Intracranial Pressure: More Than a Number

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✓Many doctors involved in the critical care of head-injured patients understand intracranial pressure (ICP) as a number, characterizing the state of the brain pressure–volume relationships. However, the dynamics of ICP, its waveform, and secondarily derived indices portray useful information about brain homeostasis. There is circumstantial evidence that this information can be used to modify and optimize patients' treatment. Secondary variables, such as pulse amplitude and the magnitude of slow waves, index of compensatory reserve, and pressure–reactivity index (PRx), look promising in clinical practice. The optimal cerebral perfusion pressure (CPP) derived using the PRx is a new concept that may help to avoid excessive use of vasopressors in CPP-oriented therapy. However, the use of secondary ICP indices remains to be confirmed in clinical trials.

Abbreviations used in this paper:ABP = arterial blood pressure; CBF= cerebral blood flow; CMRO2 = cerebral metabolism O2 rate; CPP = cerebral perfusion pressure; ICP = intracranial pressure; PET = positron emission tomography; PRx = pressure-reactivity index; RAP = correlation between pulse amplitude and mean intracranial pressure; TBI = traumatic brain injury; TCD = trancranial Doppler.

✓Many doctors involved in the critical care of head-injured patients understand intracranial pressure (ICP) as a number, characterizing the state of the brain pressure–volume relationships. However, the dynamics of ICP, its waveform, and secondarily derived indices portray useful information about brain homeostasis. There is circumstantial evidence that this information can be used to modify and optimize patients' treatment. Secondary variables, such as pulse amplitude and the magnitude of slow waves, index of compensatory reserve, and pressure–reactivity index (PRx), look promising in clinical practice. The optimal cerebral perfusion pressure (CPP) derived using the PRx is a new concept that may help to avoid excessive use of vasopressors in CPP-oriented therapy. However, the use of secondary ICP indices remains to be confirmed in clinical trials.

Abbreviations used in this paper:ABP = arterial blood pressure; CBF= cerebral blood flow; CMRO2 = cerebral metabolism O2 rate; CPP = cerebral perfusion pressure; ICP = intracranial pressure; PET = positron emission tomography; PRx = pressure-reactivity index; RAP = correlation between pulse amplitude and mean intracranial pressure; TBI = traumatic brain injury; TCD = trancranial Doppler.

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Contributor Notes

Address reprint requests to: Marek Czosnyka, Ph.D., Academic Neurosurgery, Box 167, Addenbrooke's Hospital, Cambridge CB2 2QQ, United Kingdom. email: MC141@medschl.cam.ac.uk.Dr. M. Czosnyka is on leave from Warsaw University of Technology, Poland.
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