Haemodialysis-induced respiratory changes

Eight patients receiving maintenance haemodialysis were studied under six different dialysis protocols, comprising Cuprophan and polyacrylonitrile (PAN 15) membranes, each used with dialysate containing 40 mmol/l acetate, 30 mmol/l acetate or bicarbonate (35 mmol/l), all other constituents being identical. Blood and expired gas determinations as well as transfer factor (DLCO) measurements, serum acetate concentrations, and WBC counts were performed. Rapid reductions in arterial oxygen (PaO2) were observed with Cuprophan (P less than 0.001), and with both strengths of acetate. Polyacrylonitrile used with acetate also demonstrated reductions in PaO2 but these were less severe than those observed with Cuprophan. Bicarbonate buffer resulted in a reduction in the severity of hypoxaemia, but failed to totally eliminate its occurrence. Hypoventilation was observed with both strengths of acetate dialysates, but not with bicarbonate. The respiratory exchange ratio decreased by 25% as a result of decreases in lung CO2 excretion when using acetate. Transfer factor declined by 40% for Cuprophan compared with 14% with polyacrylonitrile (P less than 0.01). Leucopenia was more severe with Cuprophan than with polyacrylonitrile. We conclude that amelioration of hypoxaemia may be achieved by the use of bicarbonate, but its cause is multifactorial, with contributions from hypoventilation secondary to dialyser CO2 losses and pulmonary dysfunction due to leucostasis. These observations suggest that the treatment of patients who have compromised cardiovascular function is most optimal with the use of biocompatible membranes which induce minimal leucopenia, used in conjunction with dialysate that utilises bicarbonate as the base replacement.