Heat Stroke

Heat Stroke is a special state of acute hyperthermia resulting from defects in the heat regulatory mechanism against extreme environmental heat.

Heat stroke is also known as heat stress, heat prostration, malignant hyperthermia, etc.

Susceptibility for Heat Stress

• Dogs and cats have poor thermoregulatory mechanism and in dogs sweating is absent, hence they are more susceptible.
• In sheep: due to heavy wool it is also susceptible, hence summer shearing is done.
• Pigs: limited lung capacity and heavy subcutaneous fat in pig makes more susceptible.

During increased environmental temperatures, there is panting due to limited lung capacity, resulting in increased respiratory contractions and increased body temperature. Purebred cattle like HF and Jersey have poor thermoregulatory mechanisms because of their adaptation to temperate climates.

Factors responsible for Heat Stroke

• Extreme environmental temperature
• High humidity in the environment
• Over crowding
• Transportation during high environmental temperature
• Limited supply of water
• Young ones and saline are less accommodative for heat regulation and so susceptibility maximum
• Obese animals have less heat loss so have increased body temperature

Pathogenesis

Heat stroke → damage to CNS → tachycardia → dyspnea → convulsions → unconsciousness → respiratory failure → death

Exposure to high environmental temperatures results in the inability of the hypothalamus to cope with the increased temperature, hence the increase in the set point, as a consequence of which tachycardia develops, increased renal retention (dyspnea), decreased filling time in the heart, and low oxygenated blood in the lungs, which create a state of hypoxia and hypoglycemia that is more pronounced on the centres in the brain. The outcome is convulsions (called hyperpyrexic convulsions, most common in pups) and sometimes unconsciousness, and in extreme conditions, the respiratory centre fails, leading to death.

Clinical Signs of Heat Stroke

• Dull and depression
• Rapid breathing
• Open mouth breathing – protrusion of tongue
• Frothy discharge from mouth and nostrils – congestion of mucus membrane
• Tachycardia – cardiac arrhythmia
• Temperature is high as 106 to 110 °F cause convulsions
• Paralysis of respiratory and motor centres
• Coma and Death

Management and treatment of Heat Stroke

• Animal should be kept in well ventilated place and arrangement of fan or AC if possible. Crowding around the animal should be avoided.
• Sprinkling of cold water is advised. By this, temperature can be reduced by 20F. Sprinkling should be at highly vascular areas. It should be preferably on head, rump, back and inguinal region.
• Sometimes cold water enema may lead to increased dissipation of heat from the body. IV fluids based on electrolytes, CVP and hydration status.
• Application of icepacks on back or rump, axillary and inguinal region
• Provide cold water for drinking or ice cube for licking
• Animal should be sedated by using tranquilizers resulting in decreased activity of animal that in turn causes lowered BMR ending in decreased body temperature.

Tranquilizers used in various animals in heat stroke conditions are:

• Triflupromazine: 0.2mg / kg b.wt for cattle
• Xylazine: 1.1mg / kg b.wt for horse
• Diazepam: 0.25 mg / kg b.wt for dogs

Corticosteroids can be administered to prevent hypothermic shock are:

• Dexamethasone: 0.5 – 1.0 mg / kg b.wt ( long acting and more potent)
• Hydrocortisone: 5.0 – 10 mg /kg b.wt (short acting and less potent)

Antihistamines like pheneramine maleate / chlorpheneramine maleate can be given; once the temperature comes with in manageable range antipyretics can be given:

• Acetyl salicylic acid
• Sodium salicylate
• Analgin or Paracetamol (tab or injection every 6 hours)

Broad spectrum antibiotics are given to avoid secondary bacterial infection because in heat stroke there will be lowered immunity.