Preventing hypothermia: convective and intravenous fluid warming versus convective warming alone

doi:10.1016/S0952-8180(98)00049-X

Journal of Clinical Anesthesia

Volume 10, Issue 5, August 1998, Pages 380-385

Presented in part at the 4th American-Japan Anesthesia Congress, San Francisco, March 13–14, 1997.

https://doi.org/10.1016/S0952-8180(98)00049-X Get rights and content

Abstract

Study Objective: To test the hypothesis that warming intravenous (IV) fluids in conjunction with convective warming results in less intraoperative hypothermia (core temperature <36.0°C) than that seen with convective warming alone.

Design: Prospective, randomized study.

Setting: University affiliated tertiary care teaching hospital.

Patients: 61 ASA physical status I, II, and III adults undergoing major surgery and general anesthesia with isoflurane.

Interventions: All patients received convective warming. Group 1 patients received warmed fluids (setpoint 42°C). Group 2 patients received room temperature fluids (∼21°C).

Measurements and Main Results: Lowest and final intraoperative distal esophageal temperatures were higher (p < 0.05) in Group 1 (mean ± SEM: 35.8 ± 0.1°C and 36.6 ± 0.1°C) versus Group 2 (35.4 ± 0.1°C and 36.1 ± 0.1°C, respectively). Compared with Group 1, more Group 2 patients were hypothermic at the end of anesthesia (10 of 26 patients, or 38.5% vs. 4 of 30 patients, or 13%; p < 0.05). After 30 minutes in the recovery room, there were no differences in temperature between groups (36.7 ± 0.1°C and 36.5 ± 0.1°C in Groups 1 and 2, respectively). Intraoperative cessation of convective warming because of core temperature greater than 37°C was required in 33% of Group 1 patients (vs. 11.5% in Group 2; p = 0.052).

Conclusions: The combination of convective and fluid warming was associated with a decreased likelihood of patients leaving the operating room hypothermic. However, average final temperatures were greater than 36°C in both groups, and intergroup differences were small. Care must be taken to avoid overheating the patient when both warming modalities are employed together.

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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Postoperative hypothermia followed by shivering is a common phenomenon in patients undergoing surgery under anesthesia, and should be prevented and treated in postoperative patient care units. This study was conducted to investigate the effect of warmed serum injection on postoperative shivering and recovery period of patients operated under general and spinal anesthesia.
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To compare the effectiveness of arteriovenous anastomosis (AVA) vs heated intravenous fluid (IVF) rewarming in hypothermic subjects. Additionally, we sought to develop a novel method of hypothermia induction.
Eight subjects underwent 3 cooling trials each to a core temperature of 34.8±0.6 (32.7 to 36.3°C [mean±SD with range]) by 14°C water immersion for 30 minutes, followed by walking on a treadmill for 5 minutes. Core temperatures (Δtes) and rates of cooling (°C/h) were measured. Participants were then rewarmed by 1) control: shivering only in a sleeping bag; 2) IVF: shivering in sleeping bag and infusion of 2 L normal saline warmed to 42°C at 77 mL/min; and 3) AVA: shivering in sleeping bag and circulation of 45°C warmed fluid through neoprene pads affixed to the palms and soles of the feet.
Cold water immersion resulted in a decrease of 0.5±0.5°C Δtes and 1±0.3°C with exercise (P < .01); with an immersion cooling rate of 0.9±0.8°C/h vs 12.6±3.2°C/h with exercise (P < .001). Temperature nadir reached 35.0±0.5°C. There were no significant differences in rewarming rates between the 3 conditions (shivering: 1.3±0.7°C/h, R² = 0.683; IVF 1.3±0.7°C/h, R² = 0.863; and AVA 1.4±0.6°C/h, R² = 0.853; P = .58). Shivering inhibition was greater with AVA but was not significantly different (P = .07).
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^☆: Supported by the MetroHealth Foundation, Chester Summer Scholar Program, Cleveland, OH; and SIMS-Level 1 Technologies, Keene, NH.

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Original ContributionsPreventing hypothermia: convective and intravenous fluid warming versus convective warming alone☆

Abstract

Introduction

Section snippets

Materials and methods

Results

Discussion

Acknowledgements

Anesthesiol Clin No Am

Lancet

J Clin Anesth

J Clin Anesth

Br J Anaesth

Hypothermia in the elderly

Int Anesthesiol Clin

Perioperative normothermia to reduce the incidence of surgical-wound infection and shorten hospitalization

N Engl J Med

Perioperative maintenance of normothermia reduces the incidence of morbid cardiac eventsa randomized clinical trial

JAMA

The catecholamine, cortisol, and hemodynamic responses to mild perioperative hypothermia. A randomized clinical trial

Anesthesiology

Hypothermia in adult trauma patients. Anesthetic considerations. Part II. Prevention and treatment

Am J Anesthesiol

Continuous arteriovenous rewarmingexperimental results and thermodynamic model simulation of treatment for hypothermia

J Trauma

Paradoxical inhibition of decreases in body temperature by use of heated and humidified gases [Letter]

Anesth Analg

Original Contributions
Preventing hypothermia: convective and intravenous fluid warming versus convective warming alone☆