Vital Signs

Body Temperature



  • Human body temperature is a balance of heat production and heat dissipation, and tends to vary very little within an individual. Temperature is regulated by the hypothalamus, which drives thermoregulatory processes that include vasoconstriction / vasodilation, sweating and shivering.
      • Normal Range

      • 36.0 - 37.5°C

Measuring Temperature

  • There are a wide variety of methods for measuring body temperature, which may be non-invasive or invasive. The most commonly used methods in clinical practice tympanic and oral methods.
    • Methods of Measuring Body Temperature

    • Non-invasive

    • Orally - an electronic or chemical probe is placed underneath the tongue
    • Axillary - an electronic or chemical probe is placed in the axilla
    • Tympanic - an infrared probe is placed within the external auditory canal 
    • Forehead (non-contact) - an infrared scanner is pointed at the forehead
    • Rectally - an electronic or chemical rectal probe is placed within the rectum
    • Invasive

    • Urinary bladder - a probe is placed in the bladder with an indwelling catheterUsed in intensive care
    • Oesophageal - a probe is placed within the oesophagusUsed in intensive care
    • Ventricular - a probe is placed within the ventricle of the brainUsed in neurosurgical patients in intensive care
    • Pulmonary artery catheter - a probe is placed within the pulmonary arteryGold standard and not used clinically

Increased Body Temperature

  • Increased temperature most often is related to fevers, however it is important to consider non-inflammatory causes of hyperthermia.
    • Classification

    • Fever - 37.5 - 38.3°C
    • Hyperthermia - 38.4 - 39.9°C
    • Hyperpyrexia - 40 - 41°C
    • Extreme hyperpyrexia - >41.5°C
  • Fevers occur when the body's 'set point' of temperature is set to a higher level than normal. This results in responses aimed at increasing body temperature, including vasoconstriction and shivering.
  • Non-inflammatory hyperthermia occurs when there is an imbalance in heat production and heat dissipation.
    • Causes of Increased Body Temperature

    • Fever

    • Infection - bacterial, protozoal, fungal, viral
    • Auto-immune conditions - rheumatoid arthritis, SLE, thyroiditis
    • Thromboembolism - DVT / PE
    • Metabolic disorders - gout
    • Transfusion reactions
    • Abnormal hypothalamic function - stroke, encephalitis, head trauma
    • Non-Inflammatory Causes

    • Excessive heat production - exertion, thyrotoxicosis, phaeochromocytoma, status epilepticus, tetany
    • Poor heat dissipation - heat stroke, dehydration, autonomic dysfunction, excessive clothing
    • Drug-induced - aspirin, stimulants, anticholinergics
    • Malignant hyperthermia (rare reaction to inhaled anaesthetics)

Reduced Body Temperature

  • Hypothermia is a reduction in human body temperature. This tends to occur due to heat loss from exposure to cold, vasodilation or burns; hypothermia can also occur in the context of reduced heat production, or due to central temperature dysregulation.
    • Classification

    • Mild hypothermia - 34 - 35.9°C
    • Moderate hypothermia - 32 - 33.9°C
    • Severe hypothermia - 30.3 - 31.9°C
    • Profound hypothermia - <30°C
    • Causes of Hypothermia

    • Heat Loss

    • Exposure to cold - low ambient temperature, inadequate clothing, water immersion
    • Vasodilation - alcohol ingestion, sepsis, vasodilators
    • Skin loss - burns, dermatitis
    • Treatment for hyperthermia
    • Reduced Heat Production

    • Decreased metabolic rate - hypothyroidism
    • Decreased muscular activity - sedatives, opioids, muscle relaxants
    • CNS Temperature Dysregulation

    • Hypoadrenalism, hypopituitarism, head trauma, stroke
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