This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
The formula
Cerebral perfusion pressure (CPP) is the pressure gradient that drives blood through the brain:
CPP = MAP − ICP
where MAP is the mean arterial pressure and ICP the intracranial pressure. If only systolic and diastolic pressures are available, the calculator estimates MAP as diastolic + (systolic − diastolic) ÷ 3. For a CPP measurement, the arterial transducer is usually zeroed at the level of the ear (tragus), close to the base of the brain, rather than at the heart.
Why it matters
A healthy brain keeps its blood flow steady over a wide range of pressures through autoregulation. After a severe head injury, a stroke or a brain hemorrhage, swelling raises the ICP and autoregulation may fail. Blood flow then follows the CPP: too low and brain tissue becomes ischemic, too high and it can worsen swelling or bleeding.
Targets in severe traumatic brain injury
| Measure | Usual adult target (Brain Trauma Foundation, 2016) |
|---|---|
| CPP | 60 to 70 mmHg |
| ICP | treat above 22 mmHg |
| Normal ICP lying down | about 5 to 15 mmHg |
The guidelines advise against pushing CPP above 70 mmHg with fluids and vasopressors because of the risk of acute respiratory distress syndrome. Many teams now adjust the target to each patient’s autoregulation. In children, lower CPP thresholds apply, with a minimum of about 40 mmHg and age-based targets.
Example
A patient with a blood pressure of 120/70 mmHg has a MAP of about 87 mmHg. With an ICP of 15 mmHg, the CPP is about 72 mmHg. If the ICP rises to 30 mmHg at the same blood pressure, the CPP falls to 57 mmHg, below target.
Practical points
- ICP is measured with an intraventricular catheter or an intraparenchymal probe.
- Raising the head of the bed to about 30 degrees, sedation, controlled ventilation, osmotherapy and drainage of cerebrospinal fluid are common ways to lower ICP.
- Trends over time and the full clinical picture, including pupils and imaging, matter more than a single value.