Final answer:
During surgery, evaporation is the major mode of heat loss, accounting for up to 80% of total body heat loss, while heat loss from breathing is not considered a major form.
Step-by-step explanation:
The major mode of heat loss to a patient during surgery, accounting for up to 80% of total body heat lost intraoperatively, is via evaporation. This is particularly significant because the surgical environment and the exposure of internal organs to the air can increase the rate of evaporation. In contrast, heat loss through breathing represents a much smaller portion of the body's total heat loss. When considering typical metabolic rates, the total rate of heat transfer from breathing (including both convective and evaporative components) would be 29.2 W + 9.49 W = 38.7 W. As a point of comparison, the body consumes 83 W of power while sleeping and 120 to 210 W while sitting. Therefore, breathing is not a major form of heat loss when compared to the body's overall consumption and heat loss mechanisms such as radiation, conduction, and convection, which account for other significant portions of heat exchange.