Compute MAP and CPP from systolic/diastolic blood pressure and intracranial pressure, with interpretation bands based on Brain Trauma Foundation targets.
MAP − ICP
MAP (mean arterial pressure) is the average driving pressure in the arteries over one cardiac cycle. CPP (cerebral perfusion pressure) is the net pressure gradient that drives oxygen-rich blood into brain tissue — the difference between MAP pushing blood in and ICP pushing back.
| Case | SBP / DBP / ICP | MAP | CPP | Status |
|---|---|---|---|---|
| Normal adult | 120 / 80 / 10 | 93.3 | 83.3 | adequate |
| Low perfusion | 90 / 60 / 18 | 70.0 | 52.0 | low |
| Wide pulse pressure | 160 / 70 / 25 | 100.0 | 75.0 | adequate |
Step-by-step for the first row: MAP = 80 + (120 − 80)/3 = 80 + 13.33 = 93.3 mmHg; CPP = 93.3 − 10 = 83.3 mmHg → adequate.
| CPP (mmHg) | Band | Meaning |
|---|---|---|
| ≥ 70 | adequate | Within or above the BTF 60–70 target range. Normal physiology is ~80 mmHg; values well above 80 usually reflect systemic hypertension. |
| 60 – 69.9 | borderline | Lower edge of the BTF target range. In clinical settings this is watched closely. |
| 50 – 59.9 | low | Below the BTF target — risk of cerebral ischemia. Medical emergency in a real patient. |
| < 50 | critical | Far below any target; brain perfusion is severely threatened. |
Key relationships: CPP < 60 mmHg should be avoided (risk of cerebral ischemia and secondary brain injury). Rising ICP lowers CPP directly (CPP = MAP − ICP): normal ICP is about 5–15 mmHg, and treatment is typically initiated above ~20–22 mmHg. In severe TBI the Brain Trauma Foundation recommends keeping CPP at 60–70 mmHg and cautions against aggressively pushing it above 70 mmHg.
Cerebral perfusion pressure is calculated as CPP = MAP − ICP, where MAP is mean arterial pressure and ICP is intracranial pressure, all in mmHg. MAP itself is estimated from blood pressure as MAP = DBP + (SBP − DBP)/3, which is the same as (SBP + 2 × DBP)/3. This definition is used by the Brain Trauma Foundation and ATLS guidelines.
Example: SBP 120 mmHg, DBP 80 mmHg, ICP 10 mmHg. First MAP = 80 + (120 − 80)/3 = 80 + 13.33 = 93.3 mmHg. Then CPP = 93.3 − 10 = 83.3 mmHg, which falls in the adequate band. A second example: SBP 90, DBP 60, ICP 18 gives MAP = 70.0 and CPP = 52.0 mmHg, which is below the 60 mmHg target (low band).
Normal physiological CPP is about 80 mmHg. In neurocritical care, the Brain Trauma Foundation recommends a target CPP of 60–70 mmHg for adults with severe traumatic brain injury, and advises avoiding CPP below 60 mmHg because of the risk of low cerebral blood flow and secondary brain injury.
CPP below 60 mmHg means the pressure driving blood into the brain may be too low, which can lead to cerebral ischemia (insufficient oxygen delivery to brain tissue). The Brain Trauma Foundation recommends avoiding CPP under 60 mmHg. Low CPP is a medical emergency that must be evaluated by clinicians with proper monitoring.
Because CPP = MAP − ICP, any rise in intracranial pressure directly lowers cerebral perfusion pressure when MAP stays the same. Normal ICP is about 5–15 mmHg; treatment is generally initiated when ICP exceeds about 20–22 mmHg. That is why controlling ICP is one of the two ways to protect CPP.
No. True intracranial pressure can only be measured with an invasive monitor (such as an external ventricular drain or parenchymal bolt) placed by a neurosurgical team. This calculator uses whatever ICP value you enter, so results are only as meaningful as the ICP number itself. Never guess an ICP value for a real patient.
MAP is the average arterial pressure over one cardiac cycle. Because diastole lasts roughly twice as long as systole at a normal resting heart rate, MAP weights diastole twice: MAP = DBP + (SBP − DBP)/3, which simplifies to (SBP + 2 × DBP)/3. For example, a blood pressure of 90/60 gives MAP = (90 + 120)/3 = 70 mmHg.
No. This is an educational definition calculator: it only computes the arithmetic of CPP = MAP − ICP. It is not a medical device and does not give medical advice. Real CPP interpretation requires invasive ICP monitoring, the clinical exam, imaging, and a physician. Always consult a qualified clinician for medical decisions.
Definitions and targets verified against: Brain Trauma Foundation, Guidelines for the Management of Severe Traumatic Brain Injury, 4th ed. (Carney et al., Neurosurgery 2017) — CPP = MAP − ICP, target 60–70 mmHg; WFSA Tutorial of the Week 264 — normal ICP 5–15 mmHg; e-safe-anaesthesia, "Cerebral blood flow and intracranial pressure" — MAP ≈ DBP + ⅓ pulse pressure, normal CPP ~80 mmHg; Springer/Neurocritical Care (2024) narrative review on BP targets after TBI. Full notes in SOURCES.md.
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