Comparison of warming methods for core temperature preservation during total knee arthroplasty using a pneumatic tourniquet

BACKGROUND: It is important to ensure that patients are normothermic during surgery. In total knee arthroplasty, the pneumatic tourniquet affects body temperature. We compared the ability of two warming devices to preserve core temperature in patients using a lower limb tourniquet under general anesthesia. METHODS: We included 132 patients with American Society of Anesthesiologists physical status I-II who were scheduled to undergo total knee arthroplasty. The patients were randomly divided into four groups (n = 33): group 1, without any heating method; group 2, with fluid warming; group 3, with forced-air warming; and group 4, with a combination of the two heating methods. After the induction of anesthesia, the esophageal and urinary bladder temperatures were monitored and recorded every 5 min before tourniquet deflation and every 1 min after tourniquet deflation. RESULTS: Before tourniquet deflation, compared with group 1, the odds ratios of groups 3 and 4 were less than 1. After tourniquet deflation, compared with group 1, the odds ratios of all groups using warming devices were less than 1. In particular, group 4 showed the largest hypothermia-preventive effect among the four groups. There was a significant correlation between esophageal temperature and bladder temperature before and after tourniquet deflation. CONCLUSIONS: After tourniquet deflation, a combination of a fluid warmer and forced-air warmer is the most effective method to prevent hypothermia, although either a fluid warmer or forced-air warmer alone could help to prevent hypothermia. Urinary bladder temperature changes correlate well with esophageal temperature changes throughout this operation.

Hemolysis of irradiated leukoreduced red blood cells during rapid warming: An in vitro experimental study

BACKGROUND: Although water chambers are often used as surrogate blood-warming devices to facilitate rapid warming of red blood cells (RBCs), these cells may be damaged if overheated. Moreover, filtered and irradiated RBCs may be damaged during the warming process, resulting in excessive hemolysis and extracellular potassium release. METHODS: Using hand-held syringes, each unit of irradiated and leukocyte-filtered RBCs was rapidly passed through a water chamber set to different temperatures (baseline before blood warming, 50℃, 60℃, and 70℃). The resulting plasma potassium and free hemoglobin levels were then measured. RESULTS: Warming RBCs to 60℃ and 70℃ induced significant increases in free hemoglobin (median [interquartile ranges] = 60.5 mg/dl [34.9-101.4] and 570.2 mg/dl [115.6-2289.7], respectively). Potassium levels after warming to 70℃ (31.4 ± 7.6 mEq/L) were significantly higher compared with baseline (29.7 ± 7.1 mEq/L; P = 0.029). Potassium levels were significantly correlated with storage duration after warming to 50℃ and 60℃ (r = 0.450 and P = 0.001; r = 0.351 and P = 0.015, respectively). CONCLUSIONS: Rapid warming of irradiated leukoreduced RBCs to 50℃ may not further increase the extracellular release of hemoglobin or potassium. However, irradiated leukoreduced RBCs that have been in storage for long periods of time and contain higher levels of potassium should be infused with caution.