What it is
Cerebral perfusion pressure (CPP) is the net pressure gradient that drives blood flow — and therefore oxygen — to the brain. It is the difference between the pressure pushing blood in (mean arterial pressure) and the pressure resisting it inside the skull (intracranial pressure). In severe traumatic brain injury and other causes of raised ICP, maintaining an adequate CPP is a core therapeutic target: too low and the brain ischaemias, too high and you risk hyperaemia and oedema.
The formula
CPP = MAP − ICP
Both values in mmHg. MAP comes from an invasive arterial line (or MAP = DBP + ⅓(SBP − DBP)); ICP from an intraparenchymal or intraventricular monitor.
Age-banded targets
The minimum acceptable CPP rises with age. Per the pediatric severe-TBI guidelines:
| Age band | Minimum target CPP |
|---|---|
| Infant / young child | ≥ 40 mmHg |
| Child | ≥ 50 mmHg |
| Adolescent | ≥ 55 mmHg |
There is an absolute floor of ≥ 40 mmHg at any age — a CPP below 40 is critically low regardless of band. Broadly, target the 40–50 mmHg range in younger children and 50–60 mmHg in adolescents.
When to use it
- Titrating MAP (vasopressors/fluids) and ICP (osmotherapy, CSF drainage, sedation) in severe TBI.
- Any condition with invasive ICP monitoring and raised intracranial pressure.
Worked example
A 4-year-old child (child band, target ≥50) has MAP 70 mmHg and ICP 18 mmHg.
CPP = 70 − 18 = 52 mmHg — just above the age target. If ICP then climbs to 25 mmHg, CPP falls to 45 mmHg: now below the ≥50 target (though above the 40 floor), prompting escalation of ICP control or MAP support.
Pitfalls
- Zero both transducers at the same reference (tragus / foramen of Monro). A mismatched arterial and ICP reference produces a falsely reassuring or alarming CPP.
- CPP requires invasive monitoring. It is not a non-invasive bedside estimate.
- Mind the floor and the band. A number above 40 isn’t automatically adequate — check it against the age target.
- CPP is a surrogate for cerebral blood flow, not flow itself. Autoregulation may be impaired; pair CPP with multimodal monitoring where available, and avoid aggressive CPP-driving with fluids/pressors that risk ARDS.
Run it: Cerebral Perfusion Pressure (CPP): MAP − ICP and the Age-Banded Targets
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.