Optimization of venous return tubing diameter for cardiopulmonary bypass

Objective: To determine the optimal venous tubing diameter for adult cardio pulmonary bypass (CPB) to improve gravity drainage and to reduce priming vo lume. Methods: (A) Maximum bovine blood flow rates by gravity drainage were assessed in vitro for four different tubing diameters (1/2, 3/8, 5/16, 1/4 inch) with three different lengths and various pre- and afterloads. Based on the results of (A) and multiple regression analyses, we developed equati ons to predict tubing sizes as a function of target flows. (C) The equation s obtained in (B) were validated by ex vivo bovine experiments. (D) The cli nically required maximal flows were determined retrospectively by reviewing 119 perfusion records at Zurich University. (E) Based on our model (B), th e clinical patient and hardware requirements, the optimal venous tubing dia meter was calculated. (F) The optimized venous tubing was evaluated in a pr ospective clinical trial involving 312 patients in Hangzhou. Results: For a mean body surface area of 1.83 +/- 0.2 m(2), the maximal perfusion flow ra te (D) achieved with 1/2-inch (= 1.27 cm(2)) venous tubing was 4.62 +/- 0.5 7 1/min (range: 2.50-6.24 1/min). Our validated model (B,C) predicted 1.0 c m(2) as optimal cross-sectional area for the venous line. New tubing packs developed accordingly were used routinely thereafter. The maximal flow rate was 4.93 0.58 1/min (range: 3.9-7.0) in patients with a mean body surface area of 1.62 +/- 0.21 m(2). Conclusion: The new venous tubing with 1.0-cm(2 ) cross-sectional area improves the drainage in the vast majority of adult patients undergoing CPB and reduces the priming volume (-27 ml/m). Reduced hemodilution can prevent homologous transfusions if a predefined transfusio n trigger level is not reached. (C) 2001 Elsevier Science B.V. All rights r eserved.