Causes of Shivering in Spinal Anesthesia
Hypothermia is the primary cause of shivering during spinal anesthesia, resulting from impaired thermoregulation, peripheral vasodilation, and redistribution of body heat from core to peripheral compartments. 1, 2
Primary Mechanism: Thermoregulatory Disruption
Spinal anesthesia fundamentally disrupts normal temperature regulation through several interconnected mechanisms:
- Peripheral vasodilation occurs below the level of the block, causing redistribution of body heat from central (core) to peripheral compartments 3
- Impaired thermoregulatory control results when the hypothalamic temperature setpoint is disrupted, triggering shivering when core temperature falls below approximately 35.5-36°C 2
- Loss of vasoconstriction response in blocked areas prevents the body's normal heat conservation mechanisms 4
Contributing Environmental and Iatrogenic Factors
Beyond the direct effects of spinal anesthesia, several modifiable factors increase shivering risk:
- Inadequate intraoperative warming through failure to maintain normothermia during surgery 1, 2
- Cool operating room environment with ambient temperature exposure 5
- Administration of unwarmed intravenous fluids 6
- Prolonged surgical exposure of large body surface areas 1
- Skin exposure in the operating theater environment 6
Metabolic Consequences
The metabolic impact of shivering is clinically significant and potentially dangerous:
- Oxygen consumption increases up to 500% during active shivering 7
- Metabolic rate can double or triple depending on muscle mass, creating significant cardiorespiratory stress 2
- Particular risk exists for patients with coronary artery disease, cardiopulmonary insufficiency, anemia, or debilitated status 7
Clinical Differentiation
It is critical to distinguish true thermoregulatory shivering from other causes:
- Non-thermoregulatory shivering can occur even with normal core temperature due to altered hypothalamic function following the neuraxial block 2
- Pain-related shivering may manifest from inadequate analgesia 1
- Early infection can present with temperature spikes and associated shivering, requiring prompt evaluation 1
Prevention Strategies
Active warming is the cornerstone of prevention and should be implemented proactively 4:
- Pre-warming the patient for 15 minutes before spinal anesthesia administration using forced-air warming devices, cotton blankets, or gown warming 6
- Maintaining intraoperative normothermia through forced-air warming systems 4, 5
- Administering warmed intravenous fluids 5, 6
- Controlling ambient operating room temperature 1
Pharmacologic Treatment When Shivering Occurs
Meperidine (25-50 mg IV) is the most effective medication for treating established shivering 4, 1:
- Meperidine is superior to other opioid agonists or agonist-antagonists for shivering reduction 4
- Intrathecal meperidine (0.2 mg/kg) can be added prophylactically to the spinal anesthetic, reducing shivering incidence from 56.7% to 16.7% 8, 7
Alternative pharmacologic options when meperidine is contraindicated include:
- Low-dose ketamine (0.5 mg/kg IV) reduces shivering incidence to 8% but may cause behavioral changes and nystagmus 3
- Tramadol (0.5 mg/kg IV) reduces shivering to 16% with fewer side effects than ketamine 8, 3
- Ondansetron (8 mg IV) reduces shivering incidence to 15% 8
- Dexamethasone, magnesium sulfate, clonidine, or dexmedetomidine are additional options 6
Critical Clinical Caveat
Hypothermia should always be treated by rewarming first 4. Pharmacologic agents should be reserved for situations where active warming is insufficient or when immediate control is needed for patients with cardiorespiratory compromise. The Task Force emphasizes that treating the underlying cause (hypothermia) takes precedence over symptomatic suppression of shivering 4.