Acid-base balance and respiratory response during biofiltration with polyacrylonitrile membrane

To further elucidate the mechanisms responsible for the hypoxemia we studied ventilation, pulmonary gas exchanges, blood gas pressures and exchanges of CO2-T, CO2-D and HCO-3 in six patients during AD and BD on 1 m2 cuprophan filter and during BF on 1.2 m2 polyacrylonitrile filter. Blood passing through the dialyzer lost 172.8 mM/h of CO2-T in AD, 149.2 mM/h in BF and gained 25.6 mM/h in BD. In AD VE, VA and PaO2 decreased significantly after 30 and 60 min., in BF for the whole duration of dialysis. PoO2 showed a significant decrease both in AD and BF after 60 min. In AD PaCO2 was significantly reduced after 120 and 180 min. All the above parameters remained unchanged in BD. VCO2 remained unchanged in all. VCO2 and R decreased both in AD and BF. However, when VCO2 was corrected for CO2 loss across the dialyzer, overall CO2 loss (ventilated plus filtered) and R returned to basal values. In AD, HCO-3 and pH fell in the first 120 min., while in BD and BF they increased from the beginning of dialysis. In AD hypoventilation, hypoxemia and inadequate correction of acid-base balance were due to the loss of HCO-3 across the filter. In BF also hypoventilation and hypoxemia were due to the loss of HCO-3 across the filter but the acid-base balance was adequately corrected by HCO-3 reinfusion. In BD, there was HCO-3 gain across the filter which induced a gradual correction of acid-base balance without impairment of ventilation.