was consistently associated with a rapid decrease in PaO2, WBC count and an increase in AaDO2 irrespective of the type of dialysate used. This was not observed when a polyacrylonitryl (PAN) membrane was used. The use of an acetate (AT) buffered dialysate was consistently associated with a delayed decrease in alveolar PO2, respiratory quotient, and mean inspiratory flow, irrespective of the type of dialyzer membrane used. In HD using a PAN membrane with constant PO2 in the dialysate no drop in WBC nor in PaO2 was observed. These results indicate that both mechanisms of hypoxemia can be elicited with a slightly different time sequence in the same patients and in various combinations, according to the type of membrane and dialysate used. Patients with a compromised cardiopulmonary function should preferentially be dialyzed with a biocompatible membrane and a dialysate in which the loss of carbon dioxide is prevented.