Hypothermia After Spinal Anesthesia: Incidence and Treatment

Hypothermia is a potential complication following spinal anesthesia that is often under-monitored. Some studies measure the incidence of perioperative hypothermia from spinal anesthesia as being as high as 91% (Cobb et al., 2016). This represents a significant threat to patient safety, as the human body relies on tightly regulated homeostatic mechanisms to maintain a core temperature between 36.0 and 37.5 degrees Celsius to protect essential metabolic and cellular processes. These concerns are particularly relevant in the context of anesthesia, since impaired metabolism of anesthetic agents can delay awakening and prolong post-operative recovery. 

During and after general anesthesia, in which hypothermia is a known and anticipated side effect, impaired body temperature regulation stems primarily from central physiology. Thermoregulation is controlled in the hypothalamus, specifically within the anterior and posterior nuclei. Because general anesthetics cross the blood–brain barrier, they impair hypothalamic thermoregulatory responses and lower the thresholds for vasoconstriction and shivering. As a result, patients lose the ability to appropriately conserve heat during surgery and recovery. 

Conversely, spinal anesthesia causes hypothermia through a different, more peripheral mechanism. Instead of primarily blunting central regulation, spinal anesthesia blocks regional sympathetic activation, which is normally responsible for triggering peripheral vasoconstriction to conserve heat. When this sympathetic outflow from the spine is inhibited, peripheral vasodilation occurs. This produces substantial core-to-peripheral heat redistribution, resulting in rapid body heat loss in the cooled environment of ORs and procedure rooms. Demonstrating this mechanism, one study found that administration of the vasoconstrictor phenylephrine reduced the magnitude of hypothermia in patients undergoing spinal anesthesia by counteracting peripheral vasodilation (Ikeda et al., 1999). 

Many risk factors influence the severity of perioperative heat loss. Some are non-modifiable variables, such as prolonged operative duration, extremes of age, low body mass, or pre-existing spinal cord injuries. However, other important factors are modifiable if high-risk patients are identified early. These include operating room ambient temperature, prolonged exposure to wet or fluid-soaked clothing, and the rapid administration of unwarmed intravenous fluids or irrigation solutions (Simegn et al., 2021). Inadequate perioperative temperature monitoring may further worsen these risks by delaying recognition of progressive hypothermia. 

If left unmanaged, the complications of perioperative hypothermia can become severe and potentially life-threatening. Beyond delaying anesthetic drug metabolism and prolonging recovery, even mild hypothermia impairs platelet function and coagulation pathways, significantly increasing surgical blood loss and the likelihood of needing transfusion. Furthermore, hypothermia increases the risk of surgical site infections by contributing to local tissue hypoxia and impaired immune function. It may also trigger postoperative shivering, which significantly increases myocardial oxygen consumption and can elevate the risk of cardiac complications in vulnerable patients. 

Fortunately, several targeted measures can reduce the incidence and severity of perioperative hypothermia. Identifying high-risk patients allows surgical teams to proactively adjust operating room ambient temperature and promptly remove wet clothing or linens. In addition, active warming interventions provide substantial protective effects. These measures include routine warming of intravenous and irrigation fluids, alongside the use of forced-air warming blankets before, during, and after surgery. Continuous perioperative temperature monitoring is also essential, as it enables clinicians to identify early downward temperature trends before clinically significant hypothermia develops. Ultimately, vigilant monitoring and timely intervention are critical to minimizing complications and improving overall surgical outcomes in patients undergoing spinal anesthesia. 

References 

1. Cobb, B., Cho, Y., Hilton, G., Ting, V., & Carvalho, B. (2016). Active Warming Utilizing Combined IV Fluid and Forced-Air Warming Decreases Hypothermia and Improves Maternal Comfort During Cesarean Delivery: A Randomized Control Trial. Anesthesia & Analgesia, 122(5), 1490-1497. https://doi.org/10.1213/ane.0000000000001181
2. Ikeda, T., Ozaki, M., Sessler, D. I., Kazama, T., Ikeda, K., & Sato, S. (1999). Intraoperative Phenylephrine Infusion Decreases the Magnitude of Redistribution Hypothermia. Anesthesia & Analgesia, 89(2), 462-465. https://doi.org/10.1097/00000539-199908000-00040  
3. Simegn, G. D., Bayable, S. D., & Fetene, M. B. (2021). Prevention and management of perioperative hypothermia in adult elective surgical patients: A systematic review. Annals of Medicine and Surgery, 72, 103059. https://doi.org/10.1016/j.amsu.2021.103059