Acute fever

Background

Definition

  • Defined as temperature ≥38°C (100.4°F).
  • Peripheral temperature is not clinically accurate and central measurements are the preferred means of determining fever.
    • Rectal or oral
    • Rectal temperatures should not be performed in neutropenic patients[1]

Clinical Features

  • Fever directly causes an increase in:[2]
    • Heart rate: 10 beats per minute per degree centigrade
    • Respiratory rate

Differential Diagnosis

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Fever

Infectious


Non-infectious

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DDx by Heart Rate

Every 0.55°C increase in temperature should → increase HR by ~10BPM

Evaluation

General Approach

  • History: duration, recent travel, sick contacts, immunocompromised status, medications, recent procedures/hospitalizations, indwelling devices
  • Physical exam: systematic search for source — HEENT (sinuses, pharynx, ears, dental), lungs, heart, abdomen, skin/wounds, GU, joints, spine
  • Not all fevers require a workup — well-appearing immunocompetent adults with clear viral URI symptoms may need only supportive care

Workup (when indicated)

  • Basic: CBC with differential, BMP, urinalysis, blood cultures (x2 if concern for bacteremia), CXR
  • Additional based on suspicion:
    • Lactate, procalcitonin — if sepsis suspected
    • Lumbar puncture — if meningitis/encephalitis suspected
    • CT imaging — guided by suspected source (abdomen/pelvis for abdominal source, CT chest for pulmonary, CT head if AMS)
    • LFTs, lipase — if hepatobiliary or pancreatic source suspected
    • Joint aspiration — if septic arthritis suspected
    • Wound cultures — if skin/soft tissue infection

Special Populations Requiring Lower Threshold for Workup

Management

  • Antipyretics:
    • Acetaminophen 650-1000 mg PO/IV q4-6h (max 4g/day)
    • Ibuprofen 400-800 mg PO q6-8h
    • Antipyretics improve comfort but do not treat the underlying cause
    • Fever itself is generally not harmful in immunocompetent adults (except in hyperthermia where temperature >41C/106F can cause organ damage)
  • Treat the underlying condition:
    • Empiric antibiotics if bacterial infection suspected — do not delay for cultures
    • Source control (I&D of abscesses, removal of infected lines/devices)
    • See specific disease pages for targeted management
  • Fluid resuscitation: Fever increases insensible losses; ensure adequate hydration
  • Avoid "fever phobia": In immunocompetent patients, aggressive fever treatment is not required and may mask clinical trends

Disposition

  • Admit:
    • Suspected sepsis or bacteremia
    • Immunocompromised with fever (neutropenic fever)
    • Hemodynamic instability
    • Identified source requiring IV antibiotics or surgical intervention
    • Unreliable follow-up with concerning clinical picture
  • Discharge:
    • Well-appearing with clear viral syndrome
    • Identified source amenable to outpatient treatment (uncomplicated UTI, mild cellulitis)
    • Reliable follow-up with clear return precautions
    • Return precautions: worsening symptoms, inability to tolerate PO fluids, rigors, altered mental status

See Also

External Links

References

  1. ↑ Niven DJ, Gaudet JE, Laupland KB, Mrklas KJ, Roberts DJ, Stelfox HT. Accuracy of Peripheral Thermometers for Estimating Temperature: A Systematic Review and Meta-analysis. Ann Intern Med. 2015;163(10):768-777. doi:10.7326/M15-1150.
  2. ↑ Davies P, Maconochie I. The relationship between body temperature, heart rate and respiratory rate in children. Emerg Med J. 2009 Sep;26(9):641-3. doi: 10.1136/emj.2008.061598.
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