PATIENT-CONTROLLED ANALGESIA
Brief History. S.G., a 61-year-old man, was being treated for severe osteoarthritis in the right knee. Following an unsuccessful course of conservative therapy, S.G. was admitted to the hospital for a total knee replacement. The surgery was performed successfully, and PCA was instituted for postoperative pain management. PCA consisted of an external syringe pump connected to an IV catheter. The analgesic, meperidine (Demerol), was used at a concentration of 10 mg/mL. Parameters for PCA were set by the physician to allow a demand dose of 1 mL (10 mg) with a lockout interval of 10 minutes. An initial or loading dose of 10 mg was also provided at the conclusion of the surgery. Physical therapy was initiated at the patient’s bedside on the afternoon following surgery. The therapist found the patient asleep and impossible to arouse. Family members who were present in the room said that he had been asleep since returning to his room.
Problem/Influence of Drug Therapy. The therapist was concerned because the patient was unresponsive to any commands. His breathing seemed labored and the color of his skin and mucous membranes had a slight, distinct bluish twinge indicative of cyanosis. The therapist noticed the pulse oximeter on his fi nger, which indicated hemoglobin saturation was 86 percent, well below normal values (i.e., 95 to 100 percent). The pulse oximeter normally has an alarm set for 90 percent, but this alarm had been shut off. The therapist immediately notifi ed the nurses, who intervened and discontinued the PCA drug delivery. This device had been administering excessive amounts of opioid, resulting in unresponsiveness and decreased respiration.
1. How can PCA cause respiratory problems?
2. What are some possible reasons for the apparent overdose observed in this case?
