Felis ISSN 2398-2950

Hyperthermia

Synonym(s): afebrile hyperthermia, pathological hyperthermia, malignant hyperthermia

Contributor(s): Martha Cannon, Poppy Gant, Stefano Cortellini

Introduction

  • Definition:
    • Hyperthermia: an elevation in core body temperature above accepted normal ranges secondary to an imbalance between heat production and heat loss.
    • Distinguish from true fever (or pyrexia) - the body’s normal response to endogenous pyrogens (produced during infection, inflammation or injury). It is associated with an increase in the ‘set point’ in the thermoregulatory center in the hypothalamus.
  • Pathophysiology: heat production exceeds heat loss.
  • Signs: variable based on severity and duration. Cats are less likely to suffer from heat stroke or exertional hyperthermia and as such may be more likely to display clinical signs associated with an underlying trigger.
  • Diagnosis: based on history and physical examination. Baseline blood tests may determine development of secondary organ injury or underlying disease process.
  • Treatment: focuses on active cooling or management of underlying disease process.
  • Prevention: minimize environmental risk factors, exposure to triggers, control underlying disease.
  • Prognosis: dependent on severity and duration and underlying disease.

Pathogenesis

Predisposing factors

Patient related

  • Heat stroke Heat stroke: not as commonly reported in cats compared to dogs although same pathophysiology and treatment likely applies:
  • Exertional hyperthermia is more likely secondary to underlying disease (tetany or seizure disorders Seizures) or intoxications (eg amphetamines) than ‘exercise’ induced.
  • Older cats are frequently affected by hyperthyroidism Hyperthyroidism. Sudden cessation of medication or radioactive iodine treatment can predispose to thyroid storm.
  • Certain amphetamine medication used to treat attention deficit hyperactivity disorders is palatable to cats.

Environment related

  • Confinement in a hot, unventilated environment, eg trapped in a shed/garage, confinement in a closed car.
  • High humidity
  • Inadequate ventilation.
  • Close confinement.

Pathophysiology

  • Information from peripheral and central thermoreceptors is normally conveyed to the hypothalamus in order to tightly regulate body temperature.
  • If required, the hypothalamus can stimulate heat loss mechanisms, eg panting, vasodilation, behavioral and postural changes to aid heat dissipation.
  • Hyperthermia results when physiological, pathological or pharmacological changes cause heat production to exceed heat loss.
  • Temperatures above 41.6°C (106.88°F) can start to cause cellular damage secondary to relative hypoxemia Hypoxemia.
  • Exertional heat stroke and malignant hyperthermia can also cause rhabdomyolysis with myoglobinemia.
  • In severe cases a lack of cellular oxygen can quickly lead to multiple organ dysfunction Multiple organ dysfunction syndrome (MODS) and failure:
    • Cardiac (leading to arrhythmias).
    • Acute kidney injury Kidney: acute renal failure
    • Hepatic injury (risk of hypoglycemia and development of hyperbilirubinemia).
    • Gastrointestinal tract injury (endotoxin absorption/hemorrhage).
    • Disseminated intravascular coagulation Disseminated intravascular coagulation (leading to thrombosis/bleeding).
    • Cerebral edema (confusion, delerium, obtundation, seizures, coma).

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.
  • Thomson S M, Burton C A, Armitage-Chan E A (2014) Intra-operative hyperthermia in a cat with a fatal outcome. Vet Anesth Analg 41(3), 290-296 PubMed.
  • Stern L & Schell M (2012) Management of attention deficit disorders and attention-deficit/hyperactivity disorder drug intoxication in dogs and cats. Vet Clin North Am Small Anim Pract 42(2), 279-287 PubMed.
  • Ward C R (2007) Feline thyroid storm. Vet Clin North Am Small Anim Pract 37(4), 754-754 PubMed.

Other sources of information

  • Miller J (2015) Hyperthermia and Fever. In: Small Animal Critical Care Medicine. 2nd edn. Silverstein D & Hopper K (eds) Elsevier. Chapter 10.
  • Drobatz K (2015) Heat Stroke. In: Small Animal Critical Care Medicine. 2nd edn. Silverstein D & Hopper K (eds) Elsevier. Chapter 167.
  • Gwaltney-Brant S M (2013) Miscellaneous indoor toxicants. In: Small Animal Toxicology. 3rd edn. Petersen M E, Talcott P A (eds). St Louis, MO: Saunders. pp 291-308. 


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