Postanaesthetic shivering in children

Clinical considerations in the use of forced-air warming blankets during orthognathic surgery to avoid postanesthetic shivering

Background

During head and neck surgery including orthognathic surgery, mild intraoperative hypothermia occurs frequently. Hypothermia is associated with postanesthetic shivering, which may increase the risk of other postoperative complications. To improve intraoperative thermoregulation, devices such as forced-air warming blankets can be applied. This study aimed to evaluate the effect of supplemental forced-air warming blankets in preventing postanesthetic shivering.

Methods

This retrospective study included 113 patients who underwent orthognathic surgery between March and September 2015. According to the active warming method utilized during surgery, patients were divided into two groups: Group W (n = 55), circulating-water mattress; and Group F (n = 58), circulating-water mattress and forced-air warming blanket. Surgical notes and anesthesia and recovery room records were evaluated.

Results

Initial axillary temperatures did not significantly differ between groups (Group W = 35.9 ± 0.7℃, Group F = 35.8 ± 0.6℃). However, at the end of surgery, the temperatures in Group W were significantly lower than those in Group F (35.2 ± 0.5℃ and 36.2 ± 0.5℃, respectively, P = 0.04). The average body temperatures in Groups W and F were, respectively, 35.9 ± 0.5℃ and 36.2 ± 0.5℃ (P = 0.0001). In Group W, 24 patients (43.6%) experienced postanesthetic shivering, while in Group F, only 12 (20.7%) patients required treatment for postanesthetic shivering (P = 0.009, odds ratio = 0.333, 95% confidence interval: 0.147–0.772).

Conclusions

Additional use of forced-air warming blankets in orthognathic surgery was superior in maintaining normothermia and reduced the incidence of postanesthetic shivering.

Dexmedetomidine for the treatment of postanesthesia shivering in children

BACKGROUND

Shivering is a common postanesthesia adverse event with multiple etiologies and multiple suggested prophylactic and abortive treatment regimens. Dexmedetomidine, a centrally acting alpha(2)-adrenergic agonist, has been used as a sedative agent and is known to reduce the shivering threshold. We hypothesized that children with postanesthesia shivering would reduce shivering behavior following a single bolus dose of dexmedetomidine.

METHODS

Dexmedetomidine was administered in a prospective, open-label fashion. The anesthesia management was uniform consisting of maintenance inhaled anesthesia (sevoflurane) and the intraoperative administration of fentanyl (1-2 microg.kg(-1)) plus a regional anesthetic technique (either a neuraxial or peripheral block) for postoperative analgesia. Criteria for treatment included: (i) shivering, (ii) successful extubation, and (iii) no other complaint/indication of pain. All children who met the criteria were treated with a single intravenous bolus dose of dexmedetomidine (0.5 microg.kg(-1)) over 3-5 min. Following the completion of drug administration, shivering activity was recorded every minute (up to 10 min) with any adverse effects or complaints. The efficacy of shivering reduction at 5 min in this cohort is compared with previous reports from the literature of the efficacy of clonidine and meperidine.

RESULTS

Twenty-four children ranging in age from 7 to 16 years (11.5 +/- 2.5 years) were treated. All children had a cessation of shivering behavior within 5 min following the completion of dexmedetomidine administration. The onset of effect was 3.5 +/- 0.9 min. No adverse effects were observed. No shivering behavior recurred.

CONCLUSIONS

This study demonstrates the efficacy of dexmedetomidine in the treatment of postanesthesia shivering.

Independent risk factors for postoperative shivering

Postoperative shivering (PAS) is uncomfortable for patients and potentially risky. In this observational trial we sought to identify independent risk factors for PAS after general anesthesia. Potential risk factors for PAS were recorded in 1340 consecutive patients. Signs of shivering, peripheral and core temperature, and thermal comfort were recorded in the postanesthetic care unit. The data were split into an evaluation data set (n = 1000) and a validation data set (n = 340). The first was used to identify independent risk factors for PAS and to formulate a risk score using backward-elimination logistic regression analysis. The proposed model was subsequently tested for its discrimination and calibration properties using receiver operating characteristic (ROC)-curve analysis and linear correlation between the predicted and the actual incidences of PAS in the validation group. The incidence of PAS was 11.6%. There were three major risk factors: young age, endoprosthetic surgery, and core hypothermia, with age being the most important. The risk score derived from this analysis had a reasonable discriminating power, with an area under the ROC-curve of 0.69 (95% confidence interval, 0.60-0.78; P < 0.0001). Furthermore the equation of the calibration curve (y = 0.69x + 6; R2= 0.82; P < 0.05) indicated a good and statistically significant agreement between predicted and actual PAS incidence. Postoperative shivering can be predicted with acceptable accuracy using the four risk factors identified in the present study. The presented model may serve as a clinical tool to help clinicians to rationally administer prophylactic antishivering drugs.

Postoperative shivering in children and causative factors

BACKGROUND

The aim of this study is to investigate the incidence of shivering in children and to reveal the causative factors as well as any possible clinical implications.

METHODS

This study was conducted on 1507 children who underwent surgery under general anesthesia. The patients were admitted to the postanesthesia care unit after the operation and their body temperatures measured from the tympanic membrane. The type of operation, operative time, method of anesthesia induction, age, and number of cases in which caudal block had been used were recorded.

RESULTS

Of the 1507 children, 53 (3.5%) experienced shivering. The use of intravenous induction agents, age older than 6 years, and prolonged duration of surgery were associated with shivering. The type of the operation and gender had no effect. The frequency of shivering was lower in children who underwent caudal block with a statistical significance (P < 0.05).

CONCLUSIONS

The overall incidence of shivering in children is low (3.5%). Use of intravenous induction agents, age older than 6 years, and prolonged duration of surgery were associated with shivering; prophylaxis is not necessary in children, treatment is given only when shivering occurs.

Physiology and clinical relevance of induced hypothermia

Experimental evidence and clinical experience suggest that mild hypothermia protects numerous tissues from damage during ischemic insult. However, the extent to which hypothermia becomes a valued therapeutic option will depend on the clinician's ability to rapidly reduce core body temperature and safely maintain hypothermia. To date, general anesthesia is the best way to block autonomic defenses during induction of mild-to-moderate hypothermia; unfortunately, general anesthesia is not an option in most patients likely to benefit from therapeutic hypothermia. Induction of hypothermia in awake humans is complicated by both the technical difficulties related to thermal manipulation and the remarkable efficacy of thermoregulatory defenses, especially vasoconstriction and shivering. The most effective thermal manipulation devices are generally invasive and, therefore, more prone to complications than surface methods. In an effort to inhibit thermoregulation in awake humans, several agents have been tested either alone or in combination with each other. For example, the combination of meperidine and buspirone has already been applied to facilitate induction of hypothermia in human trials. However, pharmacological induction of thermoregulatory tolerance to cold without excessive sedation, respiratory depression, or other serious toxicity remains a major focus of current therapeutic hypothermia research.

Postoperative shivering in children: a review on pharmacologic prevention and treatment

Postoperative shivering consists of muscular tremor and rigidity. It is often associated with body heat loss, although hypothermia alone does not fully explain the occurrence of shivering. Shivering is self-limiting, never becomes chronic, and is rarely associated with major morbidity. However, it affects the comfort of the patients, and may sometimes lead to more serious complications. The efficacy of a great variety of pharmacologic interventions to prevent shivering and to treat established symptoms has been tested in randomized controlled trials. These can be gathered systematically; recommendations on prevention and treatment can then be based on the strongest evidence. Unfortunately all these trials have been performed in adults. Thus, recommendations for the control of postoperative shivering in children have to be extrapolated from adult data. In adults, a systematic review strongly suggests that simple measurements are efficacious for both prevention and treatment. For prevention, extrapolation of these adult data indicates that three children have to receive intravenous clonidine 1.5 micro g/kg during anesthesia for one not to shiver, when they would have done so had they not received clonidine. For this degree of efficacy, the expected incidence of shivering (baseline risk) has to be high (approximately 50%). For treatment, extrapolation from adult data indicates that less than two children need to receive intravenous meperidine (pethidine) 0.35 mg/kg, or clonidine 1.5 micro g/kg for one to stop shivering five minutes after drug administration, when they would not have done so had they not received one of these drugs. Since the treatment of established shivering is efficacious, simple, inexpensive, and relatively safe, and since prevention is only efficacious if the baseline risk is very high, we recommend the 'wait and see' strategy.

Postanaesthetic shivering: epidemiology, pathophysiology, and approaches to prevention and management

Along with nausea and vomiting, postanaesthetic shivering is one of the leading causes of discomfort for patients recovering from general anaesthesia. The distinguishing factor during electromyogram recordings between patients with postanaesthetic shivering and shivering in fully awake patients is the existence of clonus similar to that recorded in patients with spinal cord transection. Clonus coexists with the classic waxing and waning signals associated with cutaneous vasoconstriction (thermoregulatory shivering). The primary cause of postanaesthetic shivering is peroperative hypothermia, which sets in because of anaesthetic-induced inhibition of thermoregulation. However, shivering associated with cutaneous vasodilatation (non-thermoregulatory shivering) also occurs, one of the origins of which is postoperative pain. Apart from causing discomfort and aggravation of pain, postanaesthetic shivering increases metabolic demand proportionally to the solicited muscle mass and the cardiac capacity of the patient. No link has been demonstrated between the occurrence of shivering and an increase in cardiac morbidity, but it is preferable to avoid postanaesthetic shivering because it is oxygen draining. Prevention mainly entails preventing peroperative hypothermia by actively rewarming the patient. Postoperative skin surface rewarming is a rapid way of obtaining the threshold shivering temperature while raising the skin temperature and improving the comfort of the patient. However, it is less efficient than certain drugs such as meperidine, clonidine or tramadol, which act by reducing the shivering threshold temperature.

Atropine prevents midazolam-induced core hypothermia in elderly patients

STUDY OBJECTIVE

To test the hypothesis that core temperature is well preserved when atropine and midazolam are combined.

DESIGN

Randomized, blinded study.

SETTING

Department of Anesthesia, Yamanashi Medical University.

PATIENTS

40 elderly, ASA physical status I and II patients (aged more than 60 years).

INTERVENTIONS

Patients were randomly assigned (n = 10 per group) to premedication with: 1) saline control; 2) midazolam 0.05 mg/kg; 3) atropine 0.01 mg/kg; and 4) midazolam 0.05 mg/kg combined with atropine 0.01 mg/kg. All premedication was given on the ward at approximately 8:30 am, approximately 30 minutes before induction of anesthesia.

MEASUREMENTS AND MAIN RESULTS

Core temperatures were measured at the right tympanic membrane. Mean skin temperature was calculated as 0.3 x (T(chest) + T(arm)) + 0.2 x (T(thigh) + T(calf)). Fingertip perfusion was evaluated using forearm minus fingertip and calf minus toe, skin-surface temperature gradients. Temperatures were evaluated at the time of premedication and 30 minutes later, just before induction of anesthesia. Core temperature remained nearly constant in the control patients (0.1 +/- 0.2 degrees C; mean +/- SD), whereas it decreased significantly in the patients given midazolam alone (-0.3 +/- 0.1 degrees C). Atropine alone increased core temperature (0.3 +/- 0.2 degrees C), although the increase was not statistically significant. The combination of midazolam and atropine attenuated the hypothermia induced by midazolam alone (0.0 +/- 0.2 degrees C). Initial skin-temperature gradients exceeded 0 degrees C in all groups, indicating that the patients were vasoconstricted. The gradients were unchanged by premedication with saline or atropine. Midazolam significantly decreased the gradient (-1.8 +/- 1.1 degrees C), as did the combination of midazolam and atropine (-1.4 +/- 0.9 degrees C).

CONCLUSIONS

The thermoregulatory effects of benzodiazepine receptor agonist and cholinergic inhibitors oppose each other, and the combination leaves core temperature unchanged.

Neither nalbuphine nor atropine possess special antishivering activity

The special antishivering action of meperidine may be mediated by its kappa or anticholinergic actions. We therefore tested the hypotheses that nalbuphine or atropine decreases the shivering threshold more than the vasoconstriction threshold. Eight volunteers were each evaluated on four separate study days: 1) control (no drug), 2) small-dose nalbuphine (0.2 microg/mL), 3) large-dose nalbuphine (0.4 microg/mL), and 4) atropine (1-mg bolus and 0.5 mg/h). Body temperature was increased until the patient sweated and then decreased until the patient shivered. Nalbuphine produced concentration-dependent decreases (mean +/- SD) in the sweating (-2.5 +/- 1.7 degrees C. microg(-1). mL; r(2) = 0.75 +/- 0.25), vasoconstriction (-2.6 +/- 1.7 degrees C. microg(-1). mL; r(2) = 0.75 +/- 0.25), and shivering (-2.8 +/- 1.7 degrees C. microg(-1). mL; r(2) = 0.79 +/- 0.23) thresholds. Atropine significantly increased the thresholds for sweating (1.0 degrees C +/- 0.4 degrees C), vasoconstriction (0.9 degrees C +/- 0.3 degrees C), and shivering (0.7 degrees C +/- 0.3 degrees C). Nalbuphine reduced the vasoconstriction and shivering thresholds comparably. This differs markedly from meperidine, which impairs shivering twice as much as vasoconstriction. Atropine increased all thresholds and would thus be expected to facilitate shivering. Our results thus fail to support the theory that activation of kappa-opioid or central anticholinergic receptors contribute to meperidine's special antishivering action.

Postoperative shivering: aetiology and treatment

Most postanaesthetic shivering-like tremor is normal thermoregulatory shivering in response to core hypothermia. Therefore, shivering will be prevented by maintaining intraoperative normothermia. Other thermoregulatory-related shivering is caused by the release of cytokines by the surgical procedure. Non-thermoregulatory shivering, occurring in normothermic patients, is caused by other aetiologies such as postoperative pain. It is thus likely that adequate treatment of postoperative pain will ameliorate non-thermoregulatory tremor. In addition, the administration of antipyretic drugs reduces shivering in patients after cardiopulmonary bypass surgery.