Effects of Blood Flow Pulse Frequency on Mass Transfer Efficiency of a Commercial Hollow Fibre Oxygenator

The clinical advantages achievable through pulsatile blood perfusion during cardio-pulmonary bypass have recently suggested the design of new pulsatile systems for extracorporeal circulation. Still it is not clear whether current commercial membrane oxygenators could be adopted with such systems, since their behaviour with pulsatile perfusion has not been satisfactorily documented yet. In a previous paper, we assessed that pulsatile perfusion of a widely used hollow fibre oxygenator (Sorin® Monolyth) at 60 bpm provides more time-consistent oxygen transfer than steady perfusion. The present work is aimed to evaluate how the pulse frequency influences the gas transfer performance of the same device. The oxygenator was subjected to in vitro trials using a roller pump with pulsatile module (Stöckert Instrumente®) to generate pulsed flow. Four different pulse frequencies (45, 60, 75 and 90 bpm) were investigated at a fixed blood flow rate (4.0 l/min). The experiments lasting six hours were carried out using bovine blood with inlet conditions according to AAMI standards requirements. Blood samples were withdrawn every hour and O2 and CO2 transfer rates were evaluated. The experimental findings confirm that with pulsatile blood flow no time decay take place during prolonged perfusion. Moreover, when pulse frequency increases, transition levels occur for both O2 and CO2. Over these thresholds gas transfer rates display significant increases (p < 0.05), though of little magnitude (up to 2.5% for oxygen over 60 bpm; up to 3.7% for carbon dioxide over 75 bpm).