What two events render a segment of an axon temporarily insensitive or refractory to another stimulus?

Mr. will, a 67-year-old patient, is postoperative day 2 after a coronary artery bypass graft operation to revascularize his coronary arteries that were significantly blocked. he has a midline incision of his chest and a 7-inch incision on the inner aspect of his right thigh where a saphenous vein graft was harvested and used to vascularize the blocked coronary artery. the surgeon ordered oxycodone 5 mg every 4 hours prn for moderate pain and oxycodone 10 mg every 4 hours prn for severe pain. a. considering the patient's age, what medication administration considerations should the nurse incorporate into the pain management plan and why? b. what measures should the nurse provide the patient to prevent adverse effects of analgesic agents from occurring? c. what nonpharmacologic pain management methods should the nurse teach to mr. will to assist with pain management?