It is now more than 5 years since the Anesthesia Patient Safety Foundation highlighted the risk of central nervous system injury following anesthesia for shoulder surgery (SS) in the Beachchair position (BCP) (click here). Although we can never be certain, it appears likely that such injuries – principally devastating stroke, results from hypoperfusion and watershed ischaemia. Most anesthetists agree that, in the seated position, the mean arterial pressure as measured by a brachial cuff, under-estimates the pressure at the circle of Willis by 15mmHg or more. The safe lower range of MAP with regard to cerebral auto regulation remains unclear, but it is certainly not below 50mmHg (click here). Regardless, if we are to believe in the “Waterfall” effect of blood pressure, then a MAP of 65mHg from an arm BP cuff is marginal. If an arterial line is place – a procedure rarely performed in orthopedic shoulder patients – the transducer should be sited at the external auditory meatus. Although there are proponents for cerebral oximetry as a monitor in this setting – I do not believe that data are sufficient to demonstrate sensitivity and specificity of this device (here). The majority of experts in the field agree that the best option is to keep BP as close to baseline as possible if general anesthesia is administered for SS in BCP (here here and here). Clearly – “induced hypotension” is a bad idea in this setting. Also, the placement of the BP cuff on the leg or ankle (so that it does not cut of the iv line periodically) would appear most unwise. In one paper from Korea (click here), ankle blood pressure was substantially higher (up to 30mmHg for systolic pressure, 20mmHg mean pressure) compared with brachial pressure in the Beachchair position. In other words – if you are using an ankle cuff, the measured blood pressure (MAP) may be 35mmHg or more higher than the pressure seen at the circle of Willis.
My own practice is to use a brachial cuff and administer a phenylephrine infusion to keep the MAP above 75mmHg (or at the normal awake range for the patient). This appears to be the best approach based on my reading of the literature and available technologies. I would urge orthopedic anesthetists in the West to read the articles referenced here and come up with their own protocols. Comments?