A patient is undergoing a craniotomy in the sitting position. Mean arterial pressure measures 80 mmHg from a radial artery catheter located 27 cm below the right atrium and a transducer located, zeroed, and calibrated at the level of the right atrium. The circle of Willis is 27 cm above the right atrium. Intracranial pressure is 0 cmH20 and right atrial pressure is 5 cmH20. The cerebral perfusion pressure in mmHg is
(A) 75
(B) 60
(C) 53
(D) 48
(E) 26
B
A 62-year-old patient undergoes resection of a descending thoracic aneurysm under anesthesia with morphine, nitrous oxide, oxygen, and pancuronium. In spite of normal somatosensory evoked potentials (SSEP) during the procedure, the patient has paraplegia postoperatively. The factor most likely responsible for failure to note the deficit intraoperatively is
(A) the effect of nitrous oxide on SSEP
(B) the effect of morphine on SSEP
(C) failure to test motor pathways
(D) hyperventilation to a PaC02 of 30 mmHg
(E) unintentional hypothermia to 34°C
C
A 65-kg man is scheduled for wrist surgery with intravenous regional anesthesia with 0.5% lidocaine 50 ml. Which of the following statements is true?
(A) This anesthetic is contraindicated if the patient has sickle cell disease
(B) Mottling of the skin after injection dictates abandonment of the technique
(C) Tourniquet discomfort is an indication to inject more local anesthetic
(D) Bupivacaine 0.5% could be substituted to prolong anesthesia
(E) Epinephrine (1:400,000) should be added to prolong anesthesia
A 25-year-old woman is admitted to the hospital in the early stages of labor at term. Initial hematocrit is 33%. Which of the following is the most likely cause of the hematocrit value?