Which of the following is a passive warming technique that should not be used intra-operatively to prevent hypothermia?

Warmed cotton or reflective blankets are indeed considered a passive warming technique. They primarily work by providing insulation and reducing heat loss from the body, rather than actively warming the patient. This method relies on heat retention rather than generating additional heat, which is why it may not be sufficient in an intra-operative setting where maintaining normothermia is critical.

Active warming techniques, such as forced-air warming blankets, infusion of warm IV fluids, and warm water circulating blankets, directly increase the patient's body temperature. They are designed to actively combat hypothermia by supplying warmth to the patient, making them more effective during surgeries where patients are at risk of becoming hypothermic due to anesthesia, exposure, and the cooling effects of surgical procedures.

The use of warmed cotton or reflective blankets may be more appropriate in non-operative situations or in settings where the need for aggressive temperature management is not as critical. Intra-operatively, more active measures are warranted to maintain a stable core temperature.