[Warming resuspended erythrocyte concentrates with a new microwave device. In vitro results and clinical experiences in comparison with continuous flow warming].

Rapid warming of stored red cell concentrates demands a technique that provides careful treatment of the erythrocytes, reliability, simple handling, and prompt processing. The Fenwal BW-5, a dry-heat blood warmer, is a well-established blood heating device. However, its use is time-consuming and rather complicated. The newly developed Infusotherm 407 is a microwave blood warmer providing short prewarming time and easy handling, but its safe applicability for resuspended red cells had not previously been proven. MATERIALS AND METHODS. Using the disposable plastic Ery-Set Schiwa (100 ml NaCl 0.9%), 211 red cell concentrates were diluted; 115 were warmed by the Infusotherm 407 and 96 by the Fenwal BW-5. The age of the blood units ranged between 1 and 30 days and the volume between 300 and 350 ml after resuspension. The Infusotherm 407 produces pulsed high-frequency waves that are absorbed by the blood unit and transformed into heat. The swivelling mechanism of the rotating holder allows continuous mixing and uniform warming of the red-cell suspension. The blood temperature is registered on the bag's surface by a thermometer integrated in the rotating holder. At 32 degrees C, the warming process is stopped automatically. Within the Fenwal BW-5 a special plastic bag has to be fixed between two electrically heated thermostat-controlled plates. The bag contains the blood that is passing through in several coils. A constant working temperature is maintained by an electronic monitor system up to a blood flow of 150 ml/min. Several laboratory parameters, i.e. extracellular hemoglobin, potassium, lactate dehydrogenase, as well as mean erythrocyte volume (MCV) and osmotic fragility of the red cells were determined from samples prior to and after blood warming. Thus, apparent hemolysis, morphological changes, or discrete damage to the erythrocytes could be detected. RESULTS. We observed a slight elevation in hemolysis parameters after warming with both devices. The alterations were within the range for stored packed red cells given by the European Public Health Committee. MCV and osmotic fragility remained unchanged. We did not find any comparable data concerning diluted packed red cells for either of the devices. Our own results did not show any significant difference between the two methods of heating. DISCUSSION. From the literature, it is known that the erythrocytes of full-sized blood units with normal hematocrit are not damaged by microwave warming. In contrast, small blood units and undiluted packed red cells revealed considerable hemolysis and distinct changes in MCV and osmotic fragility.(ABSTRACT TRUNCATED AT 400 WORDS)