The limits of bloodwarming: maximally heating blood with an inline microwave bloodwarmer

Bloodwarmers, mandatory for use in trauma resuscitation, are currently limited to a maximum temperature of 42 degrees C by the American Association of Blood Banks. Using newly available inline microwave bloodwarming technology, we sought to identify the maximal temperature to which blood may be safely heated.

Using an inline microwave bloodwarmer, we warmed refrigerated packed red blood cells to settings ranging from "Off" to 60 degrees C. We evaluated heated blood for changes in red cell structure and function by measuring hemoglobin/hematocrit, potassium, lactate dehydrogenase, plasma hemoglobin, blood smear, osmotic fragility, PO2, giving 50% O2 saturation, and hemoglobin electrophoresis.

Measures of hemolysis showed no increase above control until temperatures of 51 to 53 degrees C were achieved (p < 0.05). Red cell size remained unaffected until temperatures of 53 degrees C were achieved (p < 0.05). Osmotic fragility was not elevated until 60 degrees C (p < 0.05). PO2 giving 50% O2 saturation was low for all samples. Hemoglobin electrophoresis remained unchanged at all temperature settings.

An inline microwave bloodwarmer may be used to heat blood safely to 49 degrees C. Blood warmed to this temperature may significantly increase the amount of heat returned to the hypothermic trauma patient.