In our study, a maximum decrease of 5% (95% CI, −115% to 105%) was seen in PLT function as measured by PLT aggregometry and TEG® between the unwarmed control and the warmed samples, although the intertest variability was quite large for both the unwarmed and warmed PLTs. PLT aggregation becomes abnormal during storage,5,6 and our results suggest that warming the PLTs with this device does not cause further degradation in their function. However, a larger sample size would be required to definitively establish whether warming induced further degradation of PLT function. Also, as activated PLTs contribute to the pathogenesis of transfusion-related acute lung injury,7–10 perhaps through the formation of neutrophil extracellular traps,11 studying the impact of transit time through the warmer, flow rate, and temperature on the activation status of the warmed PLTs will also be important in determining their safety.
Some previous clinical studies that compared posttransfusion PLT counts demonstrated higher PLT counts (corrected for the dose of transfused PLTs and the patient’s body surface area) after transfusion of warmed PLTs,12–14 while others showed no difference in counts.15,16 The suggested mechanism for the improvement is that the spherical shape that the PLTs tend to adopt during routine storage at room temperature is reversed on warming, thereby facilitating longer in vivo survival and higher counts.17,18
Warming of PLTs before transfusion in the operating room will help to reduce the risk of hypothermia in the recipient. Typically, transfusing 4 to 5 PLT units has a volume of approximately 250 to 300 mL, which is similar to the volume of a single donor (apheresis) PLT unit. This volume is also approximately the same as that of a unit of red blood cells or 5% to 6% of the circulating blood volume of the average patient. Hence, by mass and temperature balance, assuming a total circulating blood volume of 5 L and assuming the specific heat of PLT units are the same as circulating blood, transfusing a 5-unit whole blood PLT dose that is stored at 22°C into a patient with a core body temperature of 37°C would decrease the temperature of the circulating blood volume by almost a full degree to 36.1°C.
A limitation of our study is the small sample size. However, after analysis of the data from the first 10 PLT units, and the lack of a clear difference in any of the measured variables, the decision was made to terminate the study so as not to divert more PLT units away from patient care. It is also possible that warming the PLTs caused damage to the PLTs in a way that was not measured in our tests; however, PLT aggregometry is the “gold standard” for PLT function measurement, and no difference between the control and warmed samples was observed. Our in vitro findings, as well as those from future in vitro studies as outlined earlier, can help inform the design of a clinical trial whereby the safety and efficacy of warmed PLTs are evaluated in patients undergoing surgery.
The purpose of this study was to analyze the effect of warming on PLT function. As no significant decrease was observed in any of the measured variables after warming in this small study, we suggest that the current practice of warming the PLTs before infusion to an intraoperative patient is safe, although studies on PLT activation after warming are needed.
a E-mail communication between Jonathan Waters and Kayne Ryan, U.S. Marketing Manager of Smiths Medical (St. Paul, MN), the company which now produces the Level 1(R) rapid transfuser. August 7, 2012.
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