RESPIRATORY DYSFUNCTION AND WHITE CELL ACTIVATION FOLLOWING CARDIOPULMONARY BYPASS - COMPARISON OF MEMBRANE AND BUBBLE OXYGENATORS

Objective. Cardiopulmonary bypass induces respiratory dysfunction post operatively, with activation of both the complement system and white c ells implicated, This study compared the effects of bubble and membran e oxygenators for cardiopulmonary bypass in terms of respiratory dysfu nction and markers of white cell activation and endothelial damage. Me thods. Fifty patients undergoing cardiopulmonary bypass were randomly allocated either membrane or bubble oxygenation. Respiratory function was assessed serially by arterial oxygen tension and alveolar-arterial oxygen gradient. Complement activation was measured by serial samplin g of serum C3a levels. White cell activation was assessed by serial me asurement granulocyte elastase; other markers investigated were levels of thromboxane B2, von Willebrand factor and malondialdehyde. All sam ple measurements were made preoperatively, early and late during bypas s, 4-6 h postoperatively and then on the 1st, 2nd and 6th postoperativ e day. All samples were corrected for haemodilution, and differences b etween groups tested non-parametrically. Results. In bath groups of pa tients there was a highly significant fall (P < 0.001) in arterial oxy gen tension accompanied by a highly significant rise (P < 0.0001) in a leveolar-arterial oxygen gradient at 18 h compared to preoperative val ues persisting until 6 days postoperatively. Levels of C3a increased s ignificantly in both groups at 10 min post bypass, increased further a t 60 mill peaking at 4-6 h post bypass. Granulocyte elastase serum lev els increased significantly at 10 mill postoperatively in both groups compared to control levels. remaining elevated till 48 h, but returnin g to control levels by 6 days. Then was a small difference (P < 0.04) between the groups at 4-6 h only, Levels of von Willebrand factor incr eased significantly at 60 min post bypass in both groups, remaining el evated 6 days postoperatively. Levels of malondialdehyde increased at 10 min post bypass, remaining elevated until 6 days post bypass. Throm boxane levels showed no significant changes. For all markers measured, there were no significant differences between the groups other than t hose already indicated. Conclusions. This study demonstrated marked re spiratory dysfunction, complement activation and white cell activation in patients undergoing cardiopulmonary bypass with either bubble or m embrane oxygenators. There was marked variability in the response of i ndividual patients with either oxygenation technique. but overall no s ignificant differences between the groups.