Articles  |   January 2013
ACE Question
Article Information
Education / CPD / Articles
Articles   |   January 2013
ACE Question
ASA Monitor 01 2013, Vol.77, 24.
ASA Monitor 01 2013, Vol.77, 24.
A patient with a history of cerebrovascular disease is scheduled for shoulder surgery. The surgeon requests that the patient be placed in the “beach chair” position. Which statement about blood pressure (BP) monitoring in this patient is MOST likely true?
There are multiple case reports and even a case series describing cerebral ischemic events in patients undergoing surgery and anesthesia performed in the “beach chair” position. Unrecognized/untreated cerebral hypotension is described as the most likely etiology of these events.
In any upright position, including the beach chair position, the blood pressure (BP) measured in the arm will be higher than the BP in the brain. The difference between the two is the hydrostatic pressure gradient between the brain and the location in which the BP is being measured. There is approximately a 0.77 mm Hg decrease for each centimeter difference in height. In most adults placed in a beach chair position, there will be approximately a 10–30 cm difference in height between a BP cuff located on the upper arm and the external auditory meatus, which represents the base of the brain. This means that the BP in the brain will be 8–24 mm Hg lower than the BP measured by a cuff located on the upper arm. In the sitting position, the circle of Willis is located an additional 10–12 cm above the base of the brain, resulting in a BP that is about 9 mm Hg lower at the circle of Willis than at the external auditory meatus. Especially in patients with cerebrovascular disease or those in whom controlled hypotension is requested by the surgeon, failure to recognize that the BP in the brain is 17–33 mm Hg lower than the BP reported by the BP cuff may easily result in cerebral perfusion pressures below the lower limit of autoregulation. Because the vertical distance between a BP cuff placed on the lower extremity and any cerebral structure is even greater, the magnitude of this difference becomes even more critical. For example, if a BP cuff on the leg is 36 cm below the external auditory meatus, the cuff will record a pressure 28 mm Hg higher than will be present at the base of the brain.
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