Intraoperative active warming is usually performed by skin warming. There are several forced-air systems on the market; forced air warming is generally described as the most effective yet feasible method of patient warming.

Augustine Biomedical (Eden Prairie, MN, USA) recently introduced a new patient warming system named "Hot Dog" with an active polymer warming upper-body blanket and a new under-body warming mattress. The polymer-heating devices consist of an electronic regulator and the polymer blankets, which are covered with a washable fabric. Conventional mains power the system. The manufacturer claims, that the new system "Hot Dog" (with combination of under body and upper body warming) is as effective as forced air warming, while not having any disadvantages of the forced air system, like: airborne infection, noise, high power consumption and hard-to-clean hose.

The investigators will compare the new Hot Dog patient warming device combination (under body + upper body) with the established warming system, which blows warm air via a mattress over the body of the patients).

Inclusion Criteria:

• The investigators will study 40 patients (18-90 years) undergoing elective orthopedic lower limb surgery at the trauma surgery unit. The patients must have normal weight (20-30 BMI), the duration of surgery should last between 2 - 3 hours.

Exclusion Criteria:

• There will be no other exclusion criteria (except severe peripheral arterial disease in the warmed extremity), as forced air patient warming is routinely used for all patients during this procedure.