In vitro evaluation of three intravenous fluid line warmers

• Autores: Rebecca A. Lee
• Localización: JAVMA: Journal of the American Veterinary Medical Association, ISSN-e 0003-1488, Vol. 244, Nº. 12, 2014, págs. 1423-1428
• Idioma: inglés
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• Resumen

  • Objective—To determine in vitro output temperature differences of 3 IV fluid warmers.

    Design—Prospective, randomized study.

    Sample—3 IV fluid warmers.

    Procedures—Warming capabilities of a distance-dependent blood and fluid warmer marketed for human and veterinary use (product A) and a veterinary-specific distance-dependent fluid warmer (product B) were compared at 0, 4, 8, and 12 cm from the device to the test vein and at flow rates of 20, 60, 100, 140, 180, 220, 260, and 300 mL/h with room temperature (approx 22°C) fluids (phase 1). The superior warming device was compared against a distance-independent IV fluid warmer (product C) with room temperature fluids at the same flow rates (phase 2). The effect of prewarmed fluids (38°C) versus room temperature fluids was evaluated with the superior warming device from phase 2 (phase 3).

    Results—In phase 1, product B produced significantly warmer fluids than product A for all flow rates and distances. Both distance-dependent devices produced warmer fluid at 0 cm, compared with 4, 8, and 12 cm. In phase 2, product B produced warmer fluid than product C at 60, 100, 140, and 180 mL/h. In phase 3, there was no significant benefit to use of prewarmed fluids versus room temperature fluids. Output temperatures ≥ 36.4°C were achieved for all rates ≥ 60 mL/h.

    Conclusions and Clinical Relevance—Product B had superior warming capabilities. Placing the fluid warmer close to the patient is recommended. Use of prewarmed fluids had no benefit. Lower IV fluid flow rates resulted in lower output fluid temperatures.

    The incidence of anesthetic-induced hypothermia in small animals has remained moderately consistent throughout the past 30 years. In 1973, Evans et al1 reported an incidence of 100%, and in 2012, Redondo et al2 reported an incidence of 97.4%. Numerous adverse effects related to prolonged recovery, postoperative complications, and death have been reported in veterinary and human medicine.1–7 Despite great medical advances in many aspects of veterinary and human medicine, anesthetic-induced hypothermia remains prevalent. There is a lack of veterinary information on combatting this problem.

    There are 3 stages of anesthesia-induced hypothermia.8–10 The first stage occurs within the first hour of general anesthesia and is characterized by a sudden temperature decrease of 1° to 5°C because of redistribution of heat from the body core to the periphery. The second stage occurs 2 to 4 hours after induction of anesthesia and results in a much slower linear decline of temperature because of the disparity between increased heat loss and decreased metabolic heat production of the anesthetized patient. The third stage occurs after approximately 5 hours of anesthesia, and temperature often stops decreasing during this phase. This thermal plateau reflects a steady state in which heat loss equals heat production.8–10 Given that the most profound decrease in temperature occurs early, within the first stage of general anesthesia, methods to combat hypothermia should be targeted at this first stage.

    Three basic types of warming methods include passive surface, active surface, and active core.11 Traditional passive surface methods include use of cotton blankets, surgical drapes, plastic sheeting, and bubble wrap. Active surface methods include use of circulating water blankets, forced-air delivery systems, and warming panels. Traditional passive surface and active surface warming devices fail to adequately restore normothermia once the first stage of hypothermia has occurred because of peripheral vasoconstriction.4,9,12–14 Studies15–17 reveal that active surface warming prior to anesthetic induction helps decrease the severity of the initial temperature decline in adult humans. Unfortunately, this is impractical in most veterinary patients. Thus, passive and active surface warming are suboptimal in maintaining normothermia in the first stage, and fluid warmers warrant further exploration.

    Two main categories of fluid warming devices are distance dependent and distance independent. Most distance-dependent devices enable the fluid line to be placed in an S-shaped channel through the heating plate. Temperature sensors that are in contact with the tubing control the heating and regulate effluent temperature. Distance-independent devices consist of disposable heat exchangers that have concentric tubes in which a heated fluid (usually water) passes through the outer wall of the tubing; simultaneously, the IV infusate flows through the inner tubing. Heat is transferred from the hot outer tubing through the wall of the tubing to the infusate. These devices work most efficiently when the flow of the heated water is higher than that of the IV fluid infusate. They also overcome the problem of in-line cool down by actively warming the patient's fluids to the patient connection.18–20 Despite technological advances and the need to prevent secondary anesthetic-induced hypothermia in veterinary medicine, no product has documented superiority. No in vitro or in vivo output temperature studies have compared the efficacy of currently available veterinary distance-dependent and distance-independent devices with the simultaneous evaluation of the wide range of anesthetic fluid flow rates for small animal patients. Additionally, studies have not concurrently investigated the effect of altering the location of distance-dependent devices or whether there is a benefit to use of prewarmed fluids in conjunction with a fluid warming device.

    The purpose of the study reported here was to compare the warming capabilities of commonly available IV fluid line warmers on the basis of in vitro output temperature differences at a variety of flow rates and distances and the use of room temperature (approx 22°C) fluids versus prewarmed fluids. We hypothesized that a distance-dependent blood and fluid warmera marketed for both human and veterinary use would be a superior warming device, compared with a distance-dependent fluid warmerb marketed for veterinary use only as a fluid warmer, because it is the more expensive of the 2 devices and has been used reliably in our hospital for many years. We also hypothesized that connecting the warming device closest to the catheter hub would result in warmer temperatures at all IV fluid flow rates and that the warmest output temperatures would be achieved with higher IV fluid flow rates. We also hypothesized that a distance-independent blood and fluid warmerc would be an even better warming device because of its distance-independent design properties and documented superiority in humans.20–22 We hypothesized that the addition of prewarmed fluids would result in the warmest output temperatures and that the use of a warming device would yield higher output fluid temperatures, compared with the use of room temperature or prewarmed fluids alone, because these are commonly used in clinical settings.23