Hyperthermia- Fever


Elevation of body temperature above the set point is called hyperthermia, fever or pyrexia. 

Classification of Fever-

Fever is classified into three categories:-

  • Low-grade fever: When the body temperature rises to 38°C to 39°C, (100.4°F to 102.2°F)
  •  Moderate-grade fever: When the temperature rises to 39°C to 40°C (102.2°F to 104°F)
  • High-grade fever: When the temperature rises above 40°C to 42°C (104°F to 107.6°F).


Hyperpyrexia is the rise in body temperature beyond 42°C (107.6°F). Hyperpyrexia results in damage of body tissues. Further increase in temperature becomes life threatening. 

Causes of Fever-

  • Infection: Certain substances (pyrogens) released from bacteria or parasites affect the heat­regulating system in hypothalamus, resulting in the production of excess heat and fever.
  • Hyperthyroidism: Increased basal metabolic rate during hyperthyroidism causes fever
  • Brain lesions: When lesion involves temperatureregulating centers, fever occurs.
  • Diabetes insipidus: In this condition, fever occurs without any apparent cause.

Signs and Symptoms-

Signs and symptoms depend upon the cause of fever:- 

  •  Headache
  • Sweating
  • Shivering
  • Muscle pain
  • Dehydration
  • Loss of appetite
  • General weakness.

Hyperpyrexia may result in: