A healthy, spontaneously breathing, supine, anesthetized patient has an arterial to end-tidal carbon dioxide tension difference of 3 mmHg. Following institution of mechanical ventilation the value increases to 12 mmHg. The most likely cause of this change is
(A) cephalad displacement of the diaphragm
(B) decreased production of carbon dioxide
(C) increased cardiac output
(D) increased shunting of blood through dependent lung zones
(E) increased ventilation of nondependent lung zones
Two months ago a 68-year-old man with insulin-dependent diabetes mellitus had a transurethral resection of the prostate under spinal anesthesia with tetracaine plus epinephrine. He now has numbness and tingling in both feet and disturbance of gait. Physical examination demonstrates stocking-type hypesthesia of both feet and ankles. The most likely diagnosis is
(A) anterior spinal artery syndrome
(B) diabetic neuropathy
(C) adhesive arachnoiditis
(D) cauda equina syndrome
(E) peripheral nerve injury from the lithotomy position
During anesthesia with nitrous oxide, oxygen, and a relaxant, the patient's lungs are being mechanically ventilated and there is a heated humidifier in the circuit. The most likely cause of an apparent increase in inspired oxygen concentration is
(A) a hole in the ventilator bellows
(B) backflow of fresh gas because of resistance in the humidifier