Final answer:
The assessment finding that indicates a patient is in stage 4 NREM sleep is 'c. The patient is difficult to awaken'. This phase is characterized by low frequency and high amplitude delta waves, with significant slowing of the heart rate and respiration.
Step-by-step explanation:
When assessing a patient who is in stage 4 NREM sleep, also known as slow-wave sleep, the assessment finding that indicates this stage is c. The patient is difficult to awaken. This stage of sleep is characterized by low frequency, high amplitude delta waves, and during this time an individual's heart rate and respiration slow dramatically. Stage 4 NREM sleep is the deepest stage of sleep, making it quite challenging to wake someone who is in this phase. It is in stark contrast to REM sleep, where eyes move rapidly and the brain activity is similar to waking state. Therefore, both answer choices a. The patient awakens easily and b. The patient's eyes rapidly move are not indicative of stage 4 NREM sleep. Also, elevated vital signs, as suggested in option d, would not typically be associated with this deep sleep stage since the body is in a state of reduced physiological activity.