Fluid accumulation after closure of atrial septal defects: The role of colloid osmotic pressure

Abstract

OBJECTIVES Following paediatric cardiac surgery with cardiopulmonary bypass (CPB), there is a tendency for fluid accumulation. The colloid osmotic pressure of plasma (COP p) and interstitial fluid (COP i) are determinants of transcapillary fluid exchange but only COP p has been measured in sick children. The aim of this study was to assess the net colloid osmotic pressure gradient in children undergoing atrial septal defect closure. METHODS Twenty-three patients had interventional and 18 had surgical atrial septal defect closures. Interstitial fluid was harvested using a wick method before and after surgery with CPB with concomitant blood samples. COP was measured using a colloid osmometer for small fluid samples. Baseline COP was compared with data from healthy children. RESULTS COP p at baseline was 21.9 ± 2.8 and 21.4 ± 2.2 mmHg in the interventional and surgical groups, respectively, and was significantly lower than in healthy children (25.5 ± 3.1 mmHg) (P < 0.001). In the surgical group, the use of CPB significantly reduced COP p to 16.9 ± 2.9 mmHg (P < 0.001) and the colloid osmotic gradient [Î "COP (COP p â ' COP i)] to 2.9 ± 3.8 mmHg (P < 0.001) compared with interventional procedure. One hour after the procedure, COP i was 15.6 ± 3.8 mmHg and 9.9 ± 2.1 mmHg (P < 0.001) and the Î "COP was 5.4 ± 3.0 mmHg and 9.1 ± 3.1 mmHg (P < 0.003) in the interventional and surgical groups, respectively. CONCLUSIONS Baseline COP p and COP i were lower in atrial septal defect patients compared with healthy children. The significantly lower COP gradient during CPB may explain the tendency for more fluid accumulation with pericardial effusion in the surgical group. The increased COP gradient after CPB may represent an oedema-preventive mechanism.