Lower-Body Warming Mimics the Normal Epidural-Induced Reduction in the Shivering Threshold

Thermoregulation: A journey from physiology to computational models and the intensive care unit

Thermoregulation plays a vital role in homeostasis. Many species of animals as well as humans have evolved various physiological mechanisms for body temperature control, which are characteristically flexible and enable a fine-tuned spatial and temporal regulation of body temperature in different environmental conditions and circumstances. Human beings normally maintain a core body temperature at around 37°C, and maintenance of this relatively high temperature is critical for survival. Therefore, principles of thermoregulatory control have also important clinical implications. Infections can cause the body temperature to rise internally and several diseases can cause a dysfunction of thermoregulatory mechanisms. Moreover, the utilization of thermotherapies in treating various diseases has been known for thousands of years with a recent resurgence of interest. An increasing amount of research suggests that targeted temperature management is of paramount importance to patient outcomes in certain clinical scenarios. We provide a concise summary of the basic concepts of thermoregulation. Emphasis is given to the principles of thermoregulation in humans in basic pathological states and to targeted temperature management strategies in the clinical environment, with special attention on therapeutic hypothermia in postcardiac arrest patients. Finally, the discussion is focused on the potential offered by computational thermophysiological models for predicting thermal responses of patients in various clinical circumstances, for proposing new perspectives in the design of novel thermal therapies, and to optimize targeted temperature management strategies. This article is categorized under: Cardiovascular Diseases > Cardiovascular Diseases>Computational Models Cardiovascular Diseases > Cardiovascular Diseases>Environmental Factors Cardiovascular Diseases > Cardiovascular Diseases>Biomedical Engineering.

Postanaesthetic shivering - from pathophysiology to prevention

Postoperative shivering is a common complication of anaesthesia. Shivering is believed to increase oxygen consumption, increase the risk of hypoxemia, induce lactic acidosis, and catecholamine release. Therefore, it might increase the postoperative complications especially in high-risk patients. Moreover, shivering is one of the leading causes of discomfort for postsurgical patients. Shivering is usually triggered by hypothermia. However, it occurs even in normothermic patients during the perioperative period. The aetiology of shivering has been understood insufficiently. Another potential mechanism is pain and acute opioid withdrawal (especially with the use of short-acting narcotics). Besides that shivering is poorly understood, the gold standard for the treatment and prevention has not been defined yet. Perioperative hypothermia prevention is the first method to avoid shivering. Many therapeutic strategies for treating shivering exist and most are empiric. Unfortunately, the overall quality of the antishivering guidelines is low. Two main strategies are available: pharmacological and non-pharmacological antishivering methods. The combination of forced-air warming devices and intravenous meperidine is the most validated method. We also analysed different medications but final conclusion about the optimal antishivering medication is difficult to be drawn due to the lack of high-quality evidence. Nevertheless, control of PS is possible and clinically effective with simple pharmacological interventions combined with non pharmacological methods. However, to be consistent with the most up-to-date, evidence-based practice, future antishivering treatment protocols should optimize methodological rigor and transparency.

Perioperative thermoregulation and heat balance

Core body temperature is normally tightly regulated to within a few tenths of a degree. The major thermoregulatory defences in humans are sweating, arteriovenous shunt vasoconstriction, and shivering. The core temperature triggering each response defines its activation threshold. General anaesthetics greatly impair thermoregulation, synchronously reducing the thresholds for vasoconstriction and shivering. Neuraxial anaesthesia also impairs central thermoregulatory control, and prevents vasoconstriction and shivering in blocked areas. Consequently, unwarmed anaesthetised patients become hypothermic, typically by 1-2°C. Hypothermia results initially from an internal redistribution of body heat from the core to the periphery, followed by heat loss exceeding metabolic heat production. Complications of perioperative hypothermia include coagulopathy and increased transfusion requirement, surgical site infection, delayed drug metabolism, prolonged recovery, shivering, and thermal discomfort. Body temperature can be reliably measured in the oesophagus, nasopharynx, mouth, and bladder. The standard-of-care is to monitor core temperature and to maintain normothermia during general and neuraxial anaesthesia.

Effect of Intraoperative Phenylephrine Infusion on Redistribution Hypothermia During Cesarean Delivery Under Spinal Anesthesia

An observational clinical study to evaluate the effect of phenylephrine infusion on maternal temperatures during scheduled cesarean delivery under spinal anaesthesia was conducted in 40 ASA physical status II parturients. Following placement of spinal anesthesia, phenylephrine infusion was initiated at 40 μg/min and titrated to maintain mean arterial pressure within 20 percent of baseline. Maternal oral temperature, heart rate, and blood pressure were measured at baseline, spinal placement, every 10 minutes thereafter for 60 minutes. Phenylephrine dose received was documented every ten minutes. The range in maternal temperature change was 0.06-0.29°C. The lowest recorded temperature was 36.3°C. Decreased maternal temperature was associated with duration of anesthesia and cumulative phenylephrine dose in a univariate model (P<0.001 for all). The multivariable model showed an association between a greater decrease in maternal temperature with larger doses of phenylephrine being administered.

The effects of warm and cold intrathecal bupivacaine on shivering during delivery under spinal anesthesia

Background:

Shivering associated with neuraxial anesthesia is a common problem that is uncomfortable for patients; it is of unknown ethnology and has no definite treatment.

Purpose:

The purpose of this study was to compare the effects of warm intrathecal bupivacaine stored at 23°C and cold intrathecal bupivacaine stored at 4°C on shivering during delivery under spinal anesthesia.

Methods:

Seventy-eight parturient women scheduled for nonemergency cesarean delivery were enrolled in the study and separated into 2 groups. The standard group received 10 mg of heavy bupivacaine 0.5% stored at room temperature (23°C) plus 10 μg of fentanyl intrathecally (warm group), and the case group received 10 mg of heavy bupivacaine 0.5% stored at 4°C plus 10 μg of fentanyl intrathecally (cold group). Data collection, including sensory block level, blood pressure, core temperature, and shivering intensity, was first performed every minute for 10 min, then every 5 min for 35 min and, finally, every 10 min until the sensory level receded to L4.

Results:

There were no differences between the 2 groups in the amount of bleeding, pulse rate, oxygen saturation, neonatal Apgar, and incidence of vomiting. The incidence and intensity of shivering decreased in the warm group (P=0.002).

Conclusion:

Warming of solutions can reduce the incidence and intensity of shivering in parturient candidates for cesarean delivery under spinal anesthesia.

Effect of active warming on shivering during spinal anesthesia

BACKGROUND

Hypothermia is considered one of the reasons for intraoperative shivering. The purpose of this study is to assess whether active warming can prevent hypothermia and shivering in young adults under spinal anesthesia.

METHODS

Fifty male patients scheduled for an elective operation on lower extremity under spinal anesthesia were randomly assigned into the warming group (n = 25) and the control group (n = 25). The active warming was performed using a forced air-warming device, a warmed blanket and warmed fluid. Axillary and tympanic temperatures, shivering degree, thermal discomfort, and anesthetic level were checked every 10 minutes after intrathecal injection of local anesthetics.

RESULTS

Patients' characteristics and anesthetic levels were comparable between the groups. Axillary and tympanic temperatures were maintained higher in the warming group than the control group 10 minutes and 20 minutes after intrathecal injection respectively. The lowest temperature in operating room was higher in the warming group (36.3 +/- 0.5degrees C) compared with the control group (35.7 +/- 0.5degrees C) (P < 0.05). Incidences of intraoperative shivering and thermal discomfort were lower in the warming group.

CONCLUSIONS

We conclude that intraoperative active warming can prevent hypothermia and shivering during spinal anesthesia.