Intracranial pressure

The cranial cavity is a closed compartment and any breach to this confined space secondary to neurosurgery or trauma cause an imbalance between atmospheric pressure and intracranial pressure.

Intracranial pressure (ICP) is derived from the circulatory cerebrospinal fluid dynamics and cerebral blood flow that occur within the rigid intracranial compartment 1).

Intracranial pressure (ICP) is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid (CSF). The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF.

CSF pressure has been shown to be influenced by abrupt changes in intrathoracic pressure during coughing (intraabdominal pressure), valsalva (Queckenstedt's maneuver), and communication with the vasculature (venous and arterial systems). ICP is measured in millimeters of mercury (mmHg) and, at rest, is normally 7–15 mmHg for a supine adult.

Changes in ICP are attributed to volume changes in one or more of the constituents contained in the skull.

Influenced by jugular venous pressure

In normal circumstances the ICP is kept in its normal range, maintaining the relationship between the cerebrospinal fluid (CSF), the intracerebral blood, and brain tissue constant.

see Monro-Kellie hypothesis.

Adults <10–15 mm Hg

Children 3–7 mm Hg

Term infants 1.5–6 mm Hg.

Cerebrospinal fluid pressure, as measured by lumbar puncture (LP), is 10-18 cmH2O (8-15 mmHg or 1.1-2 kPa) with the patient lying on the side and 20-30 cmH2O (16-24 mmHg or 2.1-3.2 kPa) with the patient sitting up.

In newborns, CSF pressure ranges from 8 to 10 cmH2O (4.4–7.3 mmHg or 0.78–0.98 kPa). Most variations are due to coughing or internal compression of jugular veins in the neck. When lying down, the cerebrospinal fluid as estimated by lumbar puncture is similar to the intracranial pressure.

see intracranial hypertension.

see intracranial hypotension

Measurement of intracranial pressure (ICP) and mean arterial pressure (MAP) is used to derive cerebral perfusion pressure (CPP) and to guide targeted therapy of acute brain injury (ABI) during neurointensive care.

A “normal” ICP should not be considered only in light of a particular cut-off value, because waveform analysis of the ICP is also important. ICP waveform analysis can provide information on the state of cerebrovascular reactivity (PRx) and can be used to estimate optimal cerebral perfusion pressure levels for individual patients 2)

ICP, as monitored and managed according to Brain Trauma Foundation (BTF) guidelines, is not associated with ICU length of stay 3).

Czosnyka M, Pickard JD. Monitoring and interpretation of intracranial pressure. J Neurol Neurosurg Psychiatry. 2004;75:813–821. doi: 10.1136/jnnp.2003.033126.
Barone DG, Czosnyka M. Brain Monitoring: Do We Need a Hole? An Update on Invasive and Noninvasive Brain Monitoring Modalities. ScientificWorldJournal. 2014 Jan 23;2014:795762. eCollection 2014. Review. PubMed PMID: 24672373; PubMed Central PMCID: PMC3930194.
Lazaridis C, Yang M, DeSantis SM, Luo ST, Robertson CS. Predictors of intensive care unit length of stay and intracranial pressure in severe traumatic brain injury. J Crit Care. 2015 Aug 5. pii: S0883-9441(15)00435-9. doi: 10.1016/j.jcrc.2015.08.003. [Epub ahead of print] PubMed PMID: 26324412.
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