Warming blood prior to transfusion using latent heat

Objective: Major trauma is associated with blood loss and hypothermia. It is common to replace lost fluid with red cells stored at 2–6°C, and/or colloid/crystalloid fluid stored at ambient temperature, thus increasing hypothermia risk. At trauma and medical retrieval sites, mains electricity powered fluid warmers cannot be generally used. Latent heat provides an alternate practical method of portable temperature-controlled intravenous fluid warming. This work investigates the safety and efficacy of a fluid warmer powered by latent heat. Methods: Twenty-five haematology patients received red cell transfusions, one through a fluid warmer, using latent heat from a super-cooled liquid and one without warming. Temperature of donor red cell units was measured after passing through fluid warmers. Blood samples were collected from red cell units and patients, prior and after each transfusion. These were tested for haemolysis markers (plasma haemoglobin, potassium, lactate dehydrogenase, bilirubin) and for traces of super-cooled liquid. Patient physiological parameters (oxygen saturation, pulse, temperature, blood pressure, respiration) were monitored during each transfusion. Results: Patient's physiological signs remained stable and no transfusion reactions were observed during warm transfusions. Latent heat fluid warmers increased the temperature of red cell units to approximately 35°C. There were no significant differences in haemolysis markers following warmed and unwarmed transfusions, and no contamination of red cell units by super-cooled liquid was detected. Conclusion: The latent heat fluid warmer was shown to safely warm transfused blood in a controlled clinical setting.