Final answer:
The nurse should reposition the patient and gently massage their back as per the gate control theory, which posits that activating larger nerve fibers through these actions can help block pain signals from smaller nerve fibers, providing pain relief.
Step-by-step explanation:
Based on the gate control theory, the action that a nurse should take when a patient continues to have moderate to severe incisional pain after surgery is c) Reposition the patient and gently massage the patient's back. This approach utilizes the theory's concept that non-painful input closes the "gates" to painful input, which prevents pain sensation from traveling to the central nervous system. Therefore, by repositioning the patient and providing a gentle massage, the nurse can help to activate larger nerve fibers that can block the conduction of pain signals through smaller nerve fibers, potentially providing relief from pain.
The administration of pain medications in smaller doses but more frequently is not specifically related to the gate control theory, but rather to pharmacological pain management and should be done following a doctor's prescription. Decreasing external stimuli could possibly help with the patient's comfort but doesn't directly apply to the gate control theory. Advising the patient to try to sleep would not actively engage the gate control mechanism either.