Canis ISSN: 2398-2942

Anesthesia: temperature regulation

Contributor(s): John Dodam, Sheilah Robertson, Polly Taylor, Claire Waters

Hypothermia

  • Particular problem in small dogs due to their small body size and consequent large body surface area:volume ratio. Additional problems in puppies and geriatric animals due to poor thermoregulatory ability.
  • Once a fall in body temperature Hypothermia has occurred it is very difficult to increase it until the animal has recovered from anesthesia. Therefore it is important to monitor temperature throughout anesthesia and recovery to initiate preventive measures as soon as a problem is noted.
  • Serious effects when core temperature below 30-35°C.

Signs

  • Lowered measured body temperature.
  • Progressive reduction in anesthetic requirement to maintain the same level of anesthesia.
  • Respiratory function depression.
  • Bradycardia Heart: dysrhythmia.
  • Prolonged recovery from anesthesia.
  • Excessive shivering in recovery.
  • Increased morbidity and infection rates (latter reported in man).

Causes

  • Cold environment, loss of heat by conduction, convection and radiation of heat from the animal.
    • Increased surface temperature losses: clipping, surgical preparation, cold surgery table/environment, anesthetic induced cutaneous vasodilation.
  • Evaporative loss of heat from:
    • Respiratory system.
    • Surgical site during preparation.
    • Surgical site during operative procedures especially where these involve opening into body cavities.
  • Use of cold intravenous infusion fluids or cold lavage fluids.
  • Thermoregulatory mechanisms of the animal reduced by anesthesia.

Prevention

  • Maintain a reasonable ambient temperature with minimum of 25-27°C.
  • Use insulating material between the animal and the surfaces on which it is placed, eg foam pads, or use heated surfaces, eg circulating warm water pads at 38°C.
  • Wrap the areas of the animal to which access is not required in bubble-wrap, aluminium survival blanket material.
  • Can use hot air circulators and blankets (eg Bair Hugger).
  • Place warm packs around the animal; temperature must be controlled to prevent burning the patient.
  • Areas clipped for surgery should not be over large.
  • Preparation of clipped areas should not involve 'over-wetting' other areas of the animal.
  • Surgical drapes should be kept as dry as possible and should be changed if saturated.
  • Warm fluids for infusion and lavage to 38°C. Take steps to maintain the temperature in the giving set of fluids for infusion.
  • Use small proprietary heat exchangers which also retain moisture in the breathing circuit, eg 'Thermovent' Portex. These add only a very small amount to circuit dead-space.
  • Keep anesthetic time to a minimum and avoid the use of drugs which produce prolonged recoveries.
  • Monitor core temperature intra-operatively: thoracic esophageal better than rectal.
  • Continue monitoring and preventative measures into recovery.

Treatment

  • May be impossible to raise the body temperature significantly once hypothermia has developed until the animal recovers from the anesthetic.
  • Reduce the amount of anesthetic being administered to a suitable level as hypothermia potentiates their effects, and terminate anesthesia as soon as possible.
  • Wrap the animal in warm insulating material and apply direct warmth ideally by blowing warm air from a hair dryer or fan heater into the wrapping.

    Care not to cause burns.
  • The use of heat lamps, heated pads and packs if a source of warm air is not available.

Hyperthermia

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Further Reading

Publications

Refereed papers
  • Recent references fromPubMed.

Other sources of information

  • Hall L W & Taylor P M (1994) EdsAnesthesia of the Cat. London: Bailliere Tindall. pp249-266, 270-273, 274-309. ISBN 0 7020 1665 9
  • Bedford P G C (1991)Small Animal Anesthesia, The Increased Risk Patient.London: Bailliere Tindall. pp92-132. ISBN 0 7020 1501 6.
  • Richards D L S (1989)Anesthetic accidents and emergencies.In: Manual of Anesthesia for Small Animal Practice. Ed: A D R Hilbery. Cheltenham: British Small Animal Veterinary Association. pp95-99. ISBN 0 905214 09 9.
  • Hall L W (1982)Relaxant drugs in small animal anesthesia.In: Proceedings of the Association of Veterinary Anesthetists of Great Britain and IrelandSupplement to 10, pp144-155.


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