A microporous membrane oxygenator has been used in 258 clinical perfusions for cardiac surgery. In 132 perfusions the oxygenator was ventilated with 100% O2, and in 126 perfusions 98% O2-2%CO2 was used. Patients' BSA was 0.4-2.3 M2. Bypass duration was up to 563 min. In the group ventilated with 100% O2, average PaCO2 was 30 mmHg, with arterial pH of 7.48. 98% O2-2% ventilation resulted in an average PaCO2 of 36 mmHg, with arterial pH of 7.41. CO2 transfer is influenced by gas flow rate, and data from selected cases demonstrate that increasing gas flow results in decreasing PaCO2, while decreasing gas flow increases PaCO2. The thickness of the blood film is decreased by increasing the "shim" pressure, so that increasing the "shim" presure results in higher PaO2. Oxygen saturation averaged 99% for the entire series. Addition of CO2 to the oxygen and appropriate changes in gas flow and "shim" pressure permit changes to be made in the ventilation of the device during perfusion to achieve desired levels of PaO2 and PaCO2 under widely disparate conditions of temperature and flow.
A microporous membrane oxygenator which has transverse furrows on the membrane surface has been used in 50 clinical cardiopulmonary bypass procedures for coronary revascularization. The transverse furrows on the membrane, together with intermittent rapid pulsatile reversal of the blood flow in the blood film, produce secondary flows in the film and increase exposure of desaturated blood to the membrane. Venous drainage flows into a plastic reservoir, from which it is pumped through the oxygenator and integral heat exchanger into the aorta of the patient. Perfusions were carried out with hemodilution and moderate hypothermia. The oxygenator was ventilated with oxygen. In experimental perfusions using calves, the oxygen transfer was as high as 371 ml/min. During the clinical perfusions, arterial oxygen saturation was always 98% or higher. The mean arterial carbon dioxide tension was 41 mm Hg at a mean O2 flow of 1.4 L/min. The mean arterial pH was 7.40. The oxygenator puiser which created the secondary flows in the blood film was operated at a rate of between 90 and 255 pulses per minute. Pressure drop across the oxygenator averaged 18 mm Hg. Oxygen tension in the arterial blood could be regulated with the pulser rate, greater pulser rates being associated with larger oxygen transfer. Carbon dioxide transfer was best regulated by changes in gas flow rate. The oxygenator functioned well and was safe and reliable during these 50 perfusions.
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