Definition of "Fever"

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Fever (aka pyrexia) is an elevated body temperature above the normal range of 37 ± 0.5°C, i.e. >37.5°C.

Patient information

I know fever means you're hot, but what does hot mean?
Normal temperature is 0.5°C above and below 37°C.

  • Fever occurs as a defence mechanism, as the body's immune response is stronger at higher temperatures, and it makes it more difficult for bacteria and viruses to survive
  • Where the fever lasts longer than the infection, an underlying disease is suggested

Patient information

Why do fevers happen?
It's apart of the body's defense system, because the immune system is more powerful at higher temperatures.


It should be considered an emergency, when kids:

  • <3 mo and >38°C. It is most concerning in very young babies
  • 3-6 mo and >39°C
  • >6 mo and shows other signs of unwell (floppy and drowsy)

However, because there is an increase in the regulatory set-point, although (actual) temperature increases, there is a general feeling of cold.

Afebrile means does NOT have fever.

  • Low grade fever, 37.5-38.5C
  • Fever, >38.5C
  • Infectious, including:
    • Viral, most commonly, including:
      • URTI's (cold, flu)
      • Gastroenteritis
      • Chickenpox
      • Infectious mononucleosis
      • Ebola virus
      • HIV
    • Bacterial, including:
      • Serious URTI's, such as strep throat, which needs to be Tx or can result in rheumatic fever or heart damage
      • Gastroenteritis
      • Lyme disease
      • Ear infections
      • Pneumonia, which may have stabbing chest pain, difficulty breathing
      • UTI's, which may have flank pain, vomiting
      • Meningitis, which may have neck stiffness, photophobia, vomiting, drowsiness, in infants <6mo the fontanelle can bulge. A rash can indicate a particular cause (e.g. meningicoccal)
      • Septicemia
    • Protozoa, including Malaria
  • Allergic reactions to drugs or vaccines
  • GI disease
  • Skin inflammations, including:
    • Boils
    • Abscess
  • Immunological diseases, including:
    • Lupus erythematosus
    • Sarcoidosis
    • Inflammatory bowel disease
    • Kawasaki disease
    • Autoimmune hepatitis
  • Chronic joint inflammation
  • Tissue destruction, including:
    • Hemolysis
    • Surgery
    • Infarction
    • Crush syndrome
    • Rhabdomyolysis
    • Cerebral bleeding
  • Blood disorders, including:
    • Reaction to incompatible blood products
  • Cancers, including:
    • Kidney cancer
    • Leukemia
    • Lymphoma
  • Metabolic disorders, including:
    • Gout
  • Thromboembolic processes, including:
    • PE
    • DVT
  • Idiopathic, known as fever of unknown origin (aka pyrexia of unknown origin) is where the patient has fever (an elevated temperature), but despite Ix by a doctor, no explanation has been found. It is a diagnosis of exclusion, requiring eliminating all possibilities until only 1 explanation remains

Patient information

What can cause hot temperature?
Infections is the biggie, so things like infection of the urinary system, tummy system, breathing system, ears, lungs, and brain. It can also occur in generalized infections like chickenpox, HIV. It can also happen in other diseases, of the tummy system, skin, blood, and metabolism. Cancers. Allergies, to drugs or vaccines.

  • Based upon pattern of temperature:
    • Continuous fever
    • Intermittent fever
    • Remittent fever
    • Pel-Ebstein fever
  • Hyperpyrexia, is a fever w/ an extreme elevation of body temperature 41.5°C+. It is considered a medical EMERGENCY, as it may indicate a serious underlying condition or lead to significant side effects. It is caused by:
    • Intracranial hemorrhage, commonly
    • Sepsis
    • Kawasaki syndrome
    • Neuroleptic malignant syndrome
    • Drug effects
    • Serotonin syndrome
    • Thyroid storm
    • Infections are the most common causes of fever, but as temperature rises, other cause become more common. Infections associated w/ hyperpyrexia include:
      • Roseola
      • Measles
      • Enteroviral infections
  • Febrile convulsions
  • Flushed, where skin might feel warm, but core temperature will be quite normal. This can occur when there is too much bedding, clothing, engaged in vigorous physical exercise, a very hot day
  • Hyperthermia, which is increase in body temperature above the body's regulatory set-point
  • Teething (usually only a mild raise in temperature, below 38°C)
  • Hx, including:
    • Onset and duration
    • Time, pattern, variation
    • Triggers, including drugs
    • Associated features, including:
      • Cough, sputum production, chest pain, SOB → infectious resp
      • Valve issues, palpitations, dental problems → infective endocarditis
      • Diarrhea, nausea, vomiting, abdominal pain → infectious GI
      • Headache, neck stiffness, photophobia → infectious CNS, including encephalitis, meningitis
      • Joint pain, skin lesions → connective tissue disease, vasculitis
      • IV devices, inflamed cannula sites
  • Place thermometer on the tongue for 2-3 minutes, or if that is difficult [in say a child], under the armpit [although measurement is less accurate]. It can also be taken by inserting rectally (uncomfortable), aurally (through the ear, but this can be a little inaccurate), and superficially using a temporal artery thermometer (swiping over the forehead)
  • Mercury thermometers are no longer recommended because there is a risk it can break and release poisonous mercury into the body

Patient information

What can you ask about a hot temperature?
When it started, how long it's gone for? What's happened over time? What causes it? You can also ask things that commonly happen with a high temperature. So things like a cough, sputum, or shortness of breath, can suggest something breathing related. Diarrhea, vomiting, and tummy pain can suggest it's related to the tummy system. Headache, neck stiffness, afraid of light, can suggest it's related to the brain system.

  • Except at very high temperatures, treatment is often unnecessary
  • Temperature can be reduced with paracetamol or ibuprofen, but should only be used when particularly distressed. Note that these medications are not useful in addressing febrile convulsions. Aspirin should not be provided to children [as it causes Reye's syndrome that affects the brain and liver]
  • Ensure adequate hydration [urine should be pale yellow]
  • Antipyretic medication can lower the temperature, to be administered routinely only in an extreme of >41C
  • Dress lightly
  • Do not actively cool
  • Stay away from school or work [as infectious cause is likely]
  • Where a child is playing and attentive, it is less likely they are seriously ill
  • Young pre-school children can have up to 5-10 infections each year
  • 4% of kids between 6 mo-5yo have febrile convulsions, and grow out of it by 4-5yo
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Definition of Fever | Autoprac

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