What is the management of rigors (shivering) without fever?

Management of Rigors Without Fever

The primary management of rigors without fever requires accurate core temperature measurement to rule out occult hypothermia or infection, followed by targeted treatment with meperidine (first-line) or alternative opioids combined with non-pharmacologic warming measures, while simultaneously investigating the underlying cause.

Initial Assessment and Temperature Verification

The first critical step is obtaining an accurate core temperature measurement, as peripheral measurements can be misleading:

• Use esophageal or nasopharyngeal temperature monitoring as these provide the most accurate core temperature readings, superior to axillary, rectal, or tympanic measurements 1
• Axillary temperatures can read 1.5-1.9°C below actual core temperature, potentially masking hypothermia 1
• Bladder and rectal measurements have up to 1°C variability and lag behind true core temperature 1

Key diagnostic consideration: Rigors without documented fever may represent:

• Occult hypothermia triggering compensatory shivering 1
• Early bacterial infection before fever develops (66% of children with rigors have bacterial infections, with significantly higher positive blood culture rates) 2
• Medication-induced rigors (particularly with IL-2 therapy or certain antidepressants) 1, 3

Immediate Management Algorithm

Step 1: Non-Pharmacologic Interventions (Initiate First)

• Apply skin counterwarming to extremities, particularly ears, palms, and soles using air-circulating blankets 1, 4
• Each 4°C increase in mean skin temperature reduces the shivering threshold 1
• Maintain ambient temperature control and prevent further heat loss 1

Step 2: First-Line Pharmacologic Treatment

Meperidine is the drug of choice for rigors/shivering control:

• Dose: 25-50 mg IV bolus 4, 5
• Most effective agent for lowering shivering threshold and suppressing rigors 1, 4
• Controls rigors in 73-83% of cases with onset of action in 1.8-2.1 minutes 5
• Caution: Avoid in patients at risk for seizures or those not continuously monitored 1

Alternative opioids if meperidine contraindicated:

• Butorphanol 1 mg IV (83% effective, 2.1 minute onset) 5
• Tramadol 50 mg IV (73% effective, 1.8 minute onset) 5
• Fentanyl (dose titrated to effect) 4

Step 3: Adjunctive Non-Sedating Agents

Add these medications for synergistic effect without significant sedation:

• Acetaminophen 650-1000 mg PO/IV - safe antipyretic with favorable profile 6, 7
• Magnesium sulfate 2-4 g IV (maintain serum levels <4 mg/dL) - modest effect but excellent safety profile 1, 4
• Buspirone 30 mg PO - can reduce shivering threshold to 33°C when combined with meperidine, without primary sedation concerns 1, 8

Step 4: Escalation for Refractory Rigors

If rigors persist despite above measures:

• Dexmedetomidine infusion - effective for shivering control with less respiratory depression than other sedatives 4, 7
• Midazolam - for additional sedation if needed 4
• Neuromuscular blocking agents - ONLY as last resort after ensuring adequate sedation depth 1, 4

Critical Diagnostic Workup

While initiating symptomatic treatment, simultaneously investigate underlying causes:

Laboratory evaluation:

• Complete blood count with differential (absolute band count >1500/mm³ significantly increases bacterial infection risk) 2
• Blood cultures (higher yield in patients with rigors) 2
• Comprehensive metabolic panel 1
• Core temperature monitoring every 2-4 hours 1

Consider infectious workup: The presence of rigors increases the relative risk of bacterial infection by 1.35-fold, particularly when combined with elevated band count 2. Empiric antibiotics should be strongly considered pending culture results.

Special Considerations and Pitfalls

Common pitfalls to avoid:

• Do not use anticholinergics simultaneously with or after alpha-2 agonists like dexmedetomidine, as this can cause adverse cardiovascular effects including tachycardia, prolonged hypertension, and arrhythmias 9
• Avoid NSAIDs as monotherapy - while listed as first-line in some protocols, they have modest efficacy and should be combined with other agents 1
• Do not assume absence of fever excludes infection - rigors may precede measurable fever, especially in bacterial infections 2

Medication-induced rigors: Review medication list for causative agents including SSRIs, SNRIs, beta-blockers, calcium channel blockers, and antipsychotics 3. Consider dose reduction or alternative agents if medication-induced.

Monitor for complications: Rigors can cause negative pressure pulmonary edema through transient laryngeal dyskinesia and increased work of breathing, presenting as acute hypoxic respiratory failure with stridor 10. This requires immediate supportive care and treatment of underlying rigors.

Metabolic impact: Shivering doubles metabolic rate and nearly triples oxygen consumption, potentially causing cerebral metabolic stress and demand ischemia 1. Prompt control is essential to prevent secondary injury.