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Heat stroke



  • Cause: inadequate heat dissipation after exposure to excessively increased ambient temperature and/or overexertion.
  • Signs: hyperdynamic state (injected mucous membranes, hyperdynamic pulses, tachycardia), panting, vomiting or diarrhea, bleeding tendencies, CNS signs ranging from obtundation to coma and death.
  • Diagnosis: supportive history, elevated body temperature (if not cooled prior to presentation or in shock), development of multiple organ dysfunction (including acute kidney injury (AKI) and disseminated intravascular coagulation (DIC) and encephalopathic state).
  • Treatment: active cooling (generally to 39.4°C /103°F) and supportive therapies to prevent and treat systemic consequences.
  • Prognosis: guarded if prolonged hyperthermia.
    Print off the owner factsheet Heat stroke Heat stroke to give to your client.



  • Imbalance between heat load (eg environmental heat or that from metabolism or exercise) and heat dissipation (controlled by the hypothalamus).
    • Both non-exertional (classic) and exertional heat stroke are recognized in dogs.
  • Heat dissipating mechanisms in dogs and cats initially occur by radiation and convection through skin and evaporation through panting.
    • Peripheral vasodilation occurs to increase heat loss and cardiac output increases.
    • Cutaneous and splanchic pooling along with reduced circulating volume from severe dehydration can eventually lead to hypotension. This reduces the efficacy of heat disspitating mechanisms.
  • Core body temperature rises if heat dissipating mechanisms are not sufficient.
    • Direct thermal damage results in cellular necrosis, protein and enzyme denaturation, lipid membrane disruption, mitochondrial damage and altered protein synthesis.
    • Thermal damage also results in the release of cytokines from muscle and increased absorption of endotoxin from the gastrointestinal tract.
    • Cytokines and endotoxins excessively activate leukocytes and endothelial cells.
    • This results in cytokine release resulting in activation of coagulation systems and inhibition of fibrinolysis.
    • This hypercoagulable state and endothelial injury results in microthombosis, leading to disseminated intravascular coagulation and multiple organ dysfunction.
  • Protective mechanisms include production of acute phase proteins and increased expression of intracellular heat shock proteins which protect the cellular proteins against denaturation.
  • Acclimatization can take weeks but include adaptive physiological and behavioral changes including increased blood volume, increased GFR and increased cardiac output.

Body systems affected by heat stroke

  • Renal: acute kidney injury (AKI).
  • Central nervous system: neuronal necrosis, cerebral edema, hemorrhage or multifocal vascular thrombosis and infarction.
  • Respiratory: thermal and biochemical injury may lead to non-cardiogenic pulmonary edema Lung: pulmonary edema.
  • Cardiovascular: cardiac arrythmias Heart: dysrhythmia secondary to hypoperfusion, direct thermal injury, metabolic abnormalities or DIC Disseminated intravascular coagulation.
  • Gastrointestinal: intestinal ischemia may lead to intestinal permeability facilitating translocation of bacteria and endotoxin.

Predisposing factors


  • High environmental temperature/humidity.
  • Poor ventilation, ie dog locked in car.
  • Lack of acclimatization.
  • Breed.
  • Obesity.
  • Cardiac disease/failure to increase cardiac output.
  • Upper respiratory tract disease/abnormalities:


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Segev G, Bruchim Y, Berl N, Cohen A & Aroch I (2018) Effects of fenoldopam on kidney function parameters and its therapeutic efficacy in the management of acute kidney injury in dogs with heatstroke. JVIM 32(3), 1109-1115 PubMed.
  • Carter A J & Hall E J (2018) Investigating factors affecting the body temperature of dogs competting cross country (canicross) races in the UK. J Them Biol 72, 33-38 PubMed.
  • Bruchim Y, Kelmer E, Cohen A, Codner C, Segev G & Aroch I (2017) Hemostatic abnormalities in dogs with naturally occurring heatstroke. JVECC 27(3), 315-324 PubMed.
  • Bruchim Y, Ginsburg I, Segev G, Marisat A, Avital Y, Aroch I & Horowitz M (2017) Serum histones as biomarkers of the severity of heatstroke in dogs. Cell Stress and Chaperones 22(6), 903-910 PubMed.
  • Bruchim Y, Horowitz M & Aroch I (2017) Pathophysiology of heatstroke in dogs - revisited. Temperature 4(4), 356-370 PubMed.
  • Otto C M, Hare E, Nord J L, Palermo S M et al (2017) Evaluation of three hydration strategies in detection dogs working in a hot enviroment. Front Vet Sci 4(October), 1-10 PubMed.
  • Bruchim Y, Segev G, Kelmer E, Codner C, Marisat A & Horowitz M (2016) Hospitalized dogs recovery from maturally occurring heatstroke; does serum heat shock protein 72 can provide prognostic biomarker? Cell Stress and Chaperones 21(1), 123-130 PubMed.
  • Nielsen L K, Bracker K & Price L L (2015) Administration of fenoldopam in critically ill small animal patients with acute kidney injury: 28 dogs and 34 cats (2008-2012). JVECC 25(3), 396-404 PubMed.
  • Garber J B, Saile K, Rademacher N, Wignall J R, McLaughlin L D & Ryan K A (2015) Pneumothorax in a dog caused by necrotizing pneumonia secondary to heatstroke. JVECC 25(6), 759-764 PubMed.
  • Segev G, Daminet S, Meyer E, De Loor J, Cohen A, Aroch I & Bruchim Y (2015) Characterization of kidney damage using several renal biomarkers in dogs with naturally occurring heatstroke. Vet J 206(2), 231-235 PubMed.
  • Segev G, Aroch I, Savoray M, Kass P H & Bruchim Y (2015) A novel severity scoring system for dogs with heatstroke. JVECC 25(2), 240-247 PubMed.
  • Chen G M, Lan Y Y, Wang C F et al (2014) Clearance of serum solutes by hemofiltration in dogs with severe heat stroke. Scan J Trauma, Resuscitation and Emergency Medicine 22(1), 1-7 PubMed.

Other sources of information

  • Bruchim Y, Kelmer E (2018) Canine heat stroke. In: Drobatz K J et al. Textbook of Small Animal Emergency Medicine. Wiley and Sons.


Anesthetic monitoring: pulse oximetry

Anesthetic monitoring: urine output

Arterial blood gas sampling


Blood biochemistry: alkaline phosphatase (ALP)

Blood biochemistry: aspartate aminotransferase (AST)

Blood biochemistry: creatine phosphokinase

Blood biochemistry: creatinine

Blood biochemistry: gamma glutamyltransferase

Blood biochemistry: glucose

Blood biochemistry: potassium

Blood biochemistry: sodium

Blood biochemistry: total calcium

Blood biochemistry: urea

Brachycephalic obstructive airway syndrome (BOAS)


Diarrhea: chronic

Disseminated intravascular coagulation


Fibrin degradation products

Fluid therapy

Fluid therapy: for heat exhaustion


Gastric lavage

Heart: dysrhythmia

Hematology: activated clotting time

Hematology: activated partial thromboplastin time (APTT)

Hematology: D-dimers

Hematology: nucleated red blood cell

Hematology: packed cell volume

Hematology: prothrombin time






Immune-mediated thrombocytopenia

Kidney: acute kidney injury (AKI)

Kidney: advanced renal therapies

Larynx: paralysis

Liver: acute disease

Lung: aspiration pneumonia

Lung: pulmonary edema

Lung: pulmonary hemorrhage


Multiple organ dysfunction syndrome (MODS)


Nasal oxygen administration

Peritoneal dialysis


Plasma: fibrinogen

Poisoning: overview

Primary ciliary dyskinesia

Retriever: Labrador



Shock: cardiogenic

Shock: septic

Systemic inflammatory response syndrome (SIRS)


Trachea: collapse

Urinalysis: blood

Urinalysis: centrifuge sediment

Urinalysis: glucose

Urinalysis: protein

Urinalysis: specific gravity

Ventricular tachycardia


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