Comparison of Four Stainless Steel Heat Exchangers for Neonatal ECMO Applications

Abstract

Conventional neonatal extracorporeal membrane oxygenation (ECMO) circuits utilize a heat exchanger distal to the oxygenator to replace ambient heat loss and maintain patient normothermia. A secondary function of the ECMO heat exchanger is to act as an arterial line bubble trap to protect the patient against accidental air embolism. Using an asanguinous recirculating test circuit, we measured and compared heat transfer properties, pressure drop, air trapping capabilities, and priming characteristics of four commercially available stainless steel heat exchangers currently being used in neonatal ECMO circuits: Avecor ECMOtherm, Gish HE-3, Gish HE-4, and Electromedics Dl079. Manufacturers' product specifications were also compared. The pressure drop across all four heat exchangers was less than 10 mmHg with flow rates up to 500 ml/min. The Gish HE-3 and HE-4 were the easiest to prime and de-air, while the Electromedics Dl079 was the most difficult. The heat exchangers with integral bubble traps (D1079 and HE-4) have superior air trapping capabilities. The ECMOtherm provided moderate air trapping capabilities(> 7.3 ml ± 1.5 ml) at flow rates under 300 ml/min. The low prime HE-3 was the poorest at trapping air; less than 1 ml at a 400 ml/min pump flow rate. Thermal analysis indicated that the D1079 had the highest performance factor, though all four heat exchangers had similar heat transfer rates and were capable of warming perfusate from 34° to 37°C on a single pass at pump flow rates of 500 ml/min. We conclude that all four heat exchangers can adequately maintain patient normothermia in neonatal ECMO applications. There are, however, significant differences in priming volumes, air trapping capabilities, and manufacturers' recommended maximum use time.