An otherwise healthy 16-year-old girl is undergoing posterior spinal fusion for thoracolumbar scoliosis. During the procedure, the most likely cause of a marked decrease in the amplitude of the somatosensory evoked potentials after stimulation of the posterior tibial nerve is
(A) administration of fentanyl 30 jag /kg for induction
(B) administration of isoflurane 1.3 MAC for maintenance
(C) administration of vecuronium 0.15 mg/kg
(D) a decrease in body temperature from 37 to 35°C
A 50-year-old patient undergoes subtotal thyroidectomy for Graves' disease. In the immediate postoperative period, he has marked hoarseness but no stridor. The most likely cause of the hoarseness is trauma to the
(A) external branch of the superior laryngeal nerve
(B) internal branch of the superior laryngeal nerve
A 72-year-old woman is somnolent one day after left carotid endarterectomy. She has smoked 2 packs of cigarettes daily for 50 years. Six weeks ago, she underwent right carotid endarterectomy. At this time, arterial blood gases while breathing room air are PO2, 45 mmHg, PCO2, 60 mmHg, and pH 7.30. Which of the following is the most likely cause of the increased PCO2?
A 20-year-old man involved in a motor vehicle accident is brought to the operating room for irrigation and debridement of open fractures of the femur and humerus. Cyanosis, decreased breath sounds on the left, increased peak airway pressure, and hypotension are noted after intubation of the trachea. The most likely cause is
A 65-kg 70-year-old man in the PACU is breathing spontaneously at 20/min through an endotracheal tube connected to a T-piece with a fresh gas flow of 5 L/min. He has a tidal volume of 350 mL and an FiO2 of 0.5. SpO2 decreases from 98% to 84% over one hour, then improves to 92% with an FiO2 of 1.0. Which of the following is the most likely cause of the hypoxemia?
(A) Decreased functional residual capacity
(B) Increased dead space ventilation
(C) Inhibition of hypoxic pulmonary vasoconstriction