Original ContributionsPreventing hypothermia: convective and intravenous fluid warming versus convective warming alone☆
Introduction
Hypothermia commonly occurs during general anesthesia because of redistribution of heat from the core to the periphery, decreased metabolic heat production, impaired thermoregulation, and heat loss to a cold operating room (OR) environment.1, 2 Because of the morbidity associated with intraoperative hypothermia such as increased blood loss and transfusion requirements, wound infections, prolonged hospitalization, and adverse cardiac outcomes,3, 4, 5 convective warming is often used intraoperatively to prevent cutaneous heat loss, maintain a thermoneutral environment, and transfer heat across the skin surface. Fluid warming is usually employed in conjunction with convective warming to prevent hypothermia3, 4, 5, 6, 7, 8 because of the high specific heat of water, 1 kcal/L/°C. It is estimated that the negative thermal balance of infusing 3 liters of 21°C crystalloid into a 37°C 70 kg adult patient is 48 kcal.9 This heat loss represents approximately 1 hour of heat production in an anesthetized adult and is sufficient to decrease body temperature by 0.75°C or more during general anesthesia with neuromuscular blockade.1, 10, 11
The purpose of this study was to test the hypothesis that the use of warmed intravenous (IV) fluids in conjunction with convective warming results in less intraoperative hypothermia (core temperature <36.0°C) compared with convective warming alone.
Section snippets
Materials and methods
The protocol was approved by the MetroHealth Medical Center Hospital Institutional Review Board, and informed consent was obtained from the patients. Sixty-one ASA physical status I, II, and III adults undergoing elective major gynecologic, orthopedic, and general surgery scheduled to last at least 90 minutes were studied. Exclusion criteria were emergency surgery, preoperative use of calcium channel blockers, head injury, preoperative sublingual temperature of greater than or equal to 38°C or
Results
Five patients were excluded from the study after randomization for the following reasons: surgeon’s request to turn off convective warmer (n = 1, Group 1), anesthesiologist’s decision to use enflurane instead of isoflurance (n = 1, Group 2), intraoperative bleeding and decision to use fluid warmer (n = 3, Group 2). In these last three patients, final blood loss was estimated at 2.7 L, 3.3 L, and 0.3 L, and final core temperatures were 36.5, 36.0, and 36.6°C, respectively.
The groups were similar
Discussion
Development of mild hypothermia is one of the most common intraoperative problems in anesthetized patients undergoing surgery.16, 17, 18 Hypothermia can have many adverse physiologic effects such as decreased drug metabolism, impaired coagulation, decreased immune response, myocardial ischemia, increased norepinephrine levels, peripheral vasoconstriction, and compensatory increased oxygen requirements during rewarming.2, 5, 7 Mild hypothermia also has been shown to increase the incidence of
Acknowledgements
The authors are greatly indebted to the Post-Anesthesia Care Unit Staff at MetroHealth Medical Center for their support, and Fran Hall for assistance with manuscript preparation.
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Supported by the MetroHealth Foundation, Chester Summer Scholar Program, Cleveland, OH; and SIMS-Level 1 Technologies, Keene, NH.