The Insidiousness of Brain Retractor Pressure: Another “Smoking Gun”?

In Response: Albin and Bunegin call attention to an interesting, yet poorly appreciated mechanism of brain injury during elective intracranial surgery, namely excessive brain retraction pressure (BRP). They convincingly argue that the injury may be quite common and that it may affect not only the locally retracted brain region but also remote cerebral tissue. Although the notion that BRP may contribute to the early cerebral hyperemia observed by Bruder et al. (1) is worthy of serious consideration, it also evokes several questions. First, if BRP is responsible for postcraniotomy emergence hyperemia, why was the hyperemic response observed in both tumor and aneurysm surgery, when the latter presumably associates with BRP injury more frequently than the former because relatively more retraction is required in operations where little brain tissue is removed? The mechanism by which BRP would produce hyperemia is not addressed by Albin & Bunegin. Depending on the extent of ischemia, a transient luxury reperfusion phase is said to occur after ischemia brain injury (2). Yet postischemic hyperemia is frequently not observed after focal ischemia (3). Thus, BRP-related ischemia and injury might be expected to result in regions of coexisting adequate and low flow brain regions, (4) not unlikely the situation seen in closed head injury, but unlike the fairly uniform hyperemia observed by Bruder et al. If BRP is similar to traumatic cerebral contusion in its cerebral hemodynamic signature, hyperemia would not be expected, even as early as 4 hours after injury (5). The suggestion that BRP may represent another “smoking gun” in postcraniotomy hyperemia is intriguing; but to clear the smoke, the fresh winds of further mechanistic investigation need to blow even harder.