Cerebral perfusion pressure (CPP) is the amount of pressure needed to maintain blood flow to the brain. CPP is regulated by two balanced opposing forces:

• Mean arterial pressure (MAP) is the driving force that pushes blood into the brain.
• Intracranial pressure (ICP) is the force that keeps blood out.

Indications

CPP monitoring is useful in guiding management of patients with traumatic brain injury, poor grade subarachnoid hemorrhage, stroke, intracerebral hematoma, meningitis, acute liver failure, and hydrocephalus.

Formula

CPP = MAP – ICP
Example

1. Here’s the patient information you have:

           BP: 130/73    ICP: 14 mmHg

2. Use the formula: CPP = MAP – 14
3. Calculate the MAP, using the formula MAP = [SBP + 2(DBP)] ÷ 3

           MAP = [130+2(73)] ÷ 3

           MAP = (130+146) ÷ 3

           MAP = 276 ÷ 3

           MAP = 92 mmHg

4. Substitute the ICP and MAP into the CPP formula.

           CPP = 92 – 14
           CPP = 78 mmHg

Interpretation

• Brain Trauma Foundation guidelines support a target CPP of 50-70 mmHg in patients with severe traumatic brain injury (Carney et al, 2019).
• Maintaining the CPP within target range may prevent secondary injury from hypoperfusion (e.g. ischemia) or hyperperfusion (e.g. increased edema).
• Brain monitoring techniques such as transcranial doppler (TCD)/duplex sonography, differences between arterial and arterio-jugular venous oxygen (AVDO2), and measurements of local tissue oxygen provide complementary and specific information that may help identify the optimal CPP and ICP targets for individual patients.

Management principles 

• To achieve adequate CPP, clinicians must balance treating the underlying cause of elevated ICP and appropriately supporting the patient’s blood pressure.
• Even if the CPP is within acceptable range, elevations in ICP above 20-25 mmHg and/or hypotension should be promptly treated (Smith and Amin-Hanjani, 2019).

References:
Kirkman, M.A. and Smith, M. (2014, January). Intracranial pressure monitoring, cerebral perfusion pressure estimation, and ICP/CPP-guided therapy: a standard of care or optional extra after brain injury?  British Journal of Anaesthesia, 112(1): 35–46.

Smith, E.R., and Amin-Hanjani, S. (2019). Evaluation and management of elevated intracranial pressure in adults. UpToDate. Retrieved from: https://www.uptodate.com/contents/evaluation-and-management-of-elevated-intracranial-pressure-in-adults

Carney, N., Totten, A.M., O’Reilly, C et al. (2016, September). Guidelines for the Management of Severe Traumatic Brain Injury, 4^th Edition. Brian Trauma Foundation. Retrieved from: https://www.braintrauma.org/uploads/03/12/Guidelines_for_Management_of_Severe_TBI_4th_Edition.pdf