Skip to main content
NCBI home page
Canadian Journal of Veterinary Research logoLink to Canadian Journal of Veterinary Research
. 2021 Apr;85(2):106–111.

Pre-warming following premedication limits hypothermia before and during anesthesia in Sprague-Dawley rats (Rattus norvegicus)

Maxime Rufiange 1, Vivian SY Leung 1, Keith Simpson 1, Daniel SJ Pang 1,✉
PMCID: PMC7995546  PMID: 33883817

Abstract

In humans and other mammals, general anesthesia impairs thermoregulation, leading to warm core blood redistributing to the periphery. This redistribution is an important contributor to hypothermia that can be reduced with pre-warming before anesthesia. Additionally, sedation following premedication has been associated with hypothermia in dogs. In a prospective, randomized, cross-over study, 8 adult male and female rats (weighing 388 to 755 g) were sedated with intramuscular ketamine-midazolam-hydromorphone, then placed in an unwarmed cage or warmed box for 14 minutes, followed by 30 minutes of isoflurane anesthesia with active warming. Core body temperature was monitored throughout. After sedation, warmed rats gained 0.28°C ± 0.13°C and unwarmed rats lost 0.19°C ± 0.43°C, a significant difference between groups (P = 0.004). After anesthesia, warmed rats maintained higher core temperatures (P < 0.0001) with 2/8 and 6/8 of warmed and unwarmed rats becoming hypothermic, respectively. Pre-warming during sedation and active warming during general anesthesia is effective in minimizing hypothermia.

Introduction

Hypothermia occurs commonly during the perianesthetic period and is well-documented in humans and animal species (1–9). Thermoregulation is controlled through afferent signaling from temperature receptors dispersed throughout the body and integrated at the hypothalamus, resulting in physiologic and behavioral effects to maintain normothermia (10,11). At induction of general anesthesia, disruption of thermoregulation occurs, leading to a rapid decrease in core body temperature associated with redistribution of warm core blood to the periphery. This redistribution accounts for approximately 80% of the initial hypothermia occurring in the first hour of general anesthesia (12–14). Maintaining normothermia during the perianesthetic period is desirable because a small reduction, as little as 1°C in humans, can have significant deleterious effects. These include longer hospitalization time, increased blood transfusion requirement, surgical site infection, and discomfort (15–17). The evidence for similar adverse effects in animals is currently limited, although recovery following anesthesia is prolonged (2,18). Based on original studies in humans, previous work in laboratory rodents has shown that pre-warming (i.e., providing active heating before induction of general anesthesia) is effective at delaying the onset of hypothermia (7,19).

Unlike rodents housed in laboratories, rodents in veterinary clinics are often premedicated with drugs that cause sedation and reduced activity before induction of general anesthesia. It was previously shown that reduced activity leads to a reduction in temperature in dogs (1). To the authors’ knowledge, this has not been studied in rats.

The primary aims of this study were to identify if premedication lowers body temperature and if pre-warming instituted during premedication would prevent a temperature reduction. A secondary aim was to determine if the addition of pre-warming improved normothermia during maintenance of general anesthesia, during which external heat was provided. We hypothesized that premedication would be associated with a decrease in body temperature and that pre-warming would allow normothermia to be maintained both before and after induction of general anesthesia.

Materials and methods

Animals

Male (n = 3) and female (n = 5) Sprague-Dawley rats aged 32 wk (median; range: 15 to 34 wk) with a body mass of 507 g (range: 388 to 755 g) were obtained from a commercial supplier (Charles River Laboratories, Senneville, Quebec).

The ethics committee of the Université de Montréal, operating under the guidelines of the Canadian Council on Animal Care, approved the experimental protocol (18-Rech-1947).

Rats had an acclimation period of 7 d, which included exposure to the unheated warming box and daily handling. Rats were considered habituated when a treat (Honey Nut Cheerios; General Mills, Golden Valley, Minnesota, USA) offered by hand was readily accepted. All rats were pair-housed in a plastic home cage [45 (l) × 24 (w) × 20 (h) cm, 2154F; Tecniplast, Montreal, Quebec] containing wood chips (Beta Chip; Charles River Laboratories, Sherbrooke, Quebec) and shredded paper. Enrichment consisted of a polyurethane toy (Bio-Serv, Flemington, New Jersey, USA) and a plastic tube (ABS tubing; IPEX, Verdun, Quebec). Lights, humidity, and temperature were controlled: light/dark cycle 14/10 h (lights on at 6:00 am), 22 to 27% humidity, and temperature set at 22°C. Rats were provided a standard diet (Rodent Chow 5075; Charles River Laboratories, Saint-Constant, Quebec) along with treats offered ad hoc (Very Berry Supreme Mini-Treats, Veggie-Bites, and Fruit Crunchies; Bio-Serv). Water was offered ad libitum.

Sample size estimation was based on published data (7) indicating that 8 rats would be sufficient to identify a mean difference in core body temperature of 1°C with a standard deviation of 0.5°C. Alpha was set at 0.05 with a power of 80%.

Telemetric temperature capsule implantation

Intraperitoneal capsule implantation for telemetric temperature monitoring was carried out as part of another study (Anipill temperature sensor, Aniview system; Bodycap, Hérouville-Saint-Clair, France). Surgical implantation into the abdomen under general anesthesia was performed 11 to 13 wk before the current study began (19).

Perioperative temperature experiment

A prospective, randomized, cross-over study was designed with 2 treatment groups: warming box and unwarmed cage. Rats were randomized (www.random.org) to the first treatment group before the study began. Rats were alternated to the other treatment group after a minimum washout period of 5 d. Experimentation and data collection were performed by a single experimenter (MR), preventing blinding to treatment allocations and outcomes. Data were analyzed by a different experimenter (VL), unfamiliar with the study aims and not involved with data collection. Criteria for exclusion from the study consisted of a recorded core temperature < 27°C or > 41°C, the presence of cutaneous thermal injuries, or weight loss ≥ 2% over the 5 d following treatment. Experiments were conducted between 9:00 am and 5:00 pm.

To facilitate comparisons between treatment groups, individual core temperatures (sampled every 300 s the day before experimentation, from 8:00 am to 6:00 pm) were pooled and a hypothermia threshold was calculated (mean core temperature over the 10-hour sampling period minus 2 standard deviations).

The experimental timeline consisted of 5 phases: i) premedication injection (all rats); ii) warmed or unwarmed treatments (as per randomization); iii) intravenous (IV) catheter insertion; iv) general anesthesia and sham surgery preparation; and v) recovery. All animals received the same intramuscular (right quadriceps muscle) premedication, consisting of ketamine (Narketan 100 mg/mL; Vétoquinol, Lavaltrie, Quebec), 20 mg/kg body weight (BW), midazolam (5 mg/mL; Sandoz, Boucherville, Quebec), 0.5 mg/kg BW, and hydromorphone (2 mg/mL; Sandoz), 0.2 mg/kg BW. Immediately following injection, rats were either placed in an unwarmed home cage (contents identical to home cage but no other rat present; unwarmed group) or placed in a small warming box [25.7 (l) × 11 (w) × 10.7 (h) cm; Harvard Apparatus, Holliston, Massachusetts, USA] (warmed group). The warming box was pre-warmed to 31.3°C ± 1.0°C with a purpose-built heating unit (Vetronic Services, Abbotskerswell, England) before rat entry (confirmed with a calibrated infrared thermometer). Animals remained in the unwarmed cage or warmed box for a period of 14 min (time previously shown to allow an increase in core temperature of 1% when animals were warmed under similar conditions) (19,20). Following the elapsed time, rats were removed from the unwarmed cage or warming box and placed in sternal recumbency on a pre-warmed electrical heat pad (output set to 37°C) (16 × 38 cm rodent warmer with cage heating pad; Stoelting, Wood Dale, Illinois, USA) and IV catheterization was performed (coccygeal vein). General anesthesia was then induced via a nose cone connected to a Bain breathing system (isoflurane vaporizer set at 1.75%, 1 L/min oxygen). Rats were placed in dorsal recumbency and their abdomens were prepared by shaving their fur from the xyphoid process to the pubis, covering an area of 5.6 × 9 cm. This was followed by 3 passages each of gauzes soaked in isopropyl alcohol 70% and chlorhexidine gluconate 0.05% solution. General anesthesia was maintained for 30 min in total, with all animals lying on the heat pad in dorsal recumbency throughout this time. After 30 min, isoflurane was discontinued, and animals were allowed to recover on the heating pad until sternal recumbency was achieved. Animals were subsequently returned to their home cage.

Temperature monitoring

Core body temperatures were recorded every 2 min during the 14 min after injection until beginning the catheter placement. Temperature monitoring stopped during catheter placement and resumed during general anesthesia. Core temperature was monitored every 2.5 min during this period.

Statistical analysis

Data were analyzed using commercial software (Prism 8.1.2; GraphPad Software, La Jolla, California, USA and MedCalc Software 18.5, Ostend, Belgium). All data approximated a normal distribution according to the D’Agostino-Pearson Omnibus normality test. A paired t-test was used to compare groups for the time of IV catheter placement and sham surgery preparation. Unpaired t-tests were used to compare the areas under the curves during the 14 min after the sedation injection and during the 30 min of anesthesia. During the premedication phase, the mean difference from the temperature immediately before injection was calculated and analyzed. During general anesthesia, temperature data were binned at 2.5-minute intervals to account for small differences in times to begin general anesthesia after sham preparation was complete. The baseline values to calculate the area under the curve (AUC) were set as −0.4 and 35 for the periods after premedication injection and during anesthesia, respectively. P-values < 0.05 were considered significant. Data are presented as mean ± standard deviation in the text, with the 95% confidence interval (CI) of the mean difference. Data supporting the results are available in an electronic repository: https://doi.org/10.7910/DVN/MS4WUT

Results

No animals were excluded from the study; each group consisted of 8 rats. The mean core temperature of all rats during baseline (day before experimentation) was 36.9°C ± 0.27°C; therefore, a hypothermia threshold value of 36.4°C was calculated.

Effect of warming following premedication injection

Following premedication, rats in the warmed group achieved a significantly higher core temperature than unwarmed rats (warmed AUC: 6.15 ± 0.5 units and unwarmed AUC: 2.93 ± 1.0 units; 95% CI: 5.4 to −1.1, P = 0.004) (Figure 1). At the end of the 14-minute warming period, warmed rats had an increase in core temperature from baseline of 0.28°C ± 0.13°C. In contrast, unwarmed rats experienced a temperature decrease of 0.19°C ± 0.43°C over the same period and a greater variability in core temperature was observed (Figure 1). No rats crossed the hypothermia threshold during this time.

Figure 1.

Figure 1

Open in a new tab

Mean ± standard error of the mean (SEM) core body temperature following premedication with intramuscular ketamine-midazolamhydromorphone and placement in a warming box or unwarmed cage (n = 8 per treatment group). Rats in the warming box maintained a significantly higher core temperature after premedication injection (P = 0.004).

Core body temperature during general anesthesia and early recovery period

There was no significant difference between groups in the time taken to place IV catheters (warming box: 8.1 ± 1.3 min and home cage: 9.4 ± 0.9 min; 95% CI: −0.3 to 2.8, P = 0.095). During the anesthesia period, warmed rats continued to maintain a significantly higher core temperature (warmed AUC: 32.2 ± 2.2 units and unwarmed AUC: 14.5 ± 2.5; 95% CI: −24.2 to 11.0, P < 0.0001) (Figure 2). At the end of the 30 min of isoflurane anesthesia, 2/8 and 6/8 of the warmed and unwarmed rats were hypothermic, respectively.

Figure 2.

Figure 2

Open in a new tab

Mean ± SEM core body temperature of rats during 30 min of general anesthesia with isoflurane and recovery, following initial warming box or unwarmed cage treatment (n = 8 per treatment group). Rats in the warming box group maintained a significantly higher temperature throughout the anesthesia (P < 0.0001). The broken horizontal line represents the hypothermia threshold (36.4°C).

Discussion

The main findings of this study are that: i) pre-warming instituted after premedication and before general anesthesia raised core body temperature, whereas no warming resulted in a slight reduction in temperature; and ii) pre-warming followed by active warming reduced hypothermia in rats anesthetized with isoflurane.

Hypothermia during general anesthesia is well-documented (5,6,21), although there are few reports of the effect of premedication and consequent reduction in activity and body temperature in animals (1,22,23). These studies on premedication show that sedation (and concurrent reduction in activity, when measured) is associated with a decrease in body temperature. These findings broadly agree with those reported here. The magnitude of temperature reduction is difficult to compare with the results reported here, as the observation period following premedication in this study was substantially shorter (14 min) than those in the literature (60 to 75 min). Furthermore, rectal temperatures were recorded in the literature, which typically underestimate core body temperature and the relationship between the 2 may be inconsistent (7,19).

The consequences of hypothermia are well-described in human medicine. Notably, a reduction of 1°C in core temperature (i.e., a 2.7% decrease below normal) results in a multitude of adverse effects, including an increase in transfusion requirements, coagulopathy, myocardial hypoxia and arrhythmia, prolonged recovery, immunosuppression, increased susceptibility to surgical site infections, and altered drug pharmacokinetics (15,16,24,25). Hypothermia also affects patient well-being, with discomfort from shivering in recovery from anesthesia described as comparable to postoperative pain (26). The consequences of hypothermia in animals are less well-established due to the small number of reported studies. Cardiovascular adverse effects include reduction in heart rates and cardiac output (27) and a prolongation of the QT interval. Over a spectrum of core temperatures ranging from 34.2 to 42.1°C, a linear relationship was exhibited between corrected QT intervals and core temperature, with an increasing QT interval as temperature decreased (28). In humans, a prolonged QT interval was associated with increased mortality (29). In rats, the risk of hemorrhage following a femoral injury was significantly increased by hypothermia, with estimated recorded losses of nearly half the total blood volume at low temperatures (30°C), but significant bleeding also occurring at 35°C (30). Delayed recoveries have also been identified in both rats and dogs. For example, warmed rats achieved return of righting reflex approximately 4 times faster than unwarmed rats [125 s (70 to 186) versus 525 s (229 to 652)] (7). Following anesthesia, warmer dogs (rectal temperatures > 38°C) achieved sternal recumbency 2 times faster than dogs with lower temperatures (35.5 to 35.9°C) (2). Hypothermia has also been documented as a confounding factor on data quality in laboratory mice, with hypothermic animals displaying greater data variability. Consequently, results from such studies are misleading, harder to reproduce, and lead to increased animal use (31).

The results presented here highlight the greater variability in individual temperature when external warming is not provided. Contributing factors were not identified but it appears that the provision of external warming reduces the extent of individual variability. Sources of variability could include recent activity level, diurnal variation, variability in drug response, and sex, among others. Interestingly, during the period of isoflurane anesthesia, variability in the unwarmed group was closer to that of the warmed group, suggesting that the addition of external warming (heat pad) during this period contributed to the observed reduction in variability.

Despite these recognized adverse effects, the incidence of hypothermia in animals is substantial. In dogs and cats, the incidence of post-anesthetic hypothermia ranges from 84 to 97% (1,5,6). The incidence of hypothermia in rodents is not widely reported; however, the rapid decrease in core temperature observed in unwarmed animals suggests that the incidence of post-anesthetic hypothermia is similarly high (7,18,32,33).

To counteract the phenomenon of hypothermia developing rapidly after induction of general anesthesia, the concept of prewarming was investigated in humans and shown to be effective. Underlying this approach is the recognition that the redistribution of warm blood from the core to the periphery that accompanies induction of anesthesia accounts for 80% of the decrease in body temperature during the first hour of anesthesia (34,35). As shown here and in previous studies in rats and humans, pre-warming alone slows the onset of hypothermia following anesthetic induction but does not prevent it altogether (with the exception of very short anesthetics) unless accompanied by active warming during anesthesia (7,19,36–38).

In rats, pre-warming alone conferred protection against hypothermia for approximately 15 min, a period insufficient for many procedures (19). In contrast, the combination of pre-warming followed by active warming after induction of anesthesia was more effective at maintaining normothermia, although it should be noted that hypothermia could still occur during recovery (7,8,20). In these studies, as is typical in experimental settings, no premedication was provided before inducing anesthesia with a volatile agent in an induction chamber. In this current study, premedication was used to mimic an alternative management strategy, more commonly employed in clinical veterinary practice.

Limitations

The experimenter performing the study could not be blinded to the treatment groups due to the study design. This was mitigated in part by having an experimenter unfamiliar with the study perform the data analysis.

The sham surgical preparation did not include any incisions being performed; an open incision into a body cavity is likely to accelerate heat loss through an increase in exposed surface area.

This study reflects a heterogenous population (males and females, with an age span of 19 wk and body mass spanning 367 g). As a result, conclusions cannot be drawn regarding the response of subpopulations (e.g., smaller female rats) as the study was not powered to enable subpopulation analysis. Data from human studies has shown sex differences in thermoregulation (39).

In conclusion, premedication with ketamine-midazolam-hydromorphone resulted in a slight reduction in body temperature in unwarmed rats. This was prevented, and an increase in temperature observed, when warming was provided following premedication. Pre-warming followed by active warming is an effective strategy to reduce hypothermia during general anesthesia.

Acknowledgments

Funding provided by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant (424022-201) and the Fondation J.-Louis Lévesque. Author KS received support in the form of a salary from Vetronic Services, who provided the warming box.

Footnotes

The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. KS designed and built the warming box and reviewed the final draft of the manuscript for grammatical and typographical errors.

References

  • 1.Rose N, Kwong GP, Pang DS. A clinical audit cycle of postoperative hypothermia in dogs. J Small Anim Pract. 2016;57:447–452. doi: 10.1111/jsap.12547. [DOI] [PubMed] [Google Scholar]
  • 2.Pottie RG, Dart CM, Perkins NR, Hodgson DR. Effect of hypothermia on recovery from general anaesthesia in the dog. Aust Vet J. 2007;85:158–162. doi: 10.1111/j.1751-0813.2007.00128.x. [DOI] [PubMed] [Google Scholar]
  • 3.Sessler DI. Complications and treatment of mild hypothermia. Anesthesiology. 2001;95:531–543. doi: 10.1097/00000542-200108000-00040. [DOI] [PubMed] [Google Scholar]
  • 4.Sessler DI. Perioperative thermoregulation and heat balance. Lancet. 2016;387:2655–2664. doi: 10.1016/S0140-6736(15)00981-2. [DOI] [PubMed] [Google Scholar]
  • 5.Redondo JI, Suesta P, Gil L, Soler G, Serra I, Soler C. Retrospective study of the prevalence of postanaesthetic hypothermia in cats. Vet Rec. 2012;170:206. doi: 10.1136/vr.100184. [DOI] [PubMed] [Google Scholar]
  • 6.Redondo JI, Suesta P, Serra I, et al. Retrospective study of the prevalence of postanaesthetic hypothermia in dogs. Vet Rec. 2012;171:374. doi: 10.1136/vr.100476. [DOI] [PubMed] [Google Scholar]
  • 7.Schuster CJ, Pang DS. Forced-air pre-warming prevents perianaesthetic hypothermia and shortens recovery in adult rats. Lab Anim. 2018;52:142–151. doi: 10.1177/0023677217712539. [DOI] [PubMed] [Google Scholar]
  • 8.Zhang EQ, Knight CG, Pang DS. Heating pad performance and efficacy of 2 durations of warming after isoflurane anesthesia of Sprague-Dawley rats (Rattus norvegicus) J Am Assoc Lab Anim Sci. 2017;56:786–791. [PMC free article] [PubMed] [Google Scholar]
  • 9.Waterman A. Accidental hypothermia during anaesthesia in dogs and cats. Vet Rec. 1975;96:308–313. doi: 10.1136/vr.96.14.308. [DOI] [PubMed] [Google Scholar]
  • 10.Satinoff E. Neural organization and evolution of thermal regulation in mammals. Science. 1978;201:16–22. doi: 10.1126/science.351802. [DOI] [PubMed] [Google Scholar]
  • 11.Kurz A. Physiology of thermoregulation. Best Pract Res Clin Anaesthesiol. 2008;22:627–644. doi: 10.1016/j.bpa.2008.06.004. [DOI] [PubMed] [Google Scholar]
  • 12.Matsukawa T, Kurz A, Sessler DI, Bjorksten AR, Merrifield B, Cheng C. Propofol linearly reduces the vasoconstriction and shivering thresholds. Anesthesiology. 1995;82:1169–1180. doi: 10.1097/00000542-199505000-00012. [DOI] [PubMed] [Google Scholar]
  • 13.Xiong J, Kurz A, Sessler DI, et al. Isoflurane produces marked and nonlinear decreases in the vasoconstriction and shivering thresholds. Anesthesiology. 1996;85:240–245. doi: 10.1097/00000542-199608000-00003. [DOI] [PubMed] [Google Scholar]
  • 14.Matsukawa T, Sessler DI, Christensen R, Ozaki M, Schroeder M. Heat flow and distribution during epidural anesthesia. Anesthesiology. 1995;83:961–967. doi: 10.1097/00000542-199511000-00008. [DOI] [PubMed] [Google Scholar]
  • 15.Kurz A, Sessler DI, Lenhardt R. Perioperative normothermia to reduce the incidence of surgical-wound infection and shorten hospitalization. N Engl J Med. 1996;334:1209–1215. doi: 10.1056/NEJM199605093341901. [DOI] [PubMed] [Google Scholar]
  • 16.Schmied H, Kurz A, Sessler DI, Kozek S, Reiter A. Mild hypothermia increases blood loss and transfusion requirements during total hip arthroplasty. Lancet. 1996;347:289–292. doi: 10.1016/s0140-6736(96)90466-3. [DOI] [PubMed] [Google Scholar]
  • 17.Kurz A, Sessler DI, Narzt E, et al. Postoperative hemodynamic and thermoregulatory consequences of intraoperative core hypothermia. J Clin Anesth. 1995;7:359–366. doi: 10.1016/0952-8180(95)00028-g. [DOI] [PubMed] [Google Scholar]
  • 18.Caro AC, Hankenson FC, Marx JO. Comparison of thermoregulatory devices used during anesthesia of C57BL/6 mice and correlations between body temperature and physiologic parameters. J Am Assoc Lab Anim Sci. 2013;52:577–583. [PMC free article] [PubMed] [Google Scholar]
  • 19.Rufiange M, Leung VS, Simpson K, Pang DS. Pre-warming before general anesthesia with isoflurane delays the onset of hypothermia in rats. PLoS One. 2020;15:e0219722. doi: 10.1371/journal.pone.0219722. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 20.Rufiange M, Leung VS, Simpson K, Pang DS. Prewarming followed by active warming is superior to passive warming in preventing hypothermia for short procedures in adult rats (Rattus norvegicus) under isoflurane anesthesia. J Am Assoc Lab Anim Sci. 2020;59:377–383. doi: 10.30802/AALAS-JAALAS-19-000114. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 21.Hart SR, Bordes B, Hart J, Corsino D, Harmon D. Unintended perioperative hypothermia. Ochsner J. 2011;11:259–270. [PMC free article] [PubMed] [Google Scholar]
  • 22.Lessin AW, Parkes MW. The relation between sedation and body temperature in the mouse. Br J Pharmacol Chemother. 1957;12:245–250. doi: 10.1111/j.1476-5381.1957.tb00128.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23.Maney JK. Sedative and physiologic effects of low-dose intramuscular alfaxalone in dogs. Vet Anaesth Analg. 2017;44:1184–1188. doi: 10.1016/j.vaa.2016.11.013. [DOI] [PubMed] [Google Scholar]
  • 24.Sessler DI, Rubinstein EH, Moayeri A. Physiologic responses to mild perianesthetic hypothermia in humans. Anesthesiology. 1991;75:594–610. doi: 10.1097/00000542-199110000-00009. [DOI] [PubMed] [Google Scholar]
  • 25.Reynolds L, Beckmann J, Kurz A. Perioperative complications of hypothermia. Best Pract Res Clin Anaesthesiol. 2008;22:645–657. doi: 10.1016/j.bpa.2008.07.005. [DOI] [PubMed] [Google Scholar]
  • 26.De Witte J, Sessler DI. Perioperative shivering: Physiology and pharmacology. Anesthesiology. 2002;96:467–484. doi: 10.1097/00000542-200202000-00036. [DOI] [PubMed] [Google Scholar]
  • 27.Palo M, Lauri T, Timisjärvi J. Effects on dogs of surface-induced hypothermia and rewarming on the right heart function and pulmonary circulation. Eur J Appl Physiol. 2000;81:391–396. doi: 10.1007/s004210050059. [DOI] [PubMed] [Google Scholar]
  • 28.van der Linde HJ, Deuren BV, Teisman A, Towart R, Gallacher DJ. The effect of changes in core body temperature on the QT interval in beagle dogs: A previously ignored phenomenon, with a method for correction. Br J Pharmacol. 2008;154:1474–1481. doi: 10.1038/bjp.2008.265. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 29.Algra A, Tijssen JG, Roelandt JR, Pool J, Lubsen J. QTc prolongation measured by standard 12-lead electrocardiography is an independent risk factor for sudden death due to cardiac arrest. Circulation. 1991;83:1888–1894. doi: 10.1161/01.cir.83.6.1888. [DOI] [PubMed] [Google Scholar]
  • 30.Heinius G, Hahn RG, Sondén A. Hypothermia increases rebleeding during uncontrolled hemorrhage in the rat. Shock. 2011;36:60–66. doi: 10.1097/SHK.0b013e3182116143. [DOI] [PubMed] [Google Scholar]
  • 31.Marschner JA, Schäfer H, Holderied A, Anders HJ. Optimizing mouse surgery with online rectal temperature monitoring and preoperative heat supply. Effects on post-ischemic acute kidney injury. PLoS One. 2016;11:e0149489. doi: 10.1371/journal.pone.0149489. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 32.Albrecht M, Henke J, Tacke S, Markert M, Guth B. Effects of isoflurane, ketamine-xylazine and a combination of medetomidine, midazolam and fentanyl on physiological variables continuously measured by telemetry in Wistar rats. BMC Vet Res. 2014;10:198. doi: 10.1186/s12917-014-0198-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 33.Taylor DK. Study of two devices used to maintain normothermia in rats and mice during general anesthesia. J Am Assoc Lab Anim Sci. 2007;46:37–41. [PubMed] [Google Scholar]
  • 34.Torossian A. Thermal management during anaesthesia and thermoregulation standards for the prevention of inadvertent perioperative hypothermia. Best Pract Res Clin Anaesthesiol. 2008;22:659–668. doi: 10.1016/j.bpa.2008.07.006. [DOI] [PubMed] [Google Scholar]
  • 35.Sessler DI, Schroeder M, Merrifield B, Matsukawa T, Cheng C. Optimal duration and temperature of prewarming. Anesthesiology. 1995;82:674–681. doi: 10.1097/00000542-199503000-00009. [DOI] [PubMed] [Google Scholar]
  • 36.Andrzejowski J, Hoyle J, Eapen G, Turnbull D. Effect of prewarming on post-induction core temperature and the incidence of inadvertent perioperative hypothermia in patients undergoing general anaesthesia. Br J Anaesth. 2008;101:627–631. doi: 10.1093/bja/aen272. [DOI] [PubMed] [Google Scholar]
  • 37.Camus Y, Delva E, Sessler DI, Lienhart A. Pre-induction skin-surface warming minimizes intraoperative core hypothermia. J Clin Anesth. 1995;7:384–388. doi: 10.1016/0952-8180(95)00051-i. [DOI] [PubMed] [Google Scholar]
  • 38.Kim JY, Shinn H, Oh YJ, Hong YW, Kwak HJ, Kwak YL. The effect of skin surface warming during anesthesia preparation on preventing redistribution hypothermia in the early operative period of off-pump coronary artery bypass surgery. Eur J Cardiothorac Surg. 2006;29:343–347. doi: 10.1016/j.ejcts.2005.12.020. [DOI] [PubMed] [Google Scholar]
  • 39.Washington DE, Sessler DI, Moayeri A, et al. Thermoregulatory responses to hyperthermia during isoflurane anesthesia in humans. J Appl Physiol. 1993;74:82–87. doi: 10.1152/jappl.1993.74.1.82. [DOI] [PubMed] [Google Scholar]

Articles from Canadian Journal of Veterinary Research are provided here courtesy of Canadian Veterinary Medical Association

RESOURCES