Final answer:
For a client with arterial insufficiency in the lower extremities, regularly checking leg pulses is an essential nursing intervention. Option 4.
Step-by-step explanation:
An essential nursing intervention for a client with arterial insufficiency of both lower extremities is to check pulses in the legs regularly option 4. This helps in monitoring the status of blood flow in the lower limbs. While maintaining elevation of both legs may seem beneficial, it's more commonly advised for venous rather than arterial issues. Massaging painful legs or applying heat with a hot water bottle would not be recommended due to the potential risk of damaging impaired tissue and increasing pain or inflammation.