Cerebral perfusion pressure

Cerebral perfusion pressure, or CPP, is the net pressure gradient causing blood flow to the brain (brain perfusion). It must be maintained within narrow limits because too little pressure could cause brain tissue to become ischemic (having inadequate blood flow), and too much could raise intracranial pressure (ICP).

CPP can be defined as the pressure gradient causing cerebral blood flow (CBF) such that

<math>CBF = CPP/CVR </math>

where:

CVR is cerebrovascular resistance

The three pressures that can contribute to the CPP are:

• Mean arterial pressure (MAP)
• ICP
• Jugular venous pressure (JVP)

In many tissues, the perfusion pressure is just the pressure difference between the arterial side (the upstream pressure) and the venous side (downstream pressure). In some tissues there is a third pressure to consider and this is the pressure external to the blood vessels because if high this pressure can restrict flow through the tissue. This situation is known as a Starling resistor. Such a situation exists in the brain where the external pressure is the ICP. Consequently, the correct definition of CPP is:

<math> CPP = MAP - ICP </math> (if ICP is higher than JVP)

or

<math> CPP = MAP - JVP </math> (if JVP is higher than ICP).

Under normal circumstances (MAP between 60 to 150 mmHg and ICP about 10 mmHg) cerebral blood flow is relatively constant due to protective autoregulation. Outside of the limits of autoregulation, raising MAP raises CPP and raising ICP lowers it (this is one reason that increasing ICP in traumatic brain injury is potentially deadly). CPP is normally between 70 and 90 mmHg in an adult human, and cannot go below 70 mmHg for a sustained period without causing ischemic brain damage, although some authorities regard 50-150 mmHg as a normal range for adults. Children require pressures of at least 60 mmHg.

References

Others

• Sanders MJ and McKenna K. 2001. Mosby’s Paramedic Textbook, 2nd revised Ed. Chapter 22, "Head and Facial Trauma." Mosby.
• Walters, FJM. (1998). "Intracranial Pressure and Cerebral Blood Flow" (). Physiology (8, Article 4). Retrieved 2007-03-19. 

Steiner LA, Andrews PJ (2006). "Monitoring the injured brain: ICP and CBF". British Journal of Anaesthesia. 97 (1): 26–38. doi:10.1093/bja/ael110. PMID 16698860. 

Duschek S, Schandry R (2007). "Reduced brain perfusion and cognitive performance due to constitutional hypotension". Clinical Autonomic Research. 17 (2): 69–76. doi:10.1007/s10286-006-0379-7. PMC 1858602 Freely accessible. PMID 17106628. 

Tolias C and Sgouros S. 2003. "Initial Evaluation and Management of CNS Injury." Emedicine.com. Retrieved on March 19, 2007

Czosnyka M, Pickard JD (2004). "Monitoring and interpretation of intracranial pressure". Journal of Neurology, Neurosurgery, and Psychiatry. 75 (6): 813–821. doi:10.1136/jnnp.2003.033126. PMC 1739058 Freely accessible. PMID 15145991.