In which of the following situations should caution be exercised to prevent positional asphyxia?

Caution should be exercised during the physical restraint of a subject who is struggling due to the risk of positional asphyxia in such situations. Positional asphyxia can occur when an individual's position obstructs their ability to breathe properly. When restraining a struggling person, especially in a prone position (face down), they may have difficulty breathing, which can lead to asphyxia.

In this context, maintaining the individual in a position that allows for adequate airflow is critical. Restraining techniques must be performed with care to ensure that the person’s chest and abdomen are not compressed or restricted in a way that hampers their normal respiratory function.

While other scenarios might present risks in different contexts, the immediate danger of positional asphyxia is particularly high during physical restraint due to the potential for restriction of airflow and the person's natural struggles to move, which can inadvertently place them in a harmful position.