Purpose of review: There is an ever-increasing number of forced-air warming devices available in the market. However, there is also a paucity of studies that have investigated the physical background of these devices, making it difficult to find the most suitable ones.
Recent findings: Heat flow produced by power units depends on the air temperature at the nozzle and the airflow. The heat transfer from the blanket to the body surface depends on the heat exchange coefficient, the temperature gradient between the blanket and the body surface and the area that is covered. Additionally, the homogeneity of heat distribution inside the blanket is very important. The lower the temperature difference between the highest and the lowest blanket temperature, the better the performance of the blanket.
Summary: The efficacy of a forced-air warming system is mainly determined by the design of the blankets. A good forced-air warming blanket can easily be detected by measuring the temperature difference between the highest blanket temperature and the lowest blanket temperature. This temperature difference should be as low as possible. Because of the limited efficacy of forced-air warming systems to prevent hypothermia, patients must be prewarmed for 30–60 min even if a forced-air warming system is used during the operation. During the operation, the largest blanket that is possible for the operation should be used.