A comparison of a forced-air warming system to traditional thermal support for rodent microenvironments

Abstract

Thermal homeostasis is important for the well-being of laboratory rodents during experimental investigations involving chemical restraint. Anaesthesia-induced hypothermia may alter physiological processes, prolong recovery times, or result in death. Therefore, active warming may be needed to prevent excess heat loss from the rodent to the environment. Three methods of active warming were evaluated in typical rodent procedural areas and recovery cages: a forced-air warming system, infra-red heat emitter and circulating-water blanket. The first experiment involved recording the temperature of the immediate environment of the three devices, with and/or without the accompanying plastic drape, to simulate a surgical situation. In the second experiment, temperatures were recorded within cages that simulated a recovery situation with the same modalities. Forced-air warmer blankets (FAWB) were either wrapped around or placed underneath standard polycarbonate rodent cages and the results were compared with cage temperatures warmed by the heat emitter and circulating-water blanket. Temperatures were recorded at 0, 20, 40, and 60 min for each warming treatment, to determine mean temperature (+/- SEM) and the magnitude of increase (+/- SEM) between 0 and 60 min. All three devices showed an increase in temperature, but the FAWB with a plastic drape heated the procedural area microenvironment (Experiment 1) quickly and to a final temperature of 38.6 degrees C (101.5 degrees F) at 60 min, compared with 25 degrees C (77 degrees F) for the heat emitter and 28 degrees C (82.4 degrees F) for the circulating-water blanket. The magnitude of increase was significantly different for each treatment, but the FAWB with a plastic drape climbed 16.3 degrees C (29.3 degrees F) in 60 min. In Experiment 2, the FAWB wrapped around a cage, covered with a plastic drape, heated recovery cages to 32.5 degrees C (90.5 degrees F) compared to the heat emitter 26.4 degrees C (79.5 degrees F) and circulating-water blanket with drape 26.3 degrees C (79.3 degrees F). The magnitude of increase in the microenvironmental temperature was significantly higher for the FAWB, with the plastic drape wrapped around the recovery cage, compared to the other treatments. In both experiments, forced-air warming proved superior to the more traditional thermal support treatments in heating the microenvironments quickly and to an optimum ambient temperature. Forced-air warming devices should be considered when thermal support is required for rodent procedural areas and recovery cages.

Perioperative normothermia depends on intraoperative warming procedure, extent of the surgical intervention and age of the experimental animal

“…In a recent publication of Rembert et al (2004) it was clearly shown that the postoperative recovery of mice takes twice as long in a room with 18 8C ambient temperature compared to mice operated in a room with 26 8C. The ambient temperature in the animal facilities for the present study was 20.0 F 0.5 8C and it has to be taken into consideration whether a slightly increased ambient temperature would have an additional positive influence on the perioperative normothermia for the experimental animals in future studies.…”

“…Domitor is a sedative which acts through an alpha-2-receptor antagonistic pathway with analgesic and muscle relaxing characteristics. The use of a 2 -sedatives can impair the function of central thermoregulatory centers (Rembert et al, 2004). Thus, the anesthetic schedule (kind of anesthetics and time point of application) should have a major impact on the choice of the adequate warming system and temperature.…”

“…Pronounced uncontrolled hypothermia can be accompanied by an increased rate of heart cycle complications (Rembert et al, 2004) up to life-threatening conditions, both in humans and in experimental animals (Sessler, 1997;Lee et al, 2002;Matthew et al, 2002). There are various causes: extended surgical interventions with opening of body cavities (Elmore et al, 1998), the age of the patients (Reuler and Parker, 1978;Weinberg, 1993), inadequate intraoperative positioning (Elmore et al, 1998;Kongsayreepong et al, 2002), inappropriate anesthesia and also an individual sensitive reaction to the anesthesia (Rembert et al, 2004) can all result in a low body temperature. A low ambient temperature (Danzl and Pozos, 1994), strong bleeding (e.g.…”

The mouse and the rat in surgical research. The anesthetic approach

“…Anesthesia of small rodents is particularly challenging mainly due to hypothermia, high metabolic rate and the lack of reliable clinical signs of respiratory and cardiovascular functions (Rembert et al, 2004), highlighting the importance of pre-anesthetic evaluation. This evaluation entails a thorough clinical assessment of the animal and precedes the delivery of anesthetic care for surgery.…”

An MRI-Compatible High Frequency AC Resistive Heating System for Homeothermic Maintenance in Small Animals

“…It is well-known that the thermoregulatory mechanisms in mice are suppressed during general anaesthesia [1–3]. This, in combination with their high body surface-to-mass ratio, makes them very susceptible to hypothermia and their temperature often drops by several degrees Celsius within a few minutes of the onset of anaesthesia [2, 4].…”