Magnesium sulfate increases the rate of hypothermia via surface cooling and improves comfort.

BACKGROUND AND PURPOSE Therapeutic hypothermia shows promise as a treatment for acute stroke. Surface cooling techniques are being developed but, although noninvasive, they typically achieve slower cooling rates than endovascular methods. We assessed the hypothesis that the addition of intravenous MgSO4 to an antishivering pharmacological regimen increases the cooling rate when using a surface cooling technique. METHODS Twenty-two healthy volunteers were studied. Hypothermia was induced using a surface technique with a target tympanic temperature (Ttym) of 34.5 degrees C (target range 34 to 35 degrees C). Subjects received 1 of the following pharmacological regimens: (1) meperidine monotherapy (n=5); (2) meperidine plus buspirone, 30 to 60 mg PO administered at the time of initiation of cooling (n=4); (3) meperidine and ondansetron, 8 to 16 mg IV administered as an 8 mg bolus at the time of initiation of cooling with an optional second dose after 4 hours as needed for nausea (n=5); or (4) meperidine, ondansetron, and MgSO4, 4 to 6 g IV bolus followed by 1 to 3 g per hour infusion (n=8). Thermal comfort was evaluated with a 100-mm-long visual analog scale. RESULTS More subjects who received MgSO4 were vasodilated during hypothermia induction (7 of 8 [88%] versus 4 of 14 [29%]; P=0.024). MgSO4 (coefficient -17.265; P=0.039), weight (1.838, 0.001), and the initial 2-hour meperidine dose (0.726, 0.003) were found to significantly impact the time to achieve Ttym of 35 degrees C. Subjects who received MgSO(4) had significantly higher mean comfort scores than those who did not (48+/-15 versus 38+/-12; P<0.001). CONCLUSIONS Administration of intravenous MgSO(4) increases the cooling rate and comfort when using a surface cooling technique.