Perfusion Pressure

An acceptable blood pressure does not always mean that an organ is receiving adequate flow. Perfusion pressure is the pressure gradient across an organ: pressure entering its vascular bed minus the pressure opposing outflow. Mean arterial pressure (MAP), rather than systolic pressure alone, is the principal systemic variable used when evaluating shock and resuscitation. The downstream pressure matters. Cerebral perfusion pressure (CPP) falls when intracranial pressure (ICP) rises, even if MAP is unchanged; abdominal perfusion pressure (APP) falls when intra-abdominal pressure (IAP) rises. This is why a patient with MAP 80 mmHg and ICP 25 mmHg has a CPP of only 55 mmHg. The practical question is not simply “What is the blood pressure?” but “What pressure gradient is reaching the organ, and is it producing evidence of flow?” Targets depend on context. Severe traumatic brain injury, septic shock, and post-cardiac-arrest care use different pressure goals, and aggressively raising one pressure can create harm. In Canadian primary care, Hypertension Canada’s 2025 guideline defines hypertension at BP 130/80 mmHg or higher; pharmacotherapy is generally recommended at 140/90 mmHg or higher, or...