Recently, a novel posterior heating system has been developed that provides enhanced pressure relief: the Laryngeal Mask Airway (LMA) PerfecTemp. Anactodal experience with this FDA-approved system suggests that the PerfecTemp warmer is effective, even in open abdominal surgery. The investigators therefore propose to test the hypothesis that intraoperative distal esophageal (core) temperatures with PerfecTemp warming are non-inferior to upper-body forced-air warming in patients undergoing open major abdominal surgery under general anesthesia.

Secondary hypotheses include that:

1. intraoperative core temperatures are superior with PerfecTemp than upper-body forced-air warming
2. final intraoperative core temperature is non-inferior with PerfecTemp than upper-body forced-air warming
3. final intraoperative core temperature is superior with PerfecTemp than upper-body forced-air warming.

Inclusion Criteria:

• Body-mass index 20-36 kg/m2
• Age 18-75 yrs
• ASA Physical Status 1-3
• Supine position (with or without lithotomy)

Exclusion Criteria:

• Pre-operative fever
• Serious skin lesions
• And contraindication to either PerfecTemp or forced-air warming

Most baseline characteristics were well balanced be- tween the randomized groups. However, patients assigned to resistive heating were more likely to have higher ASA physical status classification. Thus, ASA status was adjusted for in all analyses. Patients in each warming group were given comparable doses of volatile anesthesia and opioid.

In-hospital