Propofol and postanaesthetic shivering

Control of Shivering During Targeted Temperature Management

Targeted temperature management (TTM) is used frequently in patients with a variety of diseases, especially those who have experienced brain injury and/or cardiac arrest. Shivering is one of the main adverse effects of TTM that can often limit its implementation and efficacy. Shivering is the body's natural response to hypothermia and its deleterious effects can negate the benefits of TTM. The purpose of this article is to provide an overview of TTM strategies and shivering management.

Experience of adverse events with cerebral propofol testing in patients with drug resistant epilepsy

The aim of this study was to assess the type and frequency of adverse events during the Wada test conducted with propofol as an anaesthetic agent. In total, 122 patients with temporal lobe epilepsy underwent the Wada test with propofol between 2006 and 2016 as part of presurgical evaluation at the Department of Neurosurgery of the Medical University of Warsaw. The Wada test was conducted bilaterally on 118 patients (236 cases). In four cases, due to complications, the test was conducted only unilaterally, which resulted in a total of 240 cases. Those cases were further analysed for the presence of adverse events. In all cases, intracranial circulation angiography (via the transfemoral approach) was performed before memory and language testing. Of the 122 patients, adverse events were observed in 75 patients (61.4%). Serious complications were notably rare and observed only in two patients (1.6%): one patient had a carotid artery dissection, and the other had a pseudoaneurysm at the puncture site. Mild adverse events (e.g., shivers or pain of the eye) were highly common - we observed them in 71 patients (58%), but they were short-term and well-tolerated by the subjects. Two patients (1.6%) had a seizure during the Wada test. Most of the adverse events occurring during the Wada test with propofol were mild and short-lived. Considering a small risk of serious damage to health, this procedure can be perceived as a good method for assessing language and memory in a fraction of the epilepsy surgery candidates.

Parecoxib for the prevention of shivering after general anesthesia

BACKGROUND

Shivering is the most common complication during the recovery period after general anesthesia, and there is no clear consensus about the best strategy for its prophylactic. The aim of the study was to evaluate the efficacy of parecoxib in prevention of postoperative shivering.

METHODS

Eighty patients with American Society of Anesthesiologists physical status I-II, who were scheduled for minor urological surgeries under general anesthesia, were randomly assigned to two groups (n = 40 in each group): group P received 40 mg of parecoxib by intravenous bolus injection and group S received the same volume of normal saline in the same way just after the induction of anesthesia. Hemodynamic parameters and body temperatures including tympanic and axillary temperature were monitored. The occurrence of shivering and pain intensity score were recorded during the recovery period.

RESULTS

Parecoxib significantly reduced the incidence and severity of shivering in comparison with the placebo. Postoperative shivering was observed in 22 patients in group S (55%), compared with nine in group P (22.5%) (P = 0.003). In addition, pain intensity scores were lower in group P during recovery period; consequently, less rescue analgesics were required in group P when compared with group S (P = 0.001). Regarding the body temperature, it was found that core temperature decreased but peripheral temperature increased significantly in both groups. There was no significant difference between groups in all time intervals.

CONCLUSIONS

Prophylactic administration of parecoxib produces dual effects on antishivering and postoperative analgesia. This implies that cyclooxygenase 2-prostaglandin E2 pathways may be involved in the regulation of shivering.

Postoperative Management of Shivering: A Comparison of Pethidine vs. Ketamine

Background:

One of the unpleasant side effects of general anesthesia is shivering in the process of recovery. It is an involuntary oscillatory mechanical movement that can be classified as clonic movements. These movements can affect one or several groups of skeletal muscles beginning from 5 to 30 minutes after the discontinuation of anesthesia.

Objectives:

We aimed to study ketamine’s effect on shivering after operation compared to pethidine as a way for treatment of postoperative shivering.

Patients and Methods:

In this study, 60 patients who underwent ENT surgery with general anesthesia and had shivering during recovery were randomly divided into two groups of 30 patients each receiving ketamine (0.2 mg/kg IV) and pethidine (0.5 mg/kg).

Results:

There was no statistically significant difference between the shivering intensity in both groups. Only regarding the shivering in the first minute after entering the recovery room, there was an obvious difference between ketamine and pethidine groups which was again not statistically significant (P = 0.07).

Conclusions:

The results of this study showed that ketamine and pethidine are both equally effective in the reduction of postoperative shivering.

Progress in shivering control

Hypothermia is a potent neuroprotectant and induced hypothermia holds great promise as a therapy for acute neuronal injury. Thermoregulatory responses, most notably shivering, present major obstacles to therapeutic temperature management. A review of thermoregulatory physiology and strategies aimed at controlling physiologic responses to hypothermia is presented.

Remifentanil-propofol in vertebral disk operations: hemodynamics and recovery versus desflurane-n(2)o inhalation anesthesia

The purpose of this study was to ascertain whether total intravenous anesthesia (TIVA) with propofol and remifentanil differs from inhalational anesthesia with desflurane and nitrous oxide in terms of hemodynamics, recovery profile, and postoperative analgesic demand in patients undergoing elective microsurgical vertebral disk resection. A total of 60 patients were randomly assigned to receive TIVA with propofol and remifentanil or inhalational anesthesia with desflurane and nitrous oxide. The TIVA group (n=30) then received 50%/50% N(2)O/O(2). A constant infusion of remifentanil was provided at 0.125 microg/kg/min accompanied by propofol at 10 mg/kg/h in the first 10 min, 6 mg/kg/h in the second 10 min, then 4 mg/kg/h. The desflurane group (n=30) received 50%/50% N(2)O/O(2), with 5% desflurane after intubation and 6% before incision; desflurane was administered in a minimum alveolar concentration 1 fashion during the operation. Hemodynamic, O(2) saturation, and end-tidal CO(2) data were recorded before induction, after intubation, after prone positioning, 5, 10, 15, 20, and 30 min into the operation, and at 15-min intervals thereafter until the end of the operation. Details on perioperative bradycardia, hypotension or hypertension, spontaneous breathing, extubation, eye opening, recovery time of ability to give name and date of birth, postoperative nausea and vomiting, shivering, agitation, and hypoxia were recorded. Patients anesthetized with desflurane responded to skin incision with increasing blood pressure and tachycardia; however, no other hemodynamic differences were noted between the 2 groups. In the TIVA group, recovery times were shorter for spontaneous ventilation (2.33-3.53 min), extubation (3.13-3.88 min), eye opening (4.06-6.23 min), and being able to give name and date of birth (5.4-7.9 min) compared with times in the desflurane group (P<.05). In the TIVA group, more postoperative shivering (16.7% of patients) and greater analgesic demand were seen than in the desflurane group. Although nausea and vomiting were more common in the desflurane group, no difference in bronchospasm was reported. In the TIVA group, a shorter recovery period and a greater demand for postoperative analgesia were seen. Because of the lack of residual analgesic effects, postoperative analgesic treatment should be initiated immediately in patients undergoing TIVA.

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.

Dolasetron for preventing postanesthetic shivering

We designed this study to assess the efficacy of dolasetron compared with clonidine and placebo in prophylaxis of postanesthetic shivering. We included 90 patients undergoing elective abdominal or urologic surgery. The patients were randomly assigned to one three groups (each group n = 30) using a double-blinded study protocol: Group A received 12.5 mg dolasetron, Group B 3 microg/kg clonidine, and Group C saline 0.9% as placebo. The medication was given after the induction of anesthesia. Postanesthetic shivering was judged by using a five-point scale. In the Clonidine group, 86.6% showed no shivering, whereas in the Dolasetron and Placebo groups, only 63.3% and 66.6%, respectively, were symptom free. Only clonidine, but not dolasetron, significantly reduced the incidence and the severity of shivering. We conclude that clonidine is effective in preventing shivering when given before surgery, whereas dolasetron, at the dose used, is not effective.

IMPLICATIONS

Shivering, an irregular muscular fasciculation lasting longer than 15 s, is a common complication secondary to general anesthesia. We compared dolasetron with clonidine (an established antishivering drug) in the prevention of postanesthetic shivering. Dolasetron 12.5 mg was not effective.

Urapidil does not prevent postanesthetic shivering: a dose-ranging study

PURPOSE

To investigate the effect of 0.2 mg x kg(-1), 0.3 mg x kg(-1) and 0.4 mg x kg(-1) urapidil on the incidence and severity of postanesthetic shivering.

METHODS

One hundred and fifty patients (ASA I-III) scheduled for elective abdominal, urologic or orthopedic surgery under standardized general anesthesia were randomly allocated to one of five groups (each group n=30) using a double-blind protocol: group A received 0.2 mg x kg(-1) urapidil, group B: 0.3 mg x kg(-1) urapidil, group C: 0.4 mg x kg(-1) urapidil, group D: 3 microg x kg(-1) clonidine (positive control group), and group E: saline 0.9% as placebo (negative control group). Postanesthetic shivering was scored using a five-point scale.

RESULTS

Twelve patients of group A, 11 of group B, nine of group C, three of group D and 14 of group E showed signs of postanesthetic shivering. Postanesthetic shivering was significantly decreased in the clonidine group compared to the three urapidil groups and the placebo group. Significantly less patients treated with clonidine needed anti-shivering therapy. There were no significant differences between the urapidil and placebo groups. Therapeutic interventions for hemodynamic effects were not required in any group. Time to extubation, but not time to discharge, was prolonged in the clonidine group.

CONCLUSION

Urapidil showed no beneficial effect on shivering in any of the doses evaluated, whereas prophylactic administration of clonidine was effective in preventing postanesthetic shivering.

Tramadol for postoperative shivering: a double-blind comparison with pethidine

In most operating and recovery rooms, shivering is controlled by the use of humidifiers, warming blankets, and inhalation of humidified heated oxygen. However, pharmacological control is an effective alternate treatment modality. This randomized, double-blind trial, conducted in 30 ASA Grade 1 or 2 patients, was designed to explore the efficacy of tramadol and pethidine in the treatment of post-anaesthetic shivering. Tramadol is an inhibitor of the re-uptake of serotonin (5-hydroxytryptamine) and norepinephrine in the spinal cord. This facilitates 5-hydroxytryptamine release, which influences thermoregulatory control. We compared the efficacy of tramadol with that of pethidine, presently a widely used drug for the control of shivering. Patients received either tramadol 1 mg/kg or pethidine 0.5 mg/kg intravenously and the grade of shivering, pulse rate, blood pressure and respiratory rate were observed every 10 minutes after injection for one hour Shivering was significantly more likely to have ceased in the tramadol group (12 of 15 versus 4 of 15 cases, P<0.05) at 10 minutes after drug administration and this control was better sustained. No patients receiving tramadol had a recurrence of shivering. It is concluded that intravenous tramadol 1 mg/kg is more effective for the treatment of postoperative shivering than pethidine 0.5 mg/kg.

A comparison of urapidil, clonidine, meperidine and placebo in preventing postanesthetic shivering

This placebo-controlled study was performed to evaluate the efficacy of urapidil compared with clonidine and meperidine in preventing postanesthetic shivering, which is common after anesthesia administration and may be very distressing. We studied 120 patients undergoing elective abdominal or orthopedic surgery under standardized general anesthesia. After surgery, patients were randomly assigned to one of four groups (each group n = 30) using a double-blinded protocol: Group A received 0.2 mg/kg urapidil; Group B, 3 microg/kg clonidine; Group C, 0.4 mg/kg meperidine; and Group D, saline 0.9% as placebo. Postanesthetic shivering was scored by using a five-point scale. Clonidine and meperidine significantly reduced the incidence and the severity of shivering in comparison with placebo, whereas there were no significant differences between the urapidil and placebo groups. Both clonidine and meperidine caused a significantly prolonged emergence time (13.4 +/- 5.8 and 13. 3 +/- 5.0 min, respectively) compared with placebo (10.4 +/- 5.3 min) and urapidil (11.4 +/- 2.9 min). We confirmed that both clonidine and meperidine are effective in preventing postanesthetic shivering, whereas urapidil, in our setting and dosage, was not effective. Patients who received clonidine or meperidine had a prolonged emergence time. In the dosage used, urapidil seems to be unable to prevent postanesthetic shivering.

IMPLICATIONS

Shivering (irregular muscle activity) is common after surgery and anesthesia. This study compared urapidil (an antihypertensive drug) as a prophylaxis with two established antishivering drugs (meperidine and clonidine) and placebo. In the dosage used, we were unable to show a significant benefit of urapidil.

A multicenter comparison of isoflurane and propofol as adjuncts to remifentanil-based anesthesia

STUDY OBJECTIVE

To compare recovery, hemodynamics, and side effects of remifentanil-based anesthesia with hypnotic concentrations of isoflurane or propofol.

DESIGN

Multicenter, prospective, randomized, two-group study.

SETTING

15 university and 5 municipal hospitals.

PATIENTS

249 ASA physical status I, II, and III adult patients scheduled for elective gynecological laparoscopy, varicose vein, or arthroscopic surgery of at least 30 minutes' duration.

INTERVENTIONS

Anesthesia was induced in the same manner in both groups: remifentanil-bolus (1 microg/kg), start of remifentanil-infusion (0. 5 microg/kg/min), followed by propofol as needed for induction. Five minutes after intubation, remifentanil was reduced to 0.25 microg/kg/min, and it was combined with either a propofol-infusion (0.1 mg/kg/min) or with isoflurane (0.6 vol% end-tidal) in O(2)/air. Adverse hemodynamic responses of heart rate and systolic blood pressure were recorded and treated according to a predefined protocol. With termination of surgery, anesthetic delivery was discontinued simultaneously without tapering, and recovery times were recorded.

MEASUREMENTS AND MAIN RESULTS

No significant differences were observed between the remifentanil-isoflurane or remifentanil-propofol treatment regimens. Recovery times (means +/- SD) were similar for spontaneous ventilation (5.8 +/- 3.2 min vs. 6. 3 +/- 3.7 min), extubation (7.6 +/- 3.5 vs. 8.5 +/- 4.2 min), eye opening (6.8 +/- 3.2 vs. 7.5 +/- 3.8 min), and arrival to the postanesthesia care unit (16.5 +/- 7.0 vs.18.0 +/- 7.2 min). There were no significant differences in adverse hemodynamic responses, postoperative shivering, nausea, or vomiting between the groups.

CONCLUSIONS

Emergence after remifentanil-based anesthesia with 0.6 vol% of isoflurane is at least as rapid as with 0.1 mg/kg/min propofol. Both isoflurane and propofol are suitable adjuncts to remifentanil, and the applied dosages are clinically equivalent with respect to emergence and recovery. Therefore, both combinations should be appropriate, particularly in settings in which rapid recovery from anesthesia is desirable, such as fast tracking and/or ambulatory surgery.

Metabolic and hemodynamic changes during recovery and tracheal extubation in neurosurgical patients: immediate versus delayed recovery

Delayed recovery has been advocated to limit the postoperative stress linked to awakening from anesthesia, but data on this subject are lacking. In this study, we measured oxygen consumption (V(O2)) and plasma catecholamine concentrations as markers of postoperative stress. We tested the hypothesis that delayed recovery and extubation would attenuate metabolic changes after intracranial surgery. Thirty patients were included in a prospective, open study and were randomized into two groups. In Group I, the patients were tracheally extubated as soon as possible after surgery. In Group II, the patients were sedated with propofol for 2 h after surgery. V(O2), catecholamine concentration, mean arterial pressure (MAP), and heart rate (HR) were measured during anesthesia, at extubation, and 30 min after extubation. V(O2) and noradrenaline on extubation and mean V(O2) during recovery were significantly higher in Group II than in Group I (V(O2) for Group I: preextubation 215 +/- 46 mL/min, recovery 198 +/- 38 mL/min; for Group II: preextubation 320 +/- 75 mL/min, recovery 268 +/- 49 mL/min; noradrenaline on extubation for Group I: 207 +/- 76 pg/mL, for Group II: 374 +/- 236 pg/ mL). Extubation induced a significant increase in MAP. MAP, HR, and adrenaline values were not statistically different between groups. In conclusion, delayed recovery after neurosurgery cannot be recommended as a mechanism of limiting the metabolic and hemodynamic consequences from emergence from general anesthesia.

IMPLICATIONS

In this study, we tested the hypothesis that delayed recovery after neurosurgery would attenuate the consequences of recovery from general anesthesia. As markers of stress, oxygen consumption and noradrenaline blood levels were higher after delayed versus early recovery. Thus, delayed recovery cannot be recommended as a mechanism of limiting the metabolic and hemodynamic consequences from emergence after neurosurgery.

Effect of low-dose propofol infusion on total-body oxygen consumption after coronary artery surgery

OBJECTIVE

To investigate the effect of low-dose propofol infusion on total-body oxygen consumption (VO2) after coronary artery bypass grafting (CABG) surgery.

DESIGN

A prospective, randomized, placebo-controlled, double-blind study.

SETTING

Cardiovascular intensive care unit in a university hospital.

PARTICIPANTS

Thirty patients after elective, uncomplicated CABG surgery.

INTERVENTION

Patients were administered a continuous infusion of propofol with a fixed rate of 1 mg/kg/h (n = 15) or placebo (n = 15) during the spontaneous rewarming period of approximately 5 hours after surgery. A light level of sedation (Ramsay sedation score > or =2) was maintained by administering small doses of diazepam, 0.1 mg/kg, as required. Morphine, 0.05 mg/kg, was administered for analgesia as required.

MEASUREMENTS AND MAIN RESULTS

Total-body VO2 was measured by indirect calorimetry. In addition, shivering (on a five-grade scale), hemodynamics, and plasma catecholamine and serum cortisol concentrations were measured. Diazepam, 5.6+/-7.4 mg (mean +/- standard deviation), was administered to the patients receiving propofol, and 16.1+/-12.2 mg was administered to the patients receiving placebo (p < 0.05). There was no difference in the dose of morphine between the groups (3.2+/-3.9 v 4.2+/-5.5 mg in the propofol and placebo groups, respectively). At any time during the study, VO2 was not different between the groups. VO2 increased from 130+/-29 to 172+/-29 mL/min/m2 in the propofol group and from 118+/-24 to 167+/-27 mL/min/m2 in the placebo group. Mean arterial pressure and heart rate were lower in the propofol group (p < 0.05). Stress hormone levels did not differ between the groups.

CONCLUSION

Low-dose propofol infusion and additional diazepam as required does not decrease total-body VO2 compared with a pure diazepam bolus-dose technique when administered for light sedation during the immediate recovery period after CABG surgery.

A comparison among nalbuphine, meperidine, and placebo for treating postanesthetic shivering

Postanesthetic shivering (PS) is distressing for patients and may induce a variety of complications. In this prospective, double-blinded, randomized study, we evaluated the value of nalbuphine, compared with meperidine and saline, for treating PS. Ninety adult patients were included in the study. Group 1 (n = 30) received i.v. nalbuphine 0.08 mg/kg, Group 2 (n = 30) received i.v. meperidine 0.4 mg/kg, and Group 3 (n = 30) received i.v. saline. Treatment that stopped shivering was considered to have been successful. The results demonstrated that, 5 min after treatment, both nalbuphine and meperidine provided a rapid and potent anti-shivering effect on PS, with high response rates of 80% and 83%, compared with those of saline (0%) (P < 0.01). Thirty minutes after injection, the response rates of nalbuphine and meperidine were 90% and 93%, respectively, compared with 17% in the saline group (P < 0.01). The differences between nalbuphine and meperidine were not significant. We conclude that nalbuphine may be an alternative to meperidine for treating PS.

IMPLICATIONS

We evaluated nalbuphine versus meperidine and saline for treating postanesthetic shivering. Our results demonstrate that both nalbuphine and meperidine provide a similar rapid and potent anti-shivering effect. Nalbuphine may be an alternative to meperidine for treating postanesthetic shivering.

Propofol-based versus fentanyl-isoflurane-based anesthesia for cardiac surgery

OBJECTIVE

To evaluate drug costs, time of mechanical ventilation, complications, and hospital length of stay comparing propofol-based with fentanyl-isoflurane-based anesthesia.

DESIGN

A prospective, randomized study.

SETTING

A university-affiliated, tertiary care community hospital.

PARTICIPANTS

Seventy patients undergoing primary coronary artery bypass surgery.

INTERVENTIONS

Patients were randomized to either a low-dose fentanyl-isoflurane or a lower-dose fentanyl-isoflurane anesthetic supplemented with a continuous infusion of propofol.

MEASUREMENTS AND MAIN RESULTS

Fentanyl-isoflurane anesthesia was significantly less expensive ($50.03+/-$27.26 v $121.69+/-$31.40) for anesthesia drugs and ($58.08+/-$27.39 v $129.91+/-$31.52) for total drug costs. There was also a trend for patients in the fentanyl-isoflurane group to be extubated slightly sooner (388+/-202 v 449+/-252 min) and go home sooner (5.1+/-1.8 v 6.0+/-3.0 days).

CONCLUSION

Fentanyl-isoflurane provides an inexpensive anesthetic that permits as prompt an extubation as propofol, thus conserving resources for other patients.

Late intraoperative clonidine administration prevents postanesthetic shivering after total intravenous or volatile anesthesia

Postoperative administration of clonidine is an effective treatment for shivering. However, the ability of this drug to stop postanesthetic shivering when administered intraoperatively remains controversial. Furthermore, the relative efficacy of clonidine during isoflurane and propofol anesthesia remains unknown. We therefore evaluated the incidence of postanesthetic shivering in patients given clonidine during nitrous oxide/isoflurane or propofol anesthesia. Because clonidine is an analgesic, we also evaluated postoperative pain and analgesic requirements. We studied 60 patients undergoing elective ear or nose surgery. General anesthesia was induced with 2.0 mg/kg propofol, 1.5 micrograms/kg fentanyl, and 0.1 mg/kg vecuronium. General anesthesia was maintained with isoflurane and 70% nitrous oxide in one group of patients; in the other, a continuous infusion of propofol (8 mg.kg-1.h-1) was administered (without nitrous oxide). Five minutes before tracheal extubation, patients in each group were randomly assigned to receive saline, placebo, or 3 micrograms/kg clonidine intravenously. Postanesthetic shivering was evaluated by a blind investigator. Postoperative pain was assessed using a visual analog scale. Postoperative shivering was observed in 53% of the patients given isoflurane without clonidine and in 13% of the patients given propofol without clonidine. No patient given clonidine shivered. Clonidine administration significantly reduced postoperative pain. The incidence of postanesthetic shivering was significantly less after propofol anesthesia than after isoflurane/nitrous oxide anesthesia. However, a late intraoperative bolus administration of 3 micrograms/kg clonidine prevents postoperative shivering in patients given either type of anesthesia.