Effect of a heat and moisture exchanger on heat loss in isoflurane-anesthetized dogs undergoing single-limb orthopedic procedures

Erik H. Hofmeister Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

Search for other papers by Erik H. Hofmeister in
Current site
Google Scholar
PubMed
Close
 DVM, MA, DACVA
,
Benjamin M. Brainard Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

Search for other papers by Benjamin M. Brainard in
Current site
Google Scholar
PubMed
Close
 VMD, DACVA, DACVECC
,
Christina Braun Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

Search for other papers by Christina Braun in
Current site
Google Scholar
PubMed
Close
 Dr med vet, DACVA
, and
Juliana P. Figueiredo School of Veterinary Medicine, St George's University, St George's, Grenada, West Indies.

Search for other papers by Juliana P. Figueiredo in
Current site
Google Scholar
PubMed
Close
 Med Vet, MS, DACVA

Abstract

Objective—To determine whether a heat and moisture exchange device (HME) prevents a decrease in body temperature in isoflurane-anesthetized dogs undergoing orthopedic procedures.

Design—Blinded randomized controlled clinical trial.

Animals—60 privately owned dogs weighing at least 15 kg (33 lb).

Procedures—Dogs were randomly assigned to 1 of 3 treatment groups (n = 20/group): HME placed immediately after anesthetic induction with isoflurane, after transfer to the operating room, or not at all. The device consisted of a hygroscopic filter placed between the endotracheal tube and the Y piece of the anesthesia circuit. Each dog was positioned on a circulating warm water blanket and had a forced-air warming blanket placed over its body. Body temperature was monitored after transfer to the operating room with a probe placed in the thoracic aspect of the esophagus.

Results—Study groups did not differ significantly with respect to body weight, body condition score, reproductive status, breed, surgical procedure, preoperative sedative and opioid administration, anesthetic induction drug, local nerve block technique, or operating room assignment. There were no significant differences among groups in esophageal temperature variables, interval between anesthetic induction and surgery, surgery duration, anesthesia duration, or oxygen flow rate. However, the relationship between temperature delta and body weight was significant and relevant (R2 = 0.23), as was the association between temperature nadir and body weight (R2= 0.10). As body weight increased, the temperature delta decreased and temperature nadir increased. No other significant relationships were identified.

Conclusions and Clinical Relevance—Inclusion of an HME in healthy dogs undergoing anesthesia for an elective orthopedic surgery did not facilitate maintenance of body temperature throughout the procedure.

Abstract

Objective—To determine whether a heat and moisture exchange device (HME) prevents a decrease in body temperature in isoflurane-anesthetized dogs undergoing orthopedic procedures.

Design—Blinded randomized controlled clinical trial.

Animals—60 privately owned dogs weighing at least 15 kg (33 lb).

Procedures—Dogs were randomly assigned to 1 of 3 treatment groups (n = 20/group): HME placed immediately after anesthetic induction with isoflurane, after transfer to the operating room, or not at all. The device consisted of a hygroscopic filter placed between the endotracheal tube and the Y piece of the anesthesia circuit. Each dog was positioned on a circulating warm water blanket and had a forced-air warming blanket placed over its body. Body temperature was monitored after transfer to the operating room with a probe placed in the thoracic aspect of the esophagus.

Results—Study groups did not differ significantly with respect to body weight, body condition score, reproductive status, breed, surgical procedure, preoperative sedative and opioid administration, anesthetic induction drug, local nerve block technique, or operating room assignment. There were no significant differences among groups in esophageal temperature variables, interval between anesthetic induction and surgery, surgery duration, anesthesia duration, or oxygen flow rate. However, the relationship between temperature delta and body weight was significant and relevant (R2 = 0.23), as was the association between temperature nadir and body weight (R2= 0.10). As body weight increased, the temperature delta decreased and temperature nadir increased. No other significant relationships were identified.

Conclusions and Clinical Relevance—Inclusion of an HME in healthy dogs undergoing anesthesia for an elective orthopedic surgery did not facilitate maintenance of body temperature throughout the procedure.

Hypothermia, defined as a core body temperature < 35°C (95°F), commonly develops in anesthetized dogs.1 It results from a combination of effects from volatile inhaled anesthetic agents, which cause vasodilation (and subsequent increase in cutaneous perfusion) and loss of central temperature regulation. Delivery to the bronchial tree of cool, dry gas from oxygen supplies may compound heat loss.2 In addition, surgical preparation (including clipping of hair and application of surgical scrub solution) and exposure of internal body cavities contribute to heat loss in dogs undergoing surgery.3

When heat loss is sufficient to result in hypothermia, numerous adverse effects can occur. These include prolonged anesthetic recovery, a decrease in drug metabolism or immune function, an increase in the physiologic stress response, and cardiovascular dysfunction (bradycardia, ventricular fibrillation, and hypotension).4,5 The thermogenic response to postoperative hypothermia (shivering) may also be detrimental because it increases total body oxygen demand and may lead to postoperative discomfort and metabolic acidosis.6 In humans, postoperative hypothermia of < 36.1°C (97°F) is associated with a significant increase in mortality rate.7 Hence, maintenance of core temperature in anesthetized dogs is highly desirable.

The beneficial effects of core temperature maintenance can be achieved by wrapping limbs in warm water blankets, positioning dogs on an electrical heating blanket, and using convective warming, radiant heat, and active heater and humidifier devices.8–10 Active heater and humidifier devices make use of a reservoir of heated water, which adds warm vapor to the inspiratory gases to achieve humidification and increase the temperature of inspired gases. Such devices are fairly expensive and require maintenance.8 Passive HMEs make use of the patient's expired gas to saturate and warm a small unit placed between the endotracheal tube and the Y piece of the anesthesia circuit.11 Unlike the other devices, HMEs are easy to use and relatively inexpensive.

The primary purpose of the study reported here was to determine whether use of an HME would prevent a decrease in body temperature (rectal and esophageal) in dogs anesthetized with isoflurane undergoing orthopedic procedures. A second purpose was to determine whether the timing of HME placement within the anesthesia circuit would affect heat loss. The hypothesis was that an HME helps maintain body temperature when placed immediately after anesthetic induction but does not help to warm a dog when placed into the circuit after an initial period of heat loss.

Materials and Methods

Animals—Dogs brought to the anesthesia service at the University of Georgia to undergo elective orthopedic surgery of only 1 limb were evaluated for inclusion in the study. A power analysis was performed by use of data from the records of 11 randomly selected dogs that underwent elective 1-limb orthopedic surgery in the month preceding study initiation. To detect a 1°C (2°F) difference in nadir temperature for a value of α = 0.05 and a β = 0.1, at least 14 dogs would be required for each group. To allow for increased variability and to test other temperature variables, 20 dogs were sought for each group.

Criteria for inclusion were as follows: American Society of Anesthesiologists physical status score of I or II, age of 8 months to 10 years, body weight ≥ 15 kg (33 lb), and otherwise healthy on the basis of physical examination and various other findings (PCV, plasma total solids concentration, BUN concentration, and blood glucose concentration). Body condition score was assigned in accordance with a standardized system.12 Dog breed, reproductive status, anesthetic protocol, surgery room assignment (to control for the potential of slight differences in room temperature or air flow), and type of surgical procedure were recorded. The study protocol was approved by the Clinical Research committee of the University of Georgia Veterinary Teaching Hospital.

Study protocol—Dogs were randomly assigned to 1 of 3 treatment groups (n = 20/group): HME placed by use of a hygroscopic filtera immediately after induction (induction group), after transfer to the OR (OR group), or not at all (control group). For control dogs, the filter was removed from the HME and the device shell attached to the circuit. For OR group dogs, a filter-removed HME was applied after induction and exchanged with a filter-intact HME upon transfer to the OR. For all groups, the HME was covered in opaque white tape to ensure blinding of the veterinary students and technicians who managed the patients. To minimize bias, these people were not informed of the study methodology. Investigators aware of treatment group assignment did not directly participate in patient management. Investigators unaware of treatment group assignment were permitted to be directly involved in patient management.

The premedication and anesthetic induction protocol was not standardized and was determined by senior veterinary students assigned to the anesthesia service working with the supervising faculty. Anesthesia in all dogs was maintained with isoflurane in oxygen delivered to effect, as determined by the senior student supervising the case. A rebreathing anesthesia circuit was used in a semiclosed fashion. Locoregional anesthesia was administered when indicated (eg, epidural for hind limb procedure and brachial plexus block for distal fore-limb procedure). Each dog was positioned on a circulating warm water blanketb and had a forced-air warming blanketc placed over its body at surgery start time. The blanket was set to the highest setting (43°C [109°F]). For all procedures, routine anesthetic measurements (heart rate, blood pressure, respiratory rate, flowmeter and vaporizer settings, and end-tidal carbon dioxide and end-tidal isoflurane measurements) were recorded every 5 minutes. Any physiologic disturbances (bradyarrythmias or tachyarrhythmias and hypertension or hypotension) were recorded and were treated at the discretion of the supervising anesthetist. Amount and types of any drugs administered during surgery were recorded.

Body temperature recording—A rectally positioned, noncalibrated, handheld thermometer was used to measure body temperature within 10 minutes after anesthetic induction (baseline temperature) and again after extubation. Body temperature monitoring after transfer to the OR was performed by use of a probe placed in the thoracic aspect of the esophagus.d Probe placement was confirmed by 1 investigator (EHH) on the basis of ease of placement, external detection of the probe's passage into the cervical region, and distance of passage. Prior to the start of the study and again at the end, the thermometers used to measure esophageal temperature were calibrated against each other by means of a series of warm water measurements obtained at 12 points between 31° and 40°C (88° and 104°F).

Esophageal temperatures were recorded continuously throughout surgery. The temperature delta was calculated as the difference between surgery end temperature and surgery start temperature. The temperature nadir was the lowest recorded temperature recorded between induction of anesthesia and end of surgery. The initial decrease was the change in esophageal temperature from surgery start to the nadir. The temperature recovery was the change in esophageal temperature from the nadir to surgery end. The interval from induction to surgery start, duration of surgery, and duration of anesthesia (ie, anesthesia induction to discontinuing inhalant anesthetic delivery) were all calculated. The mean fresh oxygen flow used to administer isoflurane was calculated by calculating the mean of blocks of time in 5-minute segments from the start of anesthesia to the end of surgery. If esophageal temperature exceeded 39°C (102°F) or was below 33°C (91°F), then the dog was removed from the study and managed according to the supervising anesthesiologist's protocol.

Statistical analysis—Normality of data distribution was evaluated with the Kolmogorov-Smirnov test. Differences among the 3 study groups with respect to categorical data (ie, reproductive status, surgical procedure, and anesthetic protocol) were analyzed by use of a χ2 test. Specific sedative and specific opioid types used in the premedication were analyzed separately. Normally distributed data were analyzed by use of a 1-way ANOVA with the Tukey test for post hoc comparisons. Nonnormally distributed data were analyzed by use of a Kruskal-Wallis test with the Dunn multiple comparison test for post hoc comparisons. Comparisons between the temperature nadir and temperature delta were made for anesthesia duration, mean oxygen flow, interval from induction to surgery start, BCS, body weight, and age by use of linear regression. Significance was set at a value of P < 0.05.

Results

Animals—No dog developed a body temperature < 33°C (91°F) or > 39°C (102°F). Patient characteristics for the 3 groups were summarized (Table 1). Dogs in the induction group were significantly older than were patients in the other 2 groups. No significant differences existed for weight, BCS, sex, breed, surgical procedure, premedication sedative, premedication opioid, induction drug, local nerve block technique, or OR assignment. Preservative-free morphine (0.1 mg/kg [0.045 mg/lb]) and bupivacaine (0.5 mg/kg [0.23 mg/lb]) were administered epidurally in 85% (17/20), 85% (17/20), and 95% (19/20) of dogs in the induction, OR, and control groups, respectively.

Table 1—

Characteristics and treatments of privately owned dogs assigned to receive a passive HME at anesthetic induction (induction group; n = 20), after transfer to the OR (OR group; 20), or not at all (control group; 20) prior to undergoing orthopedic surgery involving 1 limb.

VariableInductionORControl
Age (mo)72 ± 32*51 ± 2548 ± 17
Body weight (kg)35 ± 7.433 ± 8.932 ± 7.7
BCS (1–9)6.2 ± 1.65.3 ± 1.16.0 ± 1.1
Reproductive status
   Sexually intact male010
   Neutered male877
   Sexually intact female011
   Spayed female121112
Surgical procedure
   TPLO or TTA161413
   THR326
   Lateral suture111
   Forelimb arthroscopy010
   MPL correction020
Locoregional anesthetic technique
   Epidural with morphine and bupivacaine171719
   Epidural with medetomidine, morphine, and bupivacaine001
   Epidural with morphine alone120
   Paravertebral block with bupivacaine010
   None200
Sedative
   Acepromazine131211
   Midazolam636
   Medetomidine or dexmedetomidine153
Opioid
   Hydromorphone131115
   Morphine795
Anesthesia induction agent
   Thiopental787
   Propofol443
   Ketamine and diazepam9810

Data for age, body weight, and BCS are reported as mean ± SD. All other data represent the number of dogs with the indicated attribute.

Value differs significantly (P < 0.05) from control value.

MPL = Medial patellar luxation. THR = Total hip joint replacement. TPLO = Tibial plateau leveling osteotomy. TTA = Tibial tuberosity advancement.

No significant differences were detected among groups with respect to baseline body temperature, surgery start body temperature, change in body temperature from baseline to surgery start, surgery end body temperature, temperature delta, temperature nadir, initial body temperature decrease, interval to body temperature recovery, interval from anesthetic induction to surgery, surgery duration, anesthesia duration, or oxygen flow rate (Table 2). There was a significant and relevant relationship between temperature delta and body weight (P < 0.001; R2 = 0.23) as well as between temperature nadir and body weight (P = 0.013; R2= 0.10). As body weight increased, the temperature delta decreased and temperature nadir increased. No other significant relationships were identified.

Table 2—

Mean ± SD values for intraoperative esophageal temperature (°C) and anesthesia-related variables in privately owned dogs assigned to receive a passive HME at anesthetic induction (induction group; n = 20), after transfer to the OR (OR group; 20), or not at all (control group; 20) prior to undergoing orthopedic surgery involving 1 limb.

VariableInductionORControl
Anesthesia starttemperature37.6 ± 0.7637.2 ± 0.6037.5 ± 0.76
Surgery starttemperature36.2 ± 0.9335.9 ± 1.135.9 ± 0.75
Surgery end temperature36.4 ± 1.136.3 ± 0.9336.2 ± 0.77
Temperature delta0.20 ± 0.430.42 ± 0.730.28 ± 0.47
Temperature nadir36.1 ± 0.9835.7 ± 1.035.7 ± 0.80
Initial temperature decrease−0.11 ± 0.16−0.14 ± 0.14−0.20 ± 0.23
Temperature recovery*0.32 ± 0.350.56 ± 0.670.48 ± 0.42
Interval from anesthetic induction to surgery (min)86 ± 1793 ± 2295 ± 20
Surgery duration (min)111 ± 22111 ± 40114 ± 39
Anesthesia duration (min)238 ± 35243 ± 49248 ± 51
Oxygen flow rate (L/min)1.3 ± 0.31.3 ± 0.31.3 ± 0.3

The temperature recovery was the change in esophageal temperature from the nadir to surgery end. Values did not differ significantly (P < 0.05) among groups for any variable.

Discussion

Results of the present study indicated that inclusion of an HME from the start of anesthesia or placement of one in the anesthesia circuit after induction did not affect the loss in body temperature (as measured via esophageal probe) that typically accompanies general anesthesia in healthy medium to large dogs undergoing surgery for elective orthopedic procedures. Larger dogs in the study had a higher temperature nadir and lower temperature delta than did smaller dogs, probably because of a lower ratio of surface area to body weight in larger dogs.13 It was expected that dogs in which the HME was placed in the anesthesia circuit at induction would sustain body temperature better than would dogs in which no HME was placed or in which the HME was placed after transfer to the OR. Because all 3 groups of dogs had an equal decrease and then recovery in esophageal temperature, it can be inferred that timing of HME application did not have any effect on body temperature.

All dogs had a marked decrease in body temperature from the start of anesthesia (rectal measurement) to the start of surgery (esophageal measurement), regardless of treatment group assignment. It is likely that the effects from convective cooling (cool air blowing over the patient) and radiative cooling (loss of infrared radiation to the atmosphere) in the preparation area (typical room temperature, 20°C [68°F]) were sufficiently profound that any small effect from the HME was overwhelmed. In this setting, inclusion of an HME did not alter the initial decrease in temperature, nor did inclusion of an HME improve temperature at the start of surgery. The increase in esophageal temperature from the nadir to the end of surgery was attributable to the application of forced-air warming at the start of surgery.14

The HME likely did not yield any important effect on the study dogs because of its mechanism. Evaporation is responsible for < 10% of heat loss under usual conditions, and it is this evaporative loss that may be influenced by an HME.15 Compared with the large amounts of heat lost through convection and radiation,16 it is unlikely that making a slight change to the evaporative heat loss would result in any important difference in core body temperature.

The study groups were similar in the interval from anesthetic induction to the start of surgery and the surgery start body temperature, suggesting that they were equivalent with respect to their exposure to the preparation area and convective cooling. Surgery duration and oxygen flow rate were not different among groups, indicating that the duration of exposure to forced-air warming or differences in inspired gas flows did not influence the results.

Several points must be considered in evaluating the results reported here. Rectal temperatures were measured at the start of anesthesia with a heterogeneous group of thermometers that were not calibrated to a standard. This may have led to greater variability in the data and inaccuracies when comparing dogs. The coefficient of variation for the baseline temperatures was approximately 1.1%, compared with approximately 1.4% for the nadir temperatures measured with an esophageal probe. This indicates that the variability in data was actually not greater with the rectal thermometers than with the esophageal thermometers. Esophageal thermometers were not used before transport to the OR because they were unavailable for all dogs. We chose to report rectal temperatures only to show equivalency and not to compare them with esophageal temperatures because of the possibility of measurement bias, which would prevent us from drawing causal inferences about the data.

Esophageal temperature is well correlated with, but not identical to, core body temperature as determined by use of a pulmonary artery catheter.17 Therefore, it is possible that the core body temperatures were different from those reported here. However, given that clinical decisions are made on the basis of esophageal temperature in our clinic, we believe that the findings are appropriate for application to clinical practice.

The standard operating procedure at our clinic is for the ORs to have a set temperature of 17°C [62.6°F]. The individual OR temperatures were not recorded; however, all treatment groups had representatives in all of the ORs, and the proportion assigned to each room was not significantly different. In addition, because a forced-air warming blanket covered each dog, we believe the possible variability associated with OR temperature was not important. A warmer OR may also be useful for maintenance of patient temperature during anesthesia.

Various anesthesia protocols were used for the dogs in the present study, and it is possible that this influenced the results. For example, acepromazine maleate administration causes vasodilation, which may increase cutaneous circulation and therefore heat transfer from the body core to the periphery.18 There was no significant difference among groups in the induction agent or pre- operative sedative or opioid used. The power analysis to determine an adequate sample size was based on a similarly heterogeneous group with respect to anesthesia. We believe that this is a strength of the study because the results can be applied to dogs undergoing similarly heterogeneous anesthetic protocols. A post hoc power analysis revealed that as small as a 2°C (3.6°F) difference in body temperature among groups would have been detected with a power of 90%. Therefore, the likelihood of a type II error was small and we are confident that in the surgical scenarios described here, the use of an HME does not have an effect on maintaining body temperature in dogs.

ABBREVIATIONS

BCS

Body condition score

HME

Heat and moisture exchanger

OR

Operating room

a.

Humid-Vent, Teleflex Medical, Hith Witcombe, Buckinghamshire, England.

b.

T-Pump, model TP-500, Gaymar Industries Inc, Orchard Park, NY.

c.

BAIR Hugger, model 505, Augustine Medical Inc, Eden Prairie, Minn.

d.

Spacelabs, model 90602A, Spacelabs Inc, Redmond, Wash.

References

  • 1.

    Raffe MR, Wright M, McGrath CJ, et al. Body temperature changes during general anesthesia in the dog and cat. Vet Anesth 1980; 7:915.

  • 2.

    Solway J. Airway heat and water fluxes and the tracheobronchial circulation. Eur Respir J Suppl 1990; 12:608s617s.

  • 3.

    Matsukawa T, Sessler DI, Sessler A, et al. Heat flow and distribution during induction of general anesthesia. Anesthesiology 1995; 82:662673.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4.

    Pottie RG, Dart CM, Perkins NR, et al. Effect of hypothermia on recovery from general anaesthesia in the dog. Aust Vet J 2007; 85:158162.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5.

    Putzu M, Casati A, Berti M, et al. Clinical complications, monitoring and management of perioperative mild hypothermia: anesthesiological failures. Acta Biomed 2007; 78:163169.

    • Search Google Scholar
    • Export Citation
  • 6.

    Kurz A, Sessler DI, Narzt E, et al. Postoperative hemodynamic and thermoregulatory consequences of intraoperative core hypothermia. J Clin Anesth 1995; 7:359366.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7.

    Slotman GJ, Jed EH, Burchard KW. Adverse effects of hypothermia in postoperative patients. Am J Surg 1985; 149:495501.

  • 8.

    Raffe MR, Martin FB. Effect of inspired air heat and humidification on anesthetic-induced hypothermia in dogs. Am J Vet Res 1983; 44:455458.

    • Search Google Scholar
    • Export Citation
  • 9.

    Tan C, Govendir M, Zaki S, et al. Evaluation of four warming procedures to minimise heat loss induced by anaesthesia and surgery in dogs. Aust Vet J 2004; 82:6568.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10.

    Cabell LW, Perkowski SZ, Gregor T, et al. The effects of active peripheral skin warming on perioperative hypothermia in dogs. Vet Surg 1997; 26:7985.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11.

    Dorsch JA, Dorsch SE. Understanding anesthesia equipment. 4th ed. Philadelphia: Lippincott Williams & Wilkins, 1999;291292.

  • 12.

    Lund EM, Armstrong PJ, Kirk CA, et al. Health status and population characteristics of dogs and cats examined at private veterinary practices in the United States. J Am Vet Med Assoc 1999; 214:13361341.

    • Search Google Scholar
    • Export Citation
  • 13.

    Szmuk P, Rabb MF, Baumgartner JE, et al. Body morphology and the speed of cutaneous rewarming. Anesthesiology 2001; 95:1821.

  • 14.

    Borms SF, Engelen SL, Himpe DG, et al. Bair hugger forced-air warming maintains normothermia more effectively than thermo-lite insulation. J Clin Anesth 1994; 6:303307.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15.

    Roberge RJ, Kim JH, Coca A. Protective facemask impact on human thermoregulation: an overview [published online ahead of print Sep 13, 2011]. Ann Occup Hyg doi:10.1093/annhyg/mer069.

    • Search Google Scholar
    • Export Citation
  • 16.

    Shuran M, Nelson RA. Quantitation of energy expenditure by infrared thermography. Am J Clin Nutr 1991; 53:13611367.

  • 17.

    Hayes JK, Collette DJ, Peters JL, et al. Monitoring body-core temperature from the trachea: comparison between pulmonary artery, tympanic, esophageal, and rectal temperatures. J Clin Monit 1996; 12:261269.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 18.

    Popovic NA, Mullane JF, Yhap EO. Effects of acetylpromazine maleate on certain cardiorespiratory responses in dogs. Am J Vet Res 1972; 33:18191824.

    • Search Google Scholar
    • Export Citation
  • 1.

    Raffe MR, Wright M, McGrath CJ, et al. Body temperature changes during general anesthesia in the dog and cat. Vet Anesth 1980; 7:915.

  • 2.

    Solway J. Airway heat and water fluxes and the tracheobronchial circulation. Eur Respir J Suppl 1990; 12:608s617s.

  • 3.

    Matsukawa T, Sessler DI, Sessler A, et al. Heat flow and distribution during induction of general anesthesia. Anesthesiology 1995; 82:662673.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4.

    Pottie RG, Dart CM, Perkins NR, et al. Effect of hypothermia on recovery from general anaesthesia in the dog. Aust Vet J 2007; 85:158162.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5.

    Putzu M, Casati A, Berti M, et al. Clinical complications, monitoring and management of perioperative mild hypothermia: anesthesiological failures. Acta Biomed 2007; 78:163169.

    • Search Google Scholar
    • Export Citation
  • 6.

    Kurz A, Sessler DI, Narzt E, et al. Postoperative hemodynamic and thermoregulatory consequences of intraoperative core hypothermia. J Clin Anesth 1995; 7:359366.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7.

    Slotman GJ, Jed EH, Burchard KW. Adverse effects of hypothermia in postoperative patients. Am J Surg 1985; 149:495501.

  • 8.

    Raffe MR, Martin FB. Effect of inspired air heat and humidification on anesthetic-induced hypothermia in dogs. Am J Vet Res 1983; 44:455458.

    • Search Google Scholar
    • Export Citation
  • 9.

    Tan C, Govendir M, Zaki S, et al. Evaluation of four warming procedures to minimise heat loss induced by anaesthesia and surgery in dogs. Aust Vet J 2004; 82:6568.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10.

    Cabell LW, Perkowski SZ, Gregor T, et al. The effects of active peripheral skin warming on perioperative hypothermia in dogs. Vet Surg 1997; 26:7985.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11.

    Dorsch JA, Dorsch SE. Understanding anesthesia equipment. 4th ed. Philadelphia: Lippincott Williams & Wilkins, 1999;291292.

  • 12.

    Lund EM, Armstrong PJ, Kirk CA, et al. Health status and population characteristics of dogs and cats examined at private veterinary practices in the United States. J Am Vet Med Assoc 1999; 214:13361341.

    • Search Google Scholar
    • Export Citation
  • 13.

    Szmuk P, Rabb MF, Baumgartner JE, et al. Body morphology and the speed of cutaneous rewarming. Anesthesiology 2001; 95:1821.

  • 14.

    Borms SF, Engelen SL, Himpe DG, et al. Bair hugger forced-air warming maintains normothermia more effectively than thermo-lite insulation. J Clin Anesth 1994; 6:303307.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15.

    Roberge RJ, Kim JH, Coca A. Protective facemask impact on human thermoregulation: an overview [published online ahead of print Sep 13, 2011]. Ann Occup Hyg doi:10.1093/annhyg/mer069.

    • Search Google Scholar
    • Export Citation
  • 16.

    Shuran M, Nelson RA. Quantitation of energy expenditure by infrared thermography. Am J Clin Nutr 1991; 53:13611367.

  • 17.

    Hayes JK, Collette DJ, Peters JL, et al. Monitoring body-core temperature from the trachea: comparison between pulmonary artery, tympanic, esophageal, and rectal temperatures. J Clin Monit 1996; 12:261269.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 18.

    Popovic NA, Mullane JF, Yhap EO. Effects of acetylpromazine maleate on certain cardiorespiratory responses in dogs. Am J Vet Res 1972; 33:18191824.

    • Search Google Scholar
    • Export Citation

Advertisement