A 56-year-old man undergoes a left upper lobectomy. An epidural catheter is inserted for postoperative pain relief. Ninety minutes after the first dose of epidural morphine, the patient complains of itching and becomes increasingly somnolent. Blood gas measurement reveals the following: pH 7.24; PaCO2=58;PaO2=100;HCO3-=28. Initial therapy should include

**Core Concept**
Respiratory acidosis is a condition characterized by an elevated PaCO2 level, leading to a decrease in blood pH. In this scenario, the patient's PaCO2 level is 58 mmHg, indicating severe respiratory acidosis. The patient's somnolence and itching are likely symptoms of opioid-induced respiratory depression, a common side effect of epidural morphine.

**Why the Correct Answer is Right**
The patient's symptoms are consistent with opioid-induced respiratory depression, which can lead to hypoventilation and increased PaCO2 levels. The administration of epidural morphine has caused a decrease in the patient's respiratory rate, resulting in a significant increase in PaCO2. The increase in PaCO2 leads to a decrease in blood pH, causing the patient's respiratory acidosis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because administering more epidural morphine will only exacerbate the patient's respiratory depression and worsen the respiratory acidosis.

**Option B:** This option is incorrect because administering oxygen will not address the underlying cause of the patient's respiratory acidosis, which is the hypoventilation caused by opioid-induced respiratory depression.

**Option C:** This option is incorrect because administering naloxone, an opioid antagonist, is the correct treatment for opioid-induced respiratory depression. However, administering naloxone without addressing the underlying cause of the patient's respiratory acidosis (i.e., hypoventilation) will not correct the patient's pH imbalance.

**Clinical Pearl / High-Yield Fact**
Opioid-induced respiratory depression is a common side effect of epidural morphine, and it can be reversed with naloxone. However, naloxone should be administered with caution, as it can cause withdrawal symptoms in patients who have developed physical dependence on opioids.

**Correct Answer: C. Administering naloxone will reverse the opioid-induced respiratory depression and improve the patient's respiratory status.

✓ Correct Answer: D. Intravenous naloxone