ROBERT M. POWELL AND DONAL J. BUGGY
University Department of Anaesthesia, Leicester University, Leicester, United Kingdom
Anesth. Analg., 90: 1423–1427, 2000
The neurotransmitter pathways involved in the mechanism of postanesthetic shivering (PAS) are poorly understood, but probably involve multiple levels of information integration and numerous neurotransmitters. Meperidine, clonidine, and physostigmine are effective treatments, indicating that opioid, α2-adrenergic, and anticholinergic systems are likely involved. Various observations suggest that the serotonergic system has a role in the control of PAS. Ondansetron, a 5-HT3 antagonist, may affect perioperative thermoregulation and PAS. This randomized, placebo-controlled, double-blinded study evaluated the effect of ondansetron, given just before anesthesia induction, on the typical core-to-peripheral temperature redistribution evoked by general anesthesia and on the incidence of PAS.
The 82 patients, aged 18 to 60 yr, were scheduled for orthopedic, general, or urologic surgery. Group O4 (n = 27) received 4 mg ondansetron IV, group O8 (n = 27) received 8 mg ondansetron IV, and group C (n = 28) received saline IV as a negative control immediately before the induction of anesthesia. Core and fingertip temperatures were recorded. Anesthesia was induced with IV fentanyl and propofol and maintained with I minimum alveolar anesthetic concentration isoflurane in 70% nitrous oxide/oxygen. Patients were not actively heated. PAS was documented clinically during recovery by nursing staff, who were unaware of the group assignment. Shivering was defined as readily detectable fasciculations or tremors of the face, trunk, or limbs for a minimum of 15-sec duration.
Demographic data, sex, and duration of anesthesia were similar among the groups. The incidence of PAS was 15% in patients in the O8 group compared with 57% in the saline control group, a significant difference. Patients in the O4 group had an intermediate incidence of 33%, not significantly different from either of the other groups. Mean arterial pressure and heart rate decreased compared with baseline after the induction of anesthesia, with pressure values remaining lower than baseline for the duration of the administration of anesthesia, but heart rates tending to recover to preinduction values after surgery began. There were no significant differences among the groups at any time.
Within each group core temperature decreased and fingertip temperature increased significantly, but there were no significant differences among the groups at any time interval. Visual analog scale pain scores were low in all groups at 15 min after arousal, with the control, O4, and O8 groups having mean scores of 2.1, 2.3, and 1.9, respectively.
Ondansetron, 8 mg, given before the induction of anesthesia, reduces the incidence of PAS in adults, without affecting the core-to-peripheral redistribution of temperature normally observed during the administration of general anesthesia. This finding suggests that serotonergic pathways are involved in the multifactorial regulation of PAS.
This prospective, randomized, double-blind study of 87 patients undergoing elective minor surgery demonstrates that ondansetron can be quite effective in reducing the incidence of postanesthetic shivering (PAS). In addition, it seems that this effect is dose-dependent, and may require rethinking of the standard dose of ondansetron used to treat postoperative nausea and vomiting if one is to also take advantage of the PAS-sparing effects of this drug.
PAS is not only unpleasant but may be life-threatening in the patient with significant coronary artery disease emerging from general anesthesia. It appears that ondansetron decreases PAS without directly affecting temperature in the patient. The authors of this study found no difference in the core to peripheral temperature changes that occur on induction of general anesthesia. Therefore, ondansetron is acting centrally to decrease the brain’s response to the decrease in core temperature associated with general anesthesia. Other cheaper drugs have been used to decrease PAS (i.e., meperidine or neostigmine) but none have the excellent drug profile of ondansetron. The lack of hemodynamic, sedative, and central nervous system effects makes it extremely safe to administer in the PACU to patients emerging from general anesthesia. Another avenue of future study with this drug and other 5-HT3 antagonists is in the area of shivering related to epidural and spinal anesthesia.
Roxanne Zarmsky M.D.