Background and Goal of Study: postoperative shivering is a common problem during anesthesia. The incidence of shivering is up to 40-60%, even in regional anesthesia. Shivering produces an important increment in the metabolic activity and an oxygen consumption up to 100%. Also, it has been related with a higher risk of myocardial ischemia, arterial hypoxia, increases in the intracranial and intraocular pressures; cardiac output, peripheral resistance, carbon dioxide production and lactic acidosis. Perioperative hypothermia and shivering are usually prevented using physical methods, like surface warming; and pharmacologically, with drugs like ketamine and magnesium sulphate obtaining good results.
Objective: To compare the efficacy of low doses of ketamine and magnesium sulphate as preventive agents of shivering in patients undergoing general anesthesia.
Materials and Methods: It was a prospective, double-blind and random study, including 90 patients ASA I-II undergoing general anesthesia; divided in three groups of 30 patients each one. Group K received ketamine 0,4 mg/ kg; group M received magnesium sulphate 50 mg/kg and group C received 20 mL of physiological solution. Each solution was administered ten minutes before the end of surgery. Shivering was graded using grada scale described by Crossley y Mahajan at 10, 20 and 30 minutes after surgery.
Results and Discussion: There were significantly more patients who experienced less shivering, at different times of measure (10, 20 and 30 minutes), in the group K (76,6%; 76,6%; 63,3%) than the group M (43%; 53,3%; 76,6%) respectively. In base to these results, ketamine was more effective than magnesium sulphate during the first 20 minutes after surgery with few adverse events, meanwhile, the magnesium sulphate group presents a better effect preventing shivering only at 30 minutes after the drug was administered. However, the ideal drugs for prevention of shivering, are those having a longer lasting effect. This is the only study comparing these drugs for prevention of postoperative shivering.
Conclusion(s): Low doses of ketamine are more effective than magnesium sulphate for prevention of postoperative shivering.