Equis ISSN 2398-2977

Hypothermia

Synonym(s): Exposure

Contributor(s): Janice Sojka, Han van der Kolk

Introduction

  • Hypothermia is a state in which an organism's temperature drops below normal ranges. In the horse, this is <37.5°C (99.5°F). At these low temperatures normal metabolism and bodily functions do not occur.
  • Hypothermia is also considered the clinical state of sub-normal temperature when the body is unable to generate sufficient heat to efficiently maintain functions.
  • As equids that have evolved in temperate climates, horses are extremely resistent to hypothermia. Reported cases in adult horses are limited to cases in which the animals are immersed in cold water when air temperatures are below freezing, the ambient temperature is below -34°C (-30°F), or the horse suffers from another disease.
  • Donkeys are more susceptible to hypothermia than horses.
  • Neonatal foals have minimal fat stores and a greater surface area, and hypothermia is a fairly common finding in neonatal (<2 weeks of age) foals with sepsis or other life-threatening conditions.

Pathogenesis

Etiology

  • Cooling of the core body temperature below normal levels so that normal physiologic processes do not occur.

Predisposing factors

General
  • Ambient temperatures below -34°C with no shelter.
  • Immersion in cold water.
  • Sepsis or severe systemic illness.
  • Limited caloric intake.
  • Hypothyroidism.

Specific

  • There are 5 distinct mechanisms involved with cooling of a warm blooded animal:
    • Conduction: direct transfer of heat by contact with a cooler object - conduction of heat to the cooler object.
    • Convection: cool air moving across the surface of the body, heat transferred to the cool air, warming it and cooling the body.
    • Radiation: heat radiated outward from the warm body to the cooler environment.
    • Evaporation: the loss of heat through the process of removing water from the surface of the body through vaporization.
    • Respiration: inspired air raised to body temperature and then exhaled.
  • Each of these causes of heat loss can play a large or small role in the development of hypothermia.

Pathophysiology

  • As horse loses ability to maintain normal body heat, the enzymatic processes of the body cease to function well. This leads to generalized metabolic disturbances. 
  • Foals have very limited energy reserves and thus cannot generate body heat if they lack a calorie source.

Timecourse

  • Variable.
  • Published reports of horses that were hypothermic due to immersion in cold water had been in the cold environment for several hours.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Stephen J O, Baptiste K E & Townsend H G G (2000) Clinical and pathologic findings in donkey with hypothermia: 10 cases (1988-1998)JAVMA 216, 725-729 PubMed.

Other sources of information

  • Webb A I (1990) Neonatal Resuscitation. In: Equine Clinical Neonatology. Eds: Koterba A M, Drummond W H & Kosch P C. Lea & Febiger, USA. pp 136-149.


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