Skin debridement operation

JD, a 15-year-old boy, is severely burned while escaping from a building fire. The extensive burns include first- and second-degree burns covering much of his body and a local, full-thickness burn on his right forearm. He reaches the emergency department in severe pain and is treated with intravenous morphine in increasing quantities until he reports that the pain has subsided. This dose of morphine is then maintained. The next day, he has surgical debridement of his burn wounds and a skin graft to his right forearm. During the operation, an anesthesiologist provides a continuous intravenous infusion of remifentanil, with a bolus dose of morphine added near the end of the operation. At the end of the operation, and for 4 days thereafter, JD receives intravenous morphine through a patient-controlled analgesia device. As the burns heal, the morphine dose is tapered and eventually replaced with an oral oxycodone/acetaminophen com- bination tablet. Three months later, JD reports severe loss of sensation to touch in the area of the skin graft. He also describes a persistent tingling sensation in this area, with occasional bursts of sharp, knife-like pain. After referral to a pain clinic, JD is prescribed oral gabapentin, which partially reduces his symptoms. However, he reports to the pain clinic again 2 months later, still in severe pain. At this time, amitriptyline is added to the gabapentin, and the pain is further relieved. Three years later, JD’s lingering pain has resolved and he no longer requires medication, but the lack of forearm sensation persists. Questions

1. What mechanisms produced and sustained the pain that lasted from JD’s exposure to the fire until his initial treatment?

2. What was the rationale for the sequence of medications used during the skin debridement operation?

3. Explain the mechanisms that could produce spontaneous pain in the region of the full-thickness burn months to years after healing of the skin and the rationale for using gabapentin to treat JD’s chronic pain.

4. Why was morphine tapered gradually and replaced with a combination oxycodone/acetaminophen tablet?