During the immediate postoperative period, the Post Anesthesia Care Unit nurse is assessing a patient who had hip surgery. The patient is experiencing tachycardia, tachypnea, and muscle rigidity, and his temperature is 103°F (39.4°C). The nurse will prepare for what immediate treatment?

The correct answer is A: Dantrolene injection, a skeletal muscle relaxant. The patient is exhibiting signs of malignant hyperthermia (MH), a potentially life-threatening complication of anesthesia. Dantrolene is the definitive treatment for MH as it inhibits calcium release from the sarcoplasmic reticulum, preventing muscle rigidity and hyperthermia. CPR and intubation (B) are not indicated as the patient's airway and circulation are currently stable. An anticholinesterase drug like neostigmine (C) would exacerbate muscle rigidity in MH. Naltrexone hydrochloride (D) is used for opioid reversal, which is not relevant in this scenario.