An 87-kg 64-year-old woman in good general health is undergoing a right knee arthroplasty while in the supine position with general anesthesia consisting of enflurane 2% and nitrous oxide 50% in oxygen. She is breathing spontaneously through a 7-mm endotracheal tube. During the first 30 minutes of the procedure, the arterial oxygen saturation measured by pulse oximetry decreases from 98% to 92%. The most likely cause of the desaturation is
(A) decreased functional residual capacity
(B) diffusion hypoxia
(C) hypercarbia
(D) increased airway resistance produced by the endotracheal tube
(E) inhibition of hypoxic pulmonary vasoconstriction
A
Compared with healthy nonhypertensive patients, in patients with untreated hypertension undergoing anesthesia and operation,
(A) cerebral ischemia may occur at higher blood pressures
(B) intravenous fluid should be restricted before induction
(C) left ventricular hypertrophy enhances compensation for intraoperative fluid loss
(D) responses to sympathetic stimulation are decreased
(E) the incidence of intraoperative hypotension is lower
During ligation of a patent ductus arteriosus, a newborn infant receives a total gas flow of 5 L/min through a nonheated Jackson-Rees system. Operating room temperature is maintained at 30°C. The primary cause of a rapid decrease in rectal temperature from 36.8°C to 35°C is
(A) absence of the central temperature control mechanism
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 neurologically intact 48-year-old woman is scheduled for removal of a parietal lobe arteriovenous malformation. The relative risk for complete resection is to be determined by a test occlusion of the feeding artery. Which of the following intraoperative monitoring techniques is most appropriate for this test?
(A) Brain stem auditory evoked potentials
(B) Cerebral blood flow using radioactive xenon
(C) EEG
(D) Evoked potentials elicited by stimulating the posterior tibial nerve
During cardiopulmonary bypass, the perfusionist notes that the mixed venous oxygen saturation has decreased from to 55%. Which of the following is the most likely cause?
(A) Administration of a nitroprusside bolus
(B) Administration of a thiopental bolus
(C) Decrease in rectal temperature from 34°C to 28°C