Safety issue

Hypothermia during surgery and in the postoperative period is associated with adverse outcomes including impaired drug metabolism, cardiac morbidity, shivering, impaired immune function, coagulopathy, and increased use of hospital resources. Several clinical studies have demonstrated that maintenance of normothermia during the perioperative period significantly reduces morbidity.

Mercury Biomed has developed a patient-warming system, WarmSmart, that potentially transfers adequate heat through hands and feet based on the physiological principle of peripheral arterio-venous shunt vaso-dilation. The technology works as a two-step process by selective thermal stimulation along the spinal cord to up-regulate blood flow to arterio-venous shunts and triggering arterio-venous shunt vasodilation and by applying circulating water heat exchangers to the palmar and plantar glabrous skin to warm highly perfused shunts in that area.

General anesthesia reduces the vasoconstriction threshold (triggering core temperature) by 1-2°C, thus promoting arteriovenous shunt dilation. It remains unknown, though, whether cervical spine warming further augments arterio-venous shunt dilation during general anesthesia. If spine heating proves unnecessary under anesthesia, Mercury Biomed's WarmSmart warming could be simpler and less expensive. Investigators therefore propose to test the hypothesis that cutaneous heating near the cervical spine does not further augment arterio-venous flow in fingers during general anesthesia.

Investigators propose to enroll ten patients. The patients will be pre-warmed and warmed intraoperatively with forced-air to maintain a core temperature near 36°C.

A ThermaZone® Device capable of heating the cervical spine area will be positioned behind the patient's neck upon arrival in the operating rooms. Additionally a forced-air warmer will be positioned appropriately and activated as soon as practical, usually after prepping and draping. Ambient temperature will be maintained near 20°C.

After about one hour of anesthesia when temperature and other factors are stable, investigators will start a 30-minute observation period. Thereafter investigators will activate the cervical spine warming system for 30 minutes (warming measurement period) and thereafter have a 30 minutes control period again.

Measurements will be recorded such as mean-skin temperature, distal esophageal temperature, MAC fraction, mean-arterial pressure and finger blood flow.

Inclusion Criteria:

1. Body-mass index 20-33 kg/m2;
2. Age 18-70 yrs;
3. ASA Physical Status 1-3.

Exclusion Criteria:

1. Serious skin lesions on the hands or arms;
2. History of serious vascular disease in the arms, including Raynaud's Syndrome;
3. Pre-operative fever or infection;
4. Surgery expected to be supine and in neutral position.