Shivering is a frequent, and occasionally distressing, complication in the postoperative period . Apart from the discomfort, postanaesthetic shivering may increase the risk of complications such as increased intraocular pressure, pain in the incision site and adverse cardiovascular events in patients with coronary artery disease due to increased oxygen consumption [2-5]. The incidence of postanaesthetic shivering described in former studies varies between 6.3 and 66% . Many drugs have been used to prevent and control postanaesthetic shivering, including meperidine, clonidine, urapidil, nalbuphine, dexamethasone [6-8] and many others but the ideal drug has still not been found.
Central adrenergic receptors appear to modulate postanaesthetic shivering. Dexmedetomidine is an α2-agonist that decreases the vasoconstriction and shivering thresholds and with meperidine additively reduces the shivering threshold in healthy volunteers [9,10].
To date, no study has been performed to show that the prophylactic administration of dexmedetomidine prevents postanaesthetic shivering after major surgery. This placebo-controlled study was performed to evaluate the efficacy of dexmedetomidine compared with meperidine and placebo in preventing postanaesthetic shivering.
After obtaining approval from the local Ethics Committee and informed consent from the patients, we studied 120 patients (ASA I-II), aged 18-50 yr, scheduled for elective abdominal or orthopaedic surgery of about 1-3 h duration. None was obese (body mass index, BMI > 27), febrile, taking vasoactive, antidepressant or analgesic drugs or had a history of cardiovascular, respiratory, endocrine or neurological disease. Pregnancy was an exclusion criterion.
In all groups, general anaesthesia was induced with thiopental (5 mg kg−1) and fentanyl (1.5 μg kg−1). Atracurium (0.5 mg kg−1) was given to facilitate orotracheal intubation and general anaesthesia was maintained with 60% nitrous oxide in oxygen and sevoflurane (2.0 ± 0.5% end-tidal concentration). Mechanical ventilation was adjusted to maintain end-tidal carbon dioxide tension at 30-35 mmHg (Normocap®; Datex, Helsinki, Finland) using a fresh gas flow of 6 L min−1. The patients were covered with surgical drapes during anaesthesia but were not actively heated. Supplemental doses of atracurium were administered at the discretion of the anaesthesiologist.
At the time of wound closure, patients were randomly assigned to one of three groups (each group n = 40): Group D received 1 μg kg−1 dexmedetomidine i.v.; Group M received 0.5 mg kg−1 meperidine i.v. and the placebo group (Group P) received saline 0.9% i.v. Before surgery, after intubation, 5, 15, 30, 60 and 90 min during surgery, before drug administration, after drug administration, end of anaesthesia, after extubation, in postanaesthetic care unit (PACU) 0, 30 and 60 min, tympanic temperatures (Braun, IRT 3020, Type = 6012; ThermoScan, Kronberg, Germany) were measured. Operation room and PACU temperatures were recorded.
At the end of surgery, neuromuscular blockade was reversed with neostigmine 0.04 mg kg−1 i.v. and atropine 0.02 mg kg−1 i.v. and the trachea was extubated. Extubation time (from termination of sevoflurane application until extubation), duration of anaesthesia and duration of surgery were noted.
Awakening time was assessed by the patients' response to verbal commands (‘open your eyes and lift your arms’). Prompt responses were graded as ‘awake’ and the time from extubation was recorded. Orientation was assessed by the patients' response to questions regarding time, place and person, and the time from extubation was recorded. In the PACU, patients received standard postoperative management, including oxygen administration via a nasal cannula (3 L min−1) and a cotton blanket. Postanaesthetic recovery was scored according to the Aldrete scoring system .
Postanaesthetic shivering, pain and sedation scores were recorded every 10 min during recovery. Postanaesthetic shivering was graded as 0 = no shivering, 1 = mild fasciculations of face or neck or interference in the electrocardiogram, 2 = visible tremor in more than one muscle group, 3 = gross muscular activity involving the entire body. Postanaesthetic pain was graded by a verbal rate scale with 0 = no pain, 1 = slight pain, 2 = moderate pain, 3 = severe pain, 4 = very severe pain. Postanaesthetic sedation was graded as 1 = alert, 2 = alert but drowsy, 3 = responds to voice, 4 = responds to gentle tactile stimulation, 5 = responds to vigorous tactile stimulation, 6 = unarousable.
Patients were questioned for postoperative nausea, vomiting and for the occurrence of headache, dizziness, sweating or other discomfort. Postoperative analgesic and antiemetic requirements were recorded during the recovery period. Any patient with a shivering score of 2 or more was given 25 mg of i.v. meperidine as a rescue drug and no more data were recorded. Any patient with a pain score 2 or more was given an analgesic drug in the PACU.
Parametric data were analysed by using one-way analysis of variance. t-test was used to analyse differences among the groups. Non-parametric data were analysed by using the Kruskal-Wallis test. U-test was used to analyse differences among the groups. P values <0.05 were considered significant.
Patient characteristics, duration of surgery, duration of anaesthesia, time in PACU, operation and PACU room temperatures were similar in the three groups (P > 0.05, Table 1). Extubation, awakening and orientation times in the three groups are shown in Table 2.
Postanaesthetic shivering was seen in 22 patients in the placebo group (55%), four in the meperidine group (10%) and six in the dexmedetomidine group (15%). Dexmedetomidine and meperidine significantly reduced the incidence of shivering compared with placebo (P < 0.05) but there was no significant difference between the dexmedetomidine and meperidine groups (P > 0.05, Table 3).
Sedation scores were significantly higher in the dexmedetomidine group than in the meperidine and placebo groups, and were higher in the meperidine group than in the placebo group for 20 min in PACU (P < 0.05, Table 4). The groups did not differ significantly with regard to verbal pain scores (P > 0.05).
During the first 40 min in the recovery room, the Aldrete scores were significantly lower in the dexmedetomidine treated patients than in those of the other two groups (P < 0.05, Table 5).
Tympanic temperatures did not differ between the groups, but they were lower than baseline from 15 min after intubation until the end of the study period (P < 0.05, Table 6).
We found that 1 μg kg−1 dexmedetomidine reduced the incidence and the severity of shivering significantly compared with the placebo group.
Several hypotheses have been advanced to explain the occurrence of postanaesthetic shivering and these include perioperative hypothermia. Mild perioperative hypothermia does not necessarily occur before the appearance of postanaesthetic shivering but it encourages it. There are two types of postanaesthetic shivering. The first corresponds to thermoregulatory shivering that is associated with cutaneous vasoconstriction and which is the physiological response to the hypothermia developed during the perioperative period. The second corresponds to shivering associated with cutaneous vasodilatation or non-thermoregulatory shivering . In the study of Horn and colleagues , shivering was observed in 27% of the patients who were normothermic; 55% of this spontaneous muscular activity occurred in vasodilated patients. In the present study there were no significant differences among groups in tympanic temperature which might affect the preventing effects of the study drugs on shivering.
Postoperative surgical pain facilitates non-thermoregulatory shivering . In our study, there were no significant differences among the three groups in pain which was evaluated with verbal rate scaling. This is because that all patients in placebo group who had pain scores 2 or more received an analgesic drug for pain management in PACU.
Wrench and colleagues  reported that 0.35 mg kg−1 of meperidine is the minimum dose required to effectively treat postanaesthetic shivering. Horn and colleagues  used 0.5 mg kg−1 of meperidine to prevent postanaesthetic shivering prevention and no shivering was observed in their patients. The meperidine dose of 0.5 mg kg−1 used in our study is over the minimum dose required to treat postanaesthetic shivering.
Dexmedetomidine, the pharmacologically active dextro isomer of medetomidine, is a potent α2-adrenoceptor agonist with an eight times higher affinity for the α2-adrenoceptor than clonidine. It has shown sedative, analgesic and anxiolytic effects after i.v. administration in healthy volunteers or postsurgical patients in the intensive care unit . Intramuscular dexmedetomidine for premedication decreases the incidence of postoperative shivering , but the primary aim of this study was to compare dexmedetomidine and midazolam for premedication. The incidence of postoperative shivering was also decreased in patients given dexmedetomidine before and during coronary artery bypass grafting, but this was only a secondary observation .
In conclusion, the late intraoperative i.v. administration of dexmedetomidine (1 μg kg−1) prevents postanaesthetic shivering as does meperidine (0.5 mg kg−1), in our setting. However, the sedative effects of dexmedetomidine prolong the initial awakening and orientation times in comparison with meperidine and placebo.
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Keywords:© 2006 European Society of Anaesthesiology
ANAESTHESIA RECOVERY PERIOD; complications; shivering; DEXMEDETOMIDINE; MEPERIDINE