What this calculator does
The brain sits inside a rigid skull, so the pressure pushing blood into it is not arterial pressure alone but arterial pressure less whatever pressure is already inside. That difference is cerebral perfusion pressure.
It is why intracranial pressure matters so much. With a blood pressure of 120 over 80 the mean arterial pressure is 93.3 mmHg, and an intracranial pressure of 10 leaves 83.3 mmHg of perfusion, while 40 leaves only 53.3, below the usual adult target.
The formula
Mean arterial pressure is calculated from the systolic and diastolic readings, weighted two thirds toward diastolic. Intracranial pressure is then subtracted.
| Term | Meaning |
|---|---|
| CPP | Cerebral perfusion pressure: mean arterial pressure less intracranial pressure. |
| ICP | Intracranial pressure, normally under about 15 mmHg in an adult. |
| Target range | Typically 60 to 80 mmHg in adult neurocritical care. |
The inputs explained
| Field | What to enter |
|---|---|
| Systolic blood pressure (mmHg) | Systolic blood pressure in mmHg. |
| Diastolic blood pressure (mmHg) | Diastolic blood pressure in mmHg. |
| Intracranial pressure (mmHg) | Intracranial pressure in mmHg, measured with an intracranial monitor. |
When to use it
Managing a head injury
Perfusion pressure is a primary target in traumatic brain injury care.
Understanding why blood pressure is raised deliberately
Raising arterial pressure can maintain perfusion when intracranial pressure is high.
Reading a neurocritical care chart
Both components are monitored continuously and the derived figure is what is targeted.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does intracranial pressure erode perfusion?
The same blood pressure at four intracranial pressures.
| Intracranial pressure | Cerebral perfusion pressure | Reading |
|---|---|---|
| 5 mmHg | 88.3 mmHg | Above the typical adult target range |
| 10 mmHg | 83.3 mmHg | Above the typical adult target range |
| 25 mmHg | 68.3 mmHg | Within the typical adult target range |
| 40 mmHg | 53.3 mmHg | Below the typical adult target: a common trigger for escalating care in neurocritical patients |
Questions
Why is there a target rather than "as high as possible"?
Because both directions carry risk. Too low and the brain is underperfused; too high and there is an increased risk of respiratory complications from the interventions used to raise it. Guidelines generally suggest a range rather than a floor.
How can perfusion be improved?
Either by raising mean arterial pressure or by lowering intracranial pressure, and management usually addresses both. Which is appropriate depends on the cause and is a specialist decision.
Is the target the same for children?
No. Age-appropriate targets are lower for children and vary with age, so the adult 60 to 80 mmHg range should not be applied to paediatric patients.
What is autoregulation?
The brain's ability to keep blood flow roughly constant across a range of perfusion pressures. When it is impaired, which is common after injury, flow follows pressure directly and the perfusion figure becomes far more critical.
For mean arterial pressure on its own, see the mean arterial pressure calculator. For cardiac output feeding that pressure, see the cardiac output calculator.