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
- Increased Metabolic Rate & Oxygen Demand
- 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