What are the causes of acute onset shivering in an adult patient with no significant past medical history?

Causes of Acute Onset Shivering

Acute onset shivering in an adult with no significant past medical history is most commonly caused by hypothermia (core temperature below 35.5-36°C), infection/sepsis, or postoperative/post-anesthesia thermoregulatory response.

Primary Physiological Mechanism

• Shivering represents a thermoregulatory response triggered by the preoptic region of the hypothalamus when core temperatures fall below 35.5-36°C 1
• This involuntary oscillatory skeletal muscle activity generates heat but doubles metabolic rate and nearly triples oxygen consumption 1
• The absence of shivering in cold environments should be considered a warning sign for severe hypothermia or thermoregulatory failure 2

Infectious/Inflammatory Causes

• Infection is a leading cause of acute shivering, particularly respiratory and wound infections 3
• Sepsis should be suspected when shivering occurs with temperature ≥38.0°C and requires prompt evaluation within 1 hour 3
• Cytokine release from surgical procedures can trigger shivering independent of core temperature 4
• Fever represents a regulated upward shift in hypothalamic set-point with intact thermoregulatory mechanisms, distinct from hyperthermia 5

Iatrogenic/Situational Causes

Post-Anesthesia/Postoperative

• Postoperative shivering occurs in response to intraoperative hypothermia and is the most common cause in surgical patients 4, 6
• Inadequate intraoperative warming and prolonged surgical exposure are primary risk factors 3
• Acute opioid withdrawal from short-acting narcotics can trigger non-thermoregulatory shivering even in normothermic patients 6
• Postoperative pain itself can cause non-thermoregulatory tremor 4

Therapeutic Hypothermia/Temperature Management

• Post-cardiac arrest patients undergoing targeted temperature management (TTM) commonly experience shivering, particularly during the induction phase 1
• Shivering during TTM increases cerebral metabolic rate when oxygen delivery may already be compromised, potentially causing secondary cerebral injury 1
• Reduction of sedative medications that were suppressing shivering response can unmask shivering 3

Critical Thermoregulatory Failure

• Acute illnesses including pneumonia, congestive heart failure, renal failure, drug overdose, and hypoglycemia can cause thermoregulatory failure with absent shivering response 7
• This represents a life-threatening condition requiring immediate recognition 7
• Patients with thermoregulatory failure may present with hypothermia, metabolic acidosis, altered sensorium, and bradyarrhythmias 7

Risk Factors for Increased Shivering

• Younger age, male sex, and decreased body surface area are associated with more intense shivering responses 8
• Healthier individuals and those with milder brain injury experience more vigorous shivering 1
• Conversely, severe brain injury following hypoxic-ischemic injury can lower the temperature threshold for shivering or eliminate it entirely 1

Metabolic Consequences Requiring Urgent Intervention

• Shivering-induced elevated metabolic expenditure can trigger bioenergetic failure with demand cerebral ischemia 1
• Significant mismatch between energy supply and demand to the brain occurs during shivering 1
• This is particularly dangerous in patients with compromised cardiac output or acute brain injury 1

Clinical Pitfalls to Avoid

• Do not assume normothermia based on peripheral temperature measurements alone—use core temperature monitoring (esophageal, bladder, or pulmonary artery thermistors) when accurate assessment is critical 1
• Do not overlook infection as the cause—obtain blood cultures and initiate empiric antibiotics within 1 hour if sepsis is suspected 1
• Do not dismiss shivering in normothermic patients as benign—consider non-thermoregulatory causes including pain, opioid withdrawal, and cytokine release 4, 6
• Recognize that healthy volunteers exposed to cold, wet, windy conditions maintained normal core temperature for 3 hours due to shivering thermogenesis—therefore absence of shivering in cold environments indicates impending or established hypothermia 2

Algorithmic Approach to Acute Shivering

1. Measure core temperature accurately using esophageal, bladder, or rectal thermometry 1
2. If temperature <35.5°C: Diagnose hypothermia and initiate rewarming based on whether thermoregulatory mechanisms are intact 7
3. If temperature ≥38.0°C: Suspect infection/sepsis, obtain blood cultures, and initiate antibiotics within 1 hour 1, 3
4. If normothermic (36-37.5°C): Evaluate for non-thermoregulatory causes including postoperative pain, opioid withdrawal, or cytokine release 4, 6
5. If post-cardiac arrest or brain injury: Recognize that altered hypothalamic function may lower shivering threshold or eliminate it entirely 1