Heatstroke: A Review
Jodi Thompson, DVM
Heatstroke is defined as an elevation in body temperature > 105.8°F and characterized by central nervous system dysfunction and organ derangements. Unlike a fever, the temperature set point remains normal, however the ability to dissipate heat from the body is impaired.
There are two categories of heatstroke:
Exertional
This is due to excessive exercise in hot or humid weather, or less commonly muscle activity that occurs with seizures or severe tremors.
Non-exertional
Non-exertional heatstroke is due to exposure to a heat source and is most commonly seen secondary to entrapment in a hot car. Brachycephalic conformation, laryngeal paralysis, obesity, water deprivation and excessive humidity can be contributing factors.
On presentation, the body temperature is generally >105.0°F, although it may have normalized or they may be hypothermic if cooling measures were instituted prior to arrival. Diarrhea, hematochezia, and petechiae are common. Other exam findings may include hyperemic mucous membranes, tachycardia or ventricular arrhythmia, hypotension, tremors, seizures, stupor or coma. Effects on the body are multisystemic and are attributable to direct thermal injury, alterations in cell membrane stability and cellular enzyme activity that occur above 109°F, microthrombi formation and/or hemorrhage secondary to DIC and hypoperfusion. Hypoperfusion or shock may be relative/distributive (vasodilation and venous pooling) or hypovolemic due to GI losses.
Possible Systemic Effects of Heatstroke
Treatment Options
Close monitoring is needed and should include frequent evaluation of perfusion parameters, EKG monitoring, urine output, mentation and laboratory monitoring with more frequent evaluation of glucose, electrolytes and coagulation profiles.
Prognosis varies, but is overall guarded with a reported mortality of around 50%. Negative prognostic indicators include:
- a time lag of >1.5 hours prior to presentation
- hypothermia or severe hyperthermia at > 109°F on presentation
- severe CNS signs including seizures
- hypoglycemia
- prolonged PT/PTT
- >18 nRBCS/100 WBC
- obesity
- development of DIC or AKI
Most non-survivors die or are euthanized in the first 24-48 hours, thus response to therapy in the first 24 hours can be used to help counsel owners and may be a better prognostic indicator than initial presenting signs. Pet owners should be prepared for several days or longer in the hospital with the possibility of extensive cost depending on the level of care that is needed. Dogs that recover may be predisposed to another episode due to damage to the thermoregulatory center.
Resources
- Teichmann S, Turkovic V, Dorfelt R: [Heatstroke in dogs in southern Germany. A retrospective study over a 5.5-year period]. Tierarztl Prax Ausg K Klientiere Heimtiere 2014 Vol 42 (4) pp. 213-22
- Carr M: The Pathophysiology and Treatment of Heat Stroke. International Veterinary Emergency and Critical Care Symposium 2003.
- Bruchim Y: Canine Heatstroke: Patient Management. International Veterinary Emergency and Critical Care Symposium 2016
- Bruchim Y: Canine Heatstroke: Presentation and Patient Assessment.International Veterinary Emergency and Critical Care Symposium 2016
- Hemmelgarn C, Gannon K: Heatstroke: Clinical Signs, Diagnosis, Treatment, and Prognosis. Compendium. 2013;35(7):E1-7
- Shell L, Carr A, Rothrock K: (2017, September 11). Heatstroke. Vincyclopedia of Diseases. https://www.vin.com/Members/Associate/Associate.plx?from=GetDzInfo& DiseaseId=1222&pid=607.