What are the causes of shivering in spinal anesthesia?

Causes of Shivering in Spinal Anesthesia

Shivering during spinal anesthesia is primarily caused by perioperative hypothermia, which occurs in 50-80% of patients undergoing neuraxial anesthesia, triggered by disruption of normal thermoregulatory mechanisms and heat redistribution from core to periphery. 1

Primary Mechanism: Hypothermia-Induced Thermoregulatory Dysfunction

Spinal anesthesia disrupts the temperature setpoint in the preoptic region of the hypothalamus, lowering the threshold at which shivering is triggered (typically below 35.5-36°C). 2 This occurs through several mechanisms:

• Sympathetic blockade causes peripheral vasodilation, leading to rapid redistribution of core body heat to the periphery, resulting in a 0.5-1.5°C drop in core temperature within the first 30-60 minutes 1, 2
• Impaired vasoconstriction below the level of the block prevents the body's normal compensatory mechanism to preserve core temperature 2
• Loss of sensory input from blocked dermatomes prevents the patient from perceiving cold and requesting warming measures 1

Contributing Environmental and Procedural Factors

The operating room environment significantly exacerbates heat loss:

• Cool ambient operating room temperatures (typically 20-21°C) accelerate heat loss through radiation and convection 1
• Surgical exposure of large body surface areas increases evaporative and convective heat loss 1, 3
• Administration of unwarmed intravenous fluids directly cools core temperature 4
• Prolonged surgical duration allows progressive heat loss despite compensatory mechanisms 3

Metabolic Consequences of Shivering

Shivering doubles metabolic rate and can nearly triple oxygen consumption, creating significant physiological stress 2:

• Increased myocardial oxygen demand poses particular risk in patients with coronary artery disease or limited cardiopulmonary reserve 5
• Oxygen consumption can increase up to 500%, which is detrimental in patients with anemia or debilitated status 5
• Elevated metabolic expenditure can trigger demand ischemia in vulnerable patients 2

Secondary Non-Thermal Causes

While hypothermia is the dominant cause, other factors can trigger or exacerbate shivering:

• Pain-related shivering may occur with inadequate analgesia, though this is less common during the intraoperative period 3
• Early infection can present with temperature spikes and associated shivering, though this typically manifests postoperatively rather than intraoperatively 3
• Medication effects, particularly as sedatives wear off, may unmask shivering that was previously suppressed 3

Risk Stratification

Patients at highest risk for shivering during spinal anesthesia include:

• Those with inadequate active warming measures during the perioperative period 3
• Elderly patients, who have impaired thermoregulatory responses 6
• Patients undergoing prolonged procedures with extensive surgical exposure 3
• Patients with sickle cell disease, where shivering can precipitate sickling crisis 2

Clinical Pitfalls to Avoid

Do not assume shivering is benign or self-limited—it indicates failed thermoregulation and carries metabolic consequences that can worsen outcomes, particularly surgical site infection risk, myocardial ischemia, and coagulopathy 1. The key error is failing to implement active warming measures prophylactically rather than waiting to treat shivering reactively 1.