What are the non‑febrile causes of chills (rigors) in a patient with a normal body temperature?

Non-Febrile Chills: Causes and Clinical Approach

Chills with normal body temperature occur primarily through three mechanisms: thermoregulatory dysfunction (shivering triggered at abnormal temperature thresholds), stress-induced autonomic responses, and early infection before fever develops.

Primary Mechanisms of Non-Febrile Chills

Thermoregulatory Threshold Dysregulation

• The hypothalamic shivering threshold is normally triggered at 35.5–36°C, but this set point can be altered by brain injury, medications, or physiological stress 1
• Following hypoxic-ischemic injury or in certain neurologic conditions, the temperature threshold can shift lower, meaning patients may shiver even when core temperature appears normal by standard measurement 1
• Shivering represents involuntary muscle contractions that increase metabolic rate 2–6 fold, and can occur as a physiological response even when measured temperature is within normal range 2, 3

Stress-Induced Temperature Dysregulation

• Psychological or physiological stress activates the dorsomedial hypothalamus-sympathetic nerve axis, producing subjective sensations of cold and shivering independent of actual core temperature 4
• Chronic stress can reduce diurnal temperature variation and produce anticipatory temperature responses that manifest as chills without documented fever 4
• Autonomic responses to stress are proportional to changes in both internal and mean skin temperatures, not core temperature alone 2

Early or Occult Infection

• Elderly patients and immunocompromised individuals may present with chills as an early sign of sepsis before fever develops, or may exhibit hypothermia rather than fever during serious infection 5
• The CDC emphasizes that atypical temperature patterns in elderly patients require immediate evaluation for sepsis, including blood cultures, complete blood count, and urinalysis before antibiotic initiation 5

Specific Clinical Scenarios

Post-Operative or Post-Anesthetic Shivering

• Redistribution of heat from core to periphery can cause delayed hypothermia and shivering on postoperative day 2, even when core temperature measurement appears normal 6
• Reduction in sedative medications that were suppressing the shivering response can unmask thermoregulatory instability 6
• Inadequate pain control manifests as shivering through autonomic activation 6

Medication-Related Causes

• Drugs affecting the hypothalamic thermostat (opioids, sedatives, magnesium) alter the shivering threshold by 2–3°C, meaning patients may shiver at temperatures previously tolerated 1
• Withdrawal from medications that suppress shivering (benzodiazepines, propofol) can precipitate rebound shivering at normal temperatures 1

Peripheral Vasoconstriction Without Core Hypothermia

• Cold exposure triggers cutaneous vasoconstriction through both reflex and local cooling mechanisms, producing subjective chills even when core temperature remains normal 7, 3
• The extremities exhibit pronounced vasoconstriction while the head-neck region does not, creating temperature gradients that trigger shivering responses 3

Diagnostic Approach

Immediate Assessment

• Measure core temperature using esophageal, bladder, or properly placed oral probes—avoid axillary measurements which read 1.5–1.9°C below actual core temperature 8
• Assess for infection signs: altered mental status, wound examination, respiratory status, IV site evaluation 6, 5
• If elderly or immunocompromised, obtain blood cultures, complete blood count with differential, comprehensive metabolic panel, and urinalysis urgently 5

Red Flags Requiring Emergency Evaluation

• Altered mental status with chills suggests sepsis or heat-related illness 5
• Recent heat exposure with inability to cool down indicates heat exhaustion progressing to heat stroke 5
• Leukopenia, thrombocytopenia, or elevated liver enzymes in elderly patients with chills mandate immediate sepsis workup 5

Management Algorithm

Step 1: Rule Out Life-Threatening Causes

• If infection suspected with high probability, initiate broad-spectrum antibiotics immediately after cultures are obtained—do not delay for procalcitonin results 5
• If hyperthermia with altered mental status, activate emergency response and begin immediate cooling to target core temperature <39°C 5

Step 2: Address Thermoregulatory Dysfunction

• For shivering with normal core temperature, meperidine 25–50 mg IV is the most effective treatment, stopping shivering in nearly 100% of patients within 5 minutes 6
• Implement active forced-air warming to normalize peripheral temperature and reduce autonomic drive for shivering 6
• Ensure adequate pain control with scheduled (not as-needed) analgesics 6

Step 3: Adjunctive Measures

• Magnesium sulfate and acetaminophen provide modest benefit but are insufficient as monotherapy 1
• Skin counterwarming of extremities (ears, palms, soles) reduces shivering threshold by affecting cutaneous temperature sensors 1

Critical Pitfalls to Avoid

• Never rely on clinical appearance or peripheral temperature measurement alone—core temperature measurement is mandatory 8
• Do not dismiss chills in elderly patients as benign even with normal temperature; this may represent atypical infection presentation 5
• Avoid assuming shivering always indicates hypothermia; stress, pain, and early infection produce shivering at normal temperatures 4
• Do not delay antibiotics in suspected sepsis waiting for temperature elevation—chills may precede fever by hours 5