- 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.
- 36.0 - 37.5°C
- 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
- 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
- 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.
- 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
- 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
- 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.
- 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
- 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