What is the appropriate approach and symptomatic management for postoperative shivering (rigor) in a patient?

Approach and Symptomatic Management of Postoperative Shivering (Rigor)

For established postoperative shivering, immediately administer meperidine 25-50 mg IV, which stops shivering in nearly 100% of patients within 5 minutes and is the single most effective pharmacologic agent available. 1

Initial Assessment and Differential Diagnosis

When encountering a postoperative patient with shivering, rapidly assess the following:

• Measure core temperature to differentiate hypothermic from normothermic shivering, as hypothermia is the most common cause but shivering occurs even in normothermic patients 1
• Check for infection signs: temperature ≥38.0°C, wound appearance, respiratory status, IV site phlebitis, and symptoms of sepsis 1
• Assess pain control adequacy, as inadequate analgesia on postoperative day 2 can manifest as shivering 1
• Distinguish from seizure: shivering presents as bilateral, symmetric, rhythmic oscillatory movements that respond to warming and anti-shivering medications, whereas seizures show asymmetric, asynchronous movements that do not respond to these measures 2

Immediate Non-Pharmacologic Interventions

Start these measures while preparing pharmacologic treatment:

• Apply forced-air warming devices to actively warm the patient 1
• Warm the extremities (surface counterwarming), which reduces the shivering threshold by approximately 4°C per degree of mean skin temperature increase 3
• Administer warmed IV fluids if the patient is receiving fluid resuscitation 1, 3
• Ensure adequate ambient room temperature 3

Pharmacologic Management Algorithm

First-Line Treatment: Meperidine

Meperidine 25-50 mg IV is the drug of choice, with the following evidence:

• Stops shivering in nearly 100% of patients within 5 minutes 1, 3
• Approximately 2,800 times more effective at inhibiting shivering than predicted by its analgesic potency alone 1, 3
• Uniquely lowers the shivering threshold while directly suppressing shivering through mechanisms beyond analgesia 1, 3
• Number-needed-to-treat (NNT) of 1.3 at 5 minutes and 1.5 at 10 minutes 4

Caution: Exercise care in patients at risk for seizures, as meperidine lowers the seizure threshold 1

Alternative Pharmacologic Options

If meperidine is contraindicated or unavailable, consider these alternatives in order of efficacy:

Second-Line Options:

• Tramadol 35-220 mg IV: NNT of 2.2, with evidence of efficacy in prevention and treatment 5, 6
• Nefopam 10-20 mg IV: NNT of 1.7, more effective than meperidine or clonidine in one neurosurgical study (95% vs 32% and 40% respectively) 6, 7
• Clonidine 150 μg IV: NNT of 1.3 at 5 minutes, though associated with potential hemodynamic effects 4, 6
• Doxapram 100 mg IV: NNT of 1.7 at 5 minutes 4

Adjunctive Agents (insufficient as monotherapy):

• Magnesium sulfate 2-4 g bolus, then 1 g/h infusion: Safe adjunct but inadequate alone for clinically significant shivering; maintain serum levels <4 mg/dL 1, 3
• Acetaminophen: Non-sedating adjunct but typically insufficient alone 3

Sedative/Analgesic Approach

For patients requiring deeper sedation or with refractory shivering:

• Continuous opioid infusion (fentanyl or hydromorphone) at moderate doses 3
• Add short-acting sedative (dexmedetomidine or propofol) titrated to minimum effective dose 3
• Avoid propofol or dexmedetomidine as first-line in hemodynamically unstable patients due to hypotension risk 3

Last Resort: Neuromuscular Blockade

For refractory shivering unresponsive to pharmacologic measures:

• Cisatracurium 0.1-0.2 mg/kg bolus, then 0.5-10 μg/kg/min infusion is the most effective abortive measure 3
• Preferred due to non-enzymatic plasma degradation, making it safe in renal and hepatic impairment 3
• Particularly appropriate when active temperature management is expected to be transient 1

Cause-Specific Management

Hypothermia-Related Shivering

• Continue active warming with forced-air devices until normothermia achieved 1
• Remember that delayed hypothermia can occur on postoperative day 2 due to heat redistribution from core to periphery 1

Pain-Related Shivering

• Administer NSAIDs if not contraindicated 1
• Ensure regular (not as-needed) pain medication administration 1

Infection-Related Shivering

• Obtain blood cultures if temperature ≥38.0°C 1, 3
• Initiate appropriate antibiotics if infection suspected 1
• Provide supportive care including hydration and oxygenation 1
• Rule out respiratory infections, wound infections, and phlebitis 1

Critical Pitfalls to Avoid

• Do not rely on acetaminophen or magnesium alone for clinically significant shivering—these are adjuncts only 3
• Do not delay meperidine administration while attempting less effective measures in symptomatic patients 1
• Do not miss early infection, as temperature spikes with shivering may be the first sign requiring prompt evaluation 1
• Do not use excessive sedation when simpler measures (meperidine + warming) are highly effective 1

Special Populations

• Sickle cell disease patients: Require particular attention as shivering can precipitate sickling crisis 1
• Neuraxial anesthesia patients: May experience delayed shivering on day 2 as the block wears off 1
• Post-cardiac arrest or brain injury patients: Shivering doubles metabolic rate and nearly triples oxygen consumption, worsening secondary injury 3