Which of the following is a limitation of active warming devices?

The limitation of active warming devices primarily lies in their dependence on power sources. Active warming devices are designed to provide controlled heat to patients, which can be particularly beneficial in preventing hypothermia or treating cold injuries. However, if a situation arises where power sources are limited—such as in remote environments, hostile settings, or after equipment malfunction—these devices may not be operational, rendering them less effective or unusable.

The other options do not correctly identify limitations of active warming devices. While it is true that they require direct contact with the skin for optimal effectiveness, this is a function of how they operate rather than a limitation in the same sense as lack of power sources. Additionally, active warming devices may not be effective in all weather conditions; they are not inherently suitable for use without taking into account various environmental factors. Lastly, while warming can facilitate improved blood flow, enhancing blood clotting is not a reason that would limit their use, as blood clotting can actually be a beneficial response in treating trauma.