A physiological comparison of flutter valve drainage bags and underwater seal systems for postoperative air leaks.

BACKGROUND A study was undertaken to compare the relative physiological effects of underwater seal (UWS) versus flutter valve (FV) pleural drainage systems in the treatment of postoperative air leaks. METHOD Fourteen patients with air leaks of 1-11 days duration, following lobectomy (n = 5), bullectomy (n = 4), decortication (n = 4), and pleural biopsy (n = 1) were analysed. Intrapleural pressure (IPP) measurements were made using an in-line external strain gauge connected directly to the intercostal tube. Patients were connected simultaneously to both UWS and FV drainage systems and pressures were measured sequentially, isolating each system in turn. Maximum (IPPmax) and minimum (IPPmin) intrapleural pressures were calculated from graphic traces. The degree of lung expansion was recorded by chest radiography. RESULTS At resting tidal volume IPPmax was significantly higher with the UWS system (mean difference 0.8 mm Hg, 95% CI 0 to 1.6, p = 0.046) and IPPmin was significantly lower with the FV system (1.8 mm Hg, 95% CI 0.3 to 3.3, p = 0.023). The lung was fully expanded in 50% of patients at the time of study. The mean difference in IPPmin between systems was significantly increased when the lung was fully expanded (mean 2.8 mm Hg, 95% CI 0.1 to 5.5, p = 0.042). The mean difference in IPPmax was not affected by the degree of lung expansion (0.79, 95% CI -0.83 to 2.4, p = 0.31). CONCLUSION The results of this study suggest that, when postoperative air leak exists without a persistent pleural space, the flutter valve may provide a physiologically more effective alternative to the underwater seal drainage system.