Mechanism of Postoperative Shivering

Postoperative shivering, also referred to as postanesthetic shivering, is often cited as one of the leading discomforts for patients following general anesthesia.¹ According to some reports, anywhere between 20 and 70% of patients undergoing general anesthesia might experience this complication.² Shivering is the physiological response to cold or other stimuli (like illness or nervousness) that triggers involuntary muscle contractions to generate heat. Anesthesia and surgical operations introduce several factors that, through different mechanisms, can make postoperative shivering more likely.

The primary cause of postoperative shivering is the interference of anesthesia upon the body’s ability to regulate its own heat (thermoregulation), often resulting in perioperative hypothermia.¹ Under normal conditions, thermoregulation occurs via multiple mechanisms, many of which are affected or impaired by anesthesia. For instance, vasoconstriction, the narrowing of blood vessels, is a strategy used by the body to preserve heat in the body’s core when temperatures drop. However, many anesthetic drugs cause vasodilation, which produces the opposite effect: blood vessels widen, transferring heat away from the body’s core and towards the skin.³ Anesthesia can also lower the threshold at which the body initiates responses like vasoconstriction and shivering, producing an additional mechanism that may cause postoperative shivering under conditions that it would normally not occur.⁴

Severe blood loss during surgery can also result in a significant drop in body temperature and subsequent shivering. Significant hypovolemia, the reduction of circulating blood volume, leads to a dangerous drop in blood pressure and, in severe cases, the onset of hypovolemic shock. With this reduced blood flow, the body prioritizes keeping the brain and heart supplied with oxygen, lowering blood flow to the skin and extremities and potentially leading to shivering.⁵ Even if blood flow to other parts of the body remains steady during the operation, blood loss can occur because hypothermia disrupts platelets and coagulation by slowing down enzymes involved in the process.⁶

Finally, postoperative shivering can occur due to low operating room temperatures,and patients may lie still in cold temperatures for multiple hours. Though some operating rooms are maintained at temperatures of 70˚F or higher to prevent hypothermia, many are kept colder for the comfort of the surgical staff, who wear gowns and other layers of clothing. Patients, on the other hand, might be in the operating room for extended periods of time while wearing thin gowns.

Fortunately, there are many ways to counter perioperative hypothermia and postoperative shivering and ensure patients stay warm throughout their procedures. It is fairly standard to actively warm patients before, during, and after surgery to maintain an adequate body temperature. Patients can be warmed with blankets before surgery to ensure that they have a normal or even slightly elevated temperature.⁷ During surgery, there are several options for keeping patients warm, such as a forced-air warming blanket—which blows warm air over the patient—the use of warmed intravenous fluids, warming pads placed underneath the patient, and the use of warm, humidified oxygen to prevent heat loss through breathing. Many of these methods can also be implemented after surgery. Postoperative shivering can result from one or more of several possible mechanisms, but there are several sufficient ways to mitigate it and ensure patients are comfortable and safe.

References

1. Alfonsi, P. Postanaesthetic shivering: epidemiology, pathophysiology, and approaches to prevention and management. Drugs 61, 2193–2205 (2001), DOI: 10.2165/00003495-200161150-00004

2. Lopez, M. B. Postanaesthetic shivering – from pathophysiology to prevention. Rom J Anaesth Intensive Care 25, 73–81 (2018), DOI: 10.21454/rjaic.7518.251.xum

3. Anesthesia Considerations of Thermoregulation and Regional Anesthesia. McGraw Hill Medical https://accessanesthesiology.mhmedical.com/content.aspx?bookid=2979&sectionid=249588875.

4. Sessler, D. I. Perioperative thermoregulation and heat balance. The Lancet 387, 2655–2664 (2016), DOI: 10.1016/S0140-6736(15)00981-2

5. Hypovolemic Shock – an overview | ScienceDirect Topics. https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/hypovolemic-shock.

6. Wallner, B. et al. Hypothermia Induced Impairment of Platelets: Assessment With Multiplate vs. ROTEM—An In Vitro Study. Front. Physiol. 13, (2022), https://doi.org/10.3389/fphys.2022.852182

7. Hakim, M. et al. The Effect of Operating Room Temperature on the Performance of Clinical and Cognitive Tasks. Pediatr Qual Saf 3, e069 (2018), DOI: 10.1097/pq9.0000000000000069