Clinical Trials of a New Low Prime Hollow Fiber Membrane Oxygenator

_____________ _ A new membrane oxygenator has been introduced by Travenol Laboratories with continued development carried out by Sarns Inc. The polypropylene hollow fibers are wound in a pattern perpendicular to the blood flow path and serve as the conduit for the ventilating gas. The membrane surface area is 1.8 M2. The device contains an integral stainless steel bellows heat exchanger and a temperature probe well built into the blood outlet. The oxygenator is held by a wire frame holder that can be mounted in any direction on the heart lung machine. A selection of various size collapsible PVC venous reservoir bags is available to meet individual patient needs. The venous inlet connector of the bag contains a temperature probe port and a connector for the cardiotomy drain line as well as a recirculation line that attaches to the oxygenator. Twenty consenting adult patients undergoing either CABG or valve replacement were perfused using this oxygenating system. The largest patient had a BSA of 2.3 M2 while the smallest was 1.48 M2. The mean patient size was 1.92 M2. For patients 2.0 M2 or larger, a one liter reservoir bag was employed requiring a total system prime of 2.0 liters. For the remaining patients, a 500 ml bag and 1.75 liters of prime were used. In all but one case, the prime consisted of 500 ml of HES and the balance, Lactated Ringers to which was added 500 units heparin per liter of total prime. The remaining case utilized four units of fresh frozen plasma as a substitute for the HES and for 500 ml of the Lactated Ringers. The blood gas results were very consistent and showed a very strong correlation between Fi02 setting, BSA, blood temperature and p02. The PaC02 was easily controlled to achieve alpha-stat by ventiDirect communications to: James P. Dearing, ECT Program, Medical University of South Carolina, 171 Ashley Ave., Charleston, SC 29425 lating the oxygenator at the optimal ventilation rate. Results include an average Pa02 of 137 mmHg with a mean 0 2 transfer of 104 ml per minute and a maximum transfer of 244 ml per minute. There were no gas exchange nor acid-base problems. The heat exchanger performance was satisfactory. The mean elevation in plasma hemoglobin was 19 mg/dl. The average decrease in platelet count was 37% while the hemodilutional hematocrit decrease was 26%. These data indicate that the oxygenator's blood handling characteristics compare favorably to other membrane oxygenators. Introduction ______________ _ The earliest configuration of hollow fiber membrane oxygenator suggested in the literature was one utilizing silicone rubber capillary tubing reported by Bodell, et al in 1962. 1 Because of the compliance of the silicone rubber capillaries, the gas exchange characteristics changed as the pressure changed. For this reason, this early membrane lung was designed so that blood flowed on the outside of the capillaries while the gas flowed through them. With the advent of microporous polypropylene and the technology to produce this material in hollow fibers of small, controlled geometry, several manufacturers reversed the earlier design and produced hollow fiber membrane oxygenators that used the capillary lumen for the blood path and circulated the ventilating gas around the fibers. 2·3 This configuration produced smooth laminar flow through the oxygenator and resulted in devices capable of producing uniform results. These devices, however, require membranes of large surface area in order to oxygenate the blood. 4 For this reason, several new oxygenators have been produced with the gas flowing through the hollow fibers while the blood flows around the fibers. · The new Hollow Fiber Membrane Oxygenator (HFMO) designed by Travenol Laboratories with further development by Sarns Inc. is of the latter design.