Calculating Cerebral Perfusion Pressure: Explained

What is cerebral perfusion pressure (CPP)? 

Cerebral Perfusion Pressure is the pressure required to move sufficient amounts of blood to the brain (cerebral blood flow), which maintains life and prevents brain ischemia.

• Mean arterial pressure (MAP) is the driving force that pumps blood to the brain.
• Intracranial pressure (ICP) is the force that stops blood from leaking out of the skull.

This is a health tool that determines the pressure of cerebral perfusion based on mean arterial pressure determination and either intracranial or central venous pressure

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.

What’s a normal CPP? 60 to 100 mmHg

To calculate CPP you need to know that:

CPP=MAP – ICP

*Cerebral perfusion pressure is EQUAL to the mean arterial pressure MINUS intracranial pressure

Example

To calculate it you need to know the patient’s BP and ICP:

BP: 108/72

ICP: 13

Right now we have: CPP= MAP – 13

First, we need to figure out the MAP (mean arterial pressure)…this is the pressure within a patient’s arteries during one cardiac cycle.

Formula for MAP:

SBP + 2(DBP) = MAP/3

*systolic blood pressure PLUS (diastolic blood pressure which is multiplied by 2) and then DIVIDED by 3.

72 x 2 = 144

144 + 108 = 252

252/3 = 84

MAP = 84

CPP= 84 -13

CPP= 71

It is normal….<60 mmHg: brain is not being perfused and as the MAP starts to equal the ICP the CPP will fall.

1. Here’s the patient information you have:

           BP: 130/73    ICP: 14 mm Hg

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 mm Hg

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

           CPP = 92 – 14

           CPP = 78 mm Hg

Interpretation

• Brain Trauma Foundation guidelines support a target CPP of 60-70 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 mm Hg and/or hypotension should be promptly treated. Management of elevated ICP may include decompressive craniectomy, cerebral spinal fluid drainage, hyperosmolar therapy, ventilation strategies, and sedation 

Advantages of CPP

• Easily monitored
• Can be monitored continuously
• Nursing staff familiar
• Endorsed by BTF (target CPP 50-70 mmHg)
• May prevent secondary injury from hypoperfusion (e.g. ischemia) or hyperperfusion (e.g. increased edema)
• If ICP is increasing and CPP compromised then medical management, and decompression can be carried out prior to life threatening herniation of brain contents
• Can be integrated with other monitoring (e.g. clinical and radiological)

Limitations of CPP

• Optimal CPP may be time/ patient/ pathology specifc
• Only a surrogate for cerebral blood flow (CBF)
• Cerebral vascular resistance is variable so changes in CBF may not detected by CPP
• Does not allow for differential autoregulation between normal and injured brain
• Therapy to maintain CPP can be harmful (e.g. lung injury, fluid overload, side effects of vasopressors)
• No Class I data to support use — indeed some evidence suggests that it makes no difference, and some that it may worsen outcomes
• Poor correlation between CPP and indices of brain oxygenation
• To accurately use requires insertion of ICP monitor and associated complications (e.g. bleeding, subdural haematoma, infection)
• Subject to measurement errors (e.g. ICP monitor, arterial line)
• No standardised calibration site for measurement of MAP when calculating CPP
  — for a person with 30 degrees elevation head and 30 cm distance between heart and the head, the difference in measured MAP/CPP levels will be 11 mmHg depending on if the blood pressure transducer is calibrated in the heart or head level
  — NASGBI and SBNS recommend zeroing the arterial transducer for calculation of cerebral perfusion pressure in the management of traumatic brain injury at the level of the tragus (see position statement here); which corresponds to the level of the foramen of Monro/ middle cranial fossa (as opposed to the level of the heart)

Conditions that occur due to CPP Problems

Conditions that happen because of, or that involve, perfusion pressure problems include:

• Heart attack.
• Heart failure.
• Coronary artery disease.
• Stroke.
• Cardiogenic shock.
• Cerebral hypoxia (lack of oxygen leading to brain injury).
• Atherosclerosis.
• Leg and foot ulcers.
• Reynaud’s disease.

REFERENCES

1. Kirkman MA, Smith M. Intracranial pressure monitoring, cerebral perfusion pressure estimation, and ICP/CPP-guided therapy: a standard of care or optional extra after brain injury? Br J Anaesth. 2014 Jan;112(1):35-46. PMID: 24293327.
2. Rao V, Klepstad P, Losvik OK, Solheim O. Confusion with cerebral perfusion pressure in a literature review of current guidelines and survey of clinical practise. Scand J Trauma Resusc Emerg Med. 2013 Nov 21;21(1):78. PMCID: 3843545
3. Rosner MJ, Rosner SD, Johnson AH. Cerebral perfusion pressure: management protocol and clinical results. J Neurosurg. 1995 Dec;83(6):949-62. PubMed PMID: 7490638.
4. Tameem A, Kroviddi H. Cerebral physiology. Contin Educ Anaesth Crit Care Pain 2013;13(4):113-118 
5. White H, Venkatesh B. Cerebral perfusion pressure in neurotrauma: a review. Anesth Analg. 2008 Sep;107(3):979-88. PMID: 18713917.
6. M. Smith, Cerebral perfusion pressure, BJA: British Journal of Anaesthesia, Volume 115, Issue 4, October 2015, Pages 488–490, https://doi.org/10.1093/bja/aev230
7. Mount CA, Das JM. Cerebral Perfusion Pressure. 2023 Apr 3. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan–. PMID: 30725956.

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