← Anatomy & Physiology

Cerebral perfusion pressure

Perfusion of the brain depends on the pressure gradient across it, not on systemic blood pressure alone:

CPP = MAP − ICP

A patient with a MAP of 80 and an ICP of 25 has a CPP of 55, despite a blood pressure that looks entirely reasonable. Raising the MAP and lowering the ICP are the only two levers available, and in most situations both are worth pulling.

Measurement technique matters more than it is usually given credit for. The arterial transducer should be levelled at the tragus (approximating the foramen of Monro) rather than the phlebostatic axis; levelling at the heart instead overstates CPP by roughly 10 mmHg in a head-up patient.