A 68-year-old man undergoes elective total hip replacement under general anesthesia. Postoperatively, he is prescribed intravenous patient-controlled analgesia (PCA) with morphine. Which of the following is the most common complication encountered with PCA use in the immediate postoperative period?

Explanation

## Most Common Complication of PCA **Key Point:** Nausea and vomiting (PONV) is the most frequent adverse effect reported with opioid-based PCA systems, occurring in 20–40% of patients in the immediate postoperative period. ### Pathophysiology Opioids trigger nausea through multiple mechanisms: 1. Direct stimulation of the chemoreceptor trigger zone (CTZ) 2. Increased vestibular sensitivity 3. Delayed gastric emptying 4. Increased intracranial pressure ### Comparison of PCA Complications | Complication | Incidence | Severity | Onset | |---|---|---|---| | Nausea/Vomiting | 20–40% | Mild–moderate | 0–6 hours | | Respiratory depression | 1–2% | Severe | Variable | | Urinary retention | 5–15% | Mild–moderate | 2–24 hours | | Pruritus | 5–10% | Mild | 2–6 hours | **Clinical Pearl:** Postoperative nausea and vomiting (PONV) is the most common reason for patient dissatisfaction with PCA, even though respiratory depression is more serious. Prophylactic antiemetics (ondansetron, dexamethasone) are routinely co-prescribed with opioid PCA. **High-Yield:** The incidence of PONV with morphine-based PCA is significantly higher than with non-opioid analgesics or multimodal analgesia (which combines opioids with NSAIDs, regional blocks, or acetaminophen). ### Risk Factors for PONV with PCA - Female sex - History of motion sickness or PONV - Type of surgery (abdominal, gynecologic > orthopedic) - Volatile anesthetic use - Inadequate antiemetic prophylaxis **Warning:** Respiratory depression, though less common (1–2%), is the most serious complication and requires vigilant monitoring. However, the question asks for the *most common*, not the most serious. [cite:Miller's Anesthesia 8e Ch 40]