Perfusion pressure is the net pressure gradient driving blood flow through an organ's vascular bed, calculated as the difference between arterial inflow pressure and venous outflow pressure (or, in the case of the brain, intracranial pressure). Cerebral perfusion pressure (CPP) = Mean Arterial Pressure (MAP) - Intracranial Pressure (ICP), with the target CPP typically 60-70 mmHg. The brain autoregulates blood flow across a MAP range of 60-150 mmHg through myogenic and metabolic mechanisms that dilate or constrict cerebral arterioles. When MAP falls below the autoregulatory range or ICP rises, CPP drops below the ischemic threshold, causing neuronal injury. Similarly, renal perfusion requires MAP > 65 mmHg to maintain glomerular filtration, and abdominal perfusion pressure (APP = MAP - intra-abdominal pressure) becomes critical in abdominal compartment syndrome.