An assessment of the thermal safety of microwave warming of crystalloid fluids

We performed an in vitro study to determine the thermal safety of a domesti c microwave to warm intravenous crystalloid solutions. Five-hundred-millili tre bags of crystalloid, randomly allocated to groups which differed in pow er setting, timer setting and whether or not agitation was performed after warming, were heated in a microwave oven to a calculated temperature of 39 degrees C. Timer accuracy was checked by stopwatch. Bag temperature was mea sured using an infrared tympanic temperature probe and fluid temperature wa s measured with an in-line thermocouple. Mean times measured by stopwatch w ere higher than set. No in-line temperatures reached 40 degrees C. Wider ov erall. ranges and a higher mean were found with the tympanic probe compared with in-line temperature measurement. There were significant differences b etween the in-line temperatures of shaken and unshaken bags at each power s etting, but not when groups were added together. There was no change in col our or odour of bags or fluid. One bag developed a pinhole leak when the pa ckaging was removed.