Step 1: Calculate the MAP
The formula given is MAP = (systolic + 2 × diastolic) ÷ 3. With a blood pressure of
112/62 mmHg, the calculation is:
MAP = (112 + 2 × 62) ÷ 3 = (112 + 124) ÷ 3 = 236 ÷ 3 =
78.7 mmHg, which rounds to
79 mmHg.
Step 2: Calculate the CPP
Cerebral perfusion pressure is the pressure gradient driving blood flow through the brain. It is defined as the difference between mean arterial pressure and intracranial pressure:
CPP = MAP − ICP =
79 − 26 = 53 mmHg.
Step 3: Compare with the unit target
The unit target is
60–70 mmHg. A CPP of
53 mmHg falls
below the lower limit of the target range, indicating that cerebral perfusion is currently inadequate.
Why this matters in severe TBI
In severe traumatic brain injury, the brain’s autoregulatory capacity is often impaired.
Cerebral perfusion pressure becomes a critical clinical variable because it reflects the net pressure available to deliver oxygen and glucose to injured but still viable brain tissue. When CPP drops too low, the risk of secondary ischemic injury rises, which can worsen neurologic outcome.
The meta-analysis by Karagianni et al. emphasizes that
CPP is the arithmetic difference between MAP and ICP and is central to maintaining cerebral blood flow after sTBI, although the exact optimal threshold remains debated
[1]. This case illustrates why continuous calculation—not just watching ICP in isolation—is essential: the ICP of
26 mmHg is above the stated ICP target of
22 mmHg or lower, and the resulting CPP of
53 mmHg confirms that both intracranial hypertension and systemic hypotension are combining to threaten brain perfusion.
The second source reinforces that
optimal cerebral perfusion pressure is an emerging individualized target, but even standard fixed targets such as
60–70 mmHg serve as a practical floor below which perfusion is generally considered unsafe in severe brain injury
[2].
Clinical priority
Watch out! A CPP below target is a reportable finding. The nurse should immediately notify the provider and anticipate interventions such as lowering ICP (e.g., ensuring sedation, head-of-bed positioning, cerebrospinal fluid drainage via the intraventricular catheter) or raising MAP (e.g., vasopressors or fluids) to restore CPP into the
60–70 mmHg range.
Key point! CPP is calculated as MAP minus ICP, not as systolic blood pressure minus ICP. Using the raw systolic value of
112 mmHg would incorrectly suggest a CPP of
86 mmHg, which is why the MAP must be computed first.
References (research sources)
- [1]
Cerebral Perfusion Pressure in Severe Traumatic Brain Injury Survivors and Non-Survivors: A Meta-Analysis.Meta-analysis/systematic reviewKaragianni M, Brotis AG, Vrettou CS, Goupou K, Stranjalis G, Fountas KN (2025) · DOI: 10.3390/brainsci15111161
- [2]
Optimal Cerebral Perfusion Pressure in Brain Injury: Physiological Relationships and Outcome.Research articlePelah AI, Kazimierska A, Czosnyka M, Hawryluk GWJ (2025) · DOI: 10.1227/neu.0000000000003411