Post-anesthesia shivering (PAS) is an uncontrolled trembling or muscle hyperactivity that commonly occurs after surgery. It is a frequent occurrence in the post-anesthesia care unit, with reported incidence rates ranging from 5% to 65% after general anesthesia and 30% to 60% following regional anesthetic procedures like epidural or spinal anesthesia. PAS is a common, temporary side effect of anesthesia.
Understanding How Long Shivering Typically Lasts
Most instances of shivering stop within 20 to 30 minutes. However, some patients may experience chills and shivering for a few minutes to several hours. The duration can vary depending on several factors, including the type of anesthesia administered, the length of the surgical procedure, and individual patient characteristics.
For example, longer operations and orthopedic procedures may be associated with an increased risk of shivering. Younger patients and those with a lower body mass index (BMI) might also experience shivering more frequently or for a slightly longer duration. Healthcare providers closely monitor patients in the recovery room to ensure their safety and comfort as the shivering subsides.
The Science Behind Post-Anesthesia Shivering
Shivering after anesthesia is primarily a physiological response to changes in body temperature and the effects of anesthetic agents. During surgery, patients often experience a drop in their core body temperature, known as perioperative hypothermia, due to exposure to a cool environment in the operating room. Anesthetic drugs and gases further contribute to this by impairing the body’s natural ability to regulate its temperature. This impairment occurs because anesthetics can cause blood vessels to widen, leading to heat redistribution from the core of the body to the skin, and they can also inhibit the brain’s thermoregulatory centers.
The body’s central thermoregulation system, primarily controlled by the hypothalamus, attempts to maintain a stable core temperature. When this system is disrupted by anesthesia, the body loses heat. Shivering is the body’s involuntary attempt to generate heat through muscle contractions to raise its core temperature back to normal. In some cases, shivering can also occur even in patients with normal body temperatures, possibly influenced by factors like pain or the effects of anesthetic drugs on spinal reflexes.
Strategies for Comfort and Prevention
Medical staff employ strategies to minimize and manage post-anesthesia shivering. Keeping patients warm before, during, and after surgery is a primary approach. This includes using warming blankets and forced-air warming devices in the recovery area. Heating intravenous fluids before administration also helps to maintain body temperature.
When shivering does occur, these active warming techniques are often the first line of treatment. In more persistent or severe cases, medications may be used to reduce shivering. These can include drugs like meperidine, tramadol, clonidine, ketamine, or even acetaminophen, which work by influencing the body’s temperature regulation thresholds. Healthcare providers in the recovery room continuously monitor the patient’s temperature, oxygen levels, and overall condition to provide appropriate care.
When Shivering is a Concern
While post-anesthesia shivering is a common and temporary side effect, there are situations where it might indicate a more serious issue. Shivering itself is not dangerous, but it does increase the body’s demand for oxygen, which can be a concern for patients with pre-existing heart or lung conditions. For this reason, patients experiencing shivering may be given supplemental oxygen.
It is important to inform medical staff if shivering is severe, persistent, or accompanied by other symptoms. Concerns might arise if shivering continues for an unusually long period, intensifies despite warming measures, or is combined with symptoms such as difficulty breathing, chest pain, confusion, or signs of infection like fever. Although rare, these accompanying symptoms could suggest an underlying complication, and prompt medical evaluation ensures appropriate intervention.