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 MgSO 4 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°C (target range 34 to 35°C). Subjects received 1 of the following pharmacological regimens: (1) meperidine monotherapy (nϭ5); (2) meperidine plus buspirone, 30 to 60 mg PO administered at the time of initiation of cooling (nϭ4); (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 (nϭ5); or (4) meperidine, ondansetron, and MgSO 4 , 4 to 6 g IV bolus followed by 1 to 3 g per hour infusion (nϭ8). Thermal comfort was evaluated with a 100-mm-long visual analog scale. Results-More subjects who received MgSO 4 were vasodilated during hypothermia induction (7 of Key Words: hypothermia Ⅲ magnesium sulfate Ⅲ neuroprotection Ⅲ stroke T herapeutic hypothermia has been proven effective after cardiac arrest 1,2 and shows promise as a treatment for acute stroke. 3,4 Surface cooling techniques are being developed but, although noninvasive, they typically achieve slower cooling rates than endovascular methods. 5-7 MgSO 4 has antishivering effects 8,9 and may enhance the cooling rate because of its vasodilatory properties. Furthermore, MgSO 4 has potential neuroprotective effects, 10,11 and experimental data suggest the neuroprotective effect of hypothermia can be increased with combination therapy that includes MgSO 4 . 12 We assessed the hypothesis that the addition of intravenous MgSO 4 to an antishivering pharmacological regimen will increase the cooling rate when using a surface cooling technique (Arctic Sun Temperature Management System). Materials and MethodsAfter approval from the institutional review board at the University of South Alabama, healthy volunteers were recruited, and written informed consent was obtained. Exclusion criteria included any of the following: history of cryoglobulinemia, paramyotonia congenita, recent myocardial ischemia, pregnancy, or recent use of phenothiazines, monoamine oxidase inhibitors, alcohol, or narcotics. Females of childbearing potential were screened with a urine pregnancy test.All subjects underwent cardiac and neurologic examinations and 12-lead electrocardiography before initiation of cooling.Five Arctic Sun Energy Transfer Pads (Medivance, Inc) were applied to the thighs and chest and either connected to an Arctic Sun model 200 temperature control module with interfacing recirculating chiller (Kodiak RC011G02BG1; Lytron; nϭ9) or to an Arctic Sun model 2000 with integrated chiller (nϭ13). Both mode...

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: Our data suggest that Ttym and Trec are not related during the induction of hypothermia via surface cooling but correlate during the maintenance phase, with a -0.3 degrees C gradient. These findings support the use of rectal temperature as a measure of tympanic and, therefore, brain temperature during maintenance of induced hypothermia in nonintubated humans.

Mild induced hypothermia is associated with an increase in MCA FV and a decrease in MCA PI. The increase in MCA FV may be partially due to microcirculatory vasodilation.