A patient is undergoing shoulder surgery in the beach chair position. The mean arterial pressure measured via noninvasive cuff is 80 mm Hg, and the vertical distance from the cuff to the external auditory meatus is 36 cm. Which of the following is the best approximation of the mean arterial pressure (MAP) at the circle of Willis?

The beach chair position is used in approximately of two-thirds of the shoulder surgeries in the United States. This position offers several surgical advantages, but it is not without risk. One of the most serious risks from surgery in the beach chair position is cerebral ischemia. There are multiple reports of both transient and permanent neurological impairment due to decreases in cerebral oxygenation and perfusion while undergoing surgery in the beach chair position.

In the unanesthetized state, sitting upright results in a...

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