On Call: Fever

Causes

Fever Definition

  • The Exact Definition of Fever Varies
  • Most Common Threshold: Temperature ≥ 38°C (100.4°F)
    • May Also Consider Temperature ≥ 100.0°F (37.8°C)
  • Elderly Have Impaired Ability to Mount a Fever Response & Lower Temperatures May Still Indicate a Fever
  • Regulated by Hypothalamus with a Raised “Set Point” from Prostaglandins
    • Triggers by Cytokines & Toxins
  • Sepsis Causes 74% of Fevers in Hospitalized Patients

Other Definitions

  • Hyperthermia – Uncontrolled Temperature Elevation Not Regulated by the Hypothalamus
    • Causes: Heat Stroke, Malignant Hyperthermia, Neuroleptic Malignant Syndrome, Drugs
    • Can Be Rapidly Fatal
  • Hyperpyrexia – Exceptionally High Fever (> 41.5°C)

Effects of Fever

  • Symptoms:
    • Headache
    • Generalized Discomfort
    • Body Aches
    • Lethargy
  • Negative Physiologic Effects:
    • Increased Metabolic Rate & Oxygen Demand
      • Can Exacerbate Cardiac or Pulmonary Insufficiency
    • Cellular Damage
    • Increased Bacterial Translocation in the Gut
  • Beneficial Effects:
    • Slows Bacterial Growth
    • Enhances Immune System

Measurement/Thermometry

  • Peripheral Measurement
    • More Convenient but Less Accurate
    • Methods: Oral, Axillary & Temporal
  • Central Measurement
    • More Accurate but Less Practical
    • Are Often Slightly Higher than Peripheral Measurements
    • Methods: Rectal, Esophageal, Urinary Bladder & Pulmonary Artery Catheter

Management

Evaluation for Fever of Unknown Origin

  • History & Physical Exam
  • Complete Blood Count (CBC)
  • Blood Culture – 2-3 Drawn from Separate Sites
  • Urinalysis with Reflex to Urine Culture
  • Chest X-Ray (CXR)
  • Consider Direct CT Scanning

General Treatment

  • Primary Treatment: Antipyretics
    • Primary Treatment for Fever but Not Effective for Hyperthermia (Hypothalamic Set Point is Not the Cause)
    • Should Allow Permissive Fever for Asymptomatic Infection-Related Fevers
    • Primary Indications for Treatment of Fever:
      • Moderate-Severe Symptoms
      • Critically Ill with Cardiopulmonary Compromise
  • Adjuncts:
    • Cooling Blankets
    • Cool (Not Cold) Sponge Baths
    • If Cold Fluids are Used, Do Not Use a Central Line Close to the Heart
  • Treat Any Underlying Cause of Hyperthermia

Antipyretics

  • Acetaminophen (Tylenol)
    • Generally Preferred Over NSAIDs Due to GI & Platelet Effects
    • Oxidized in the Brain & Then Inhibits COX to Lower the Hypothalamic Set Point
  • NSAIDs
    • Mechanism: Inhibits Cyclooxygenase (COX) to Lower the Hypothalamic Set Point
    • Aspirin Has Shown Equivalent Efficacy to Tylenol in Reducing Fever at Similar Doses
  • *See Pharmacology & Anesthesia: Nonnarcotic Analgesia