RAP Index [Neurosurgery Wiki]

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=====RAP Index=====
The accurate measurement of dynamic [[intracranial pressure]] is complex. Although the measurement of [[intracranial pressure]] (ICP) is an important factor in determining both the clinical management and outcome of patients with several neurosurgical conditions, recent studies have looked at the use of measuring the compensatory reserve as a possible predictor of clinical outcome and how it could be used to guide clinical management. Czosnyka et al. designed a coefficient between the mean intracranial pressure and the ICP [[mean pulse amplitude]], the RAP index, as a potential descriptor of neurological deterioration in [[traumatic brain injury]] (TBI) patients 
((Czosnyka M, Steiner L, Balestreri M, Schmidt E, Smielewski P, Hutchinson PJ, Pickard JD. Concept of “true ICP” in monitoring and prognostication in head trauma. Acta Neurochir Suppl. 2005;95:341–344. doi: 10.1007/3-211-32318-X_70.)).


RAP appears to characterize pressure-volume compensatory reserve in patients with hydrocephalus
((Kim DJ, Czosnyka Z, Keong N, Radolovich DK, Smielewski P, Sutcliffe MP, Pickard JD, Czosnyka M. Index of compensatory reserve in hydrocephalus. Neurosurgery. 2009;64(3):494–501. doi: 10.1227/01.NEU.0000338434.59141.89.)).

More studies have researched the use of the RAP index as a possible marker to guide clinical management in patients with raised ICP. This has included analysing the effects of baseline effect errors on both the RAP index as well as the ICP wave parameters, including the ICP [[mean pulse amplitude]] (AMP) 
((Eide PK, Sorteberg A, Meling TR, Sorteberg W. The effect of baseline pressure errors on an intracranial pressure-derived index: results of a prospective observational study. Bio Med Eng. 2014;13:99.))
((Steiner LA, Andrews PJD. Monitoring the injured brain: ICP and CBF. BJA 97(1) 26–38)).

These studies concluded that baseline effect errors may hinder the use of the RAP index as a marker to guide clinical management due to their influential effect on the mean ICP, which is one of two factors used to calculate the RAP index. Other studies have shown that the AMP, as opposed to the RAP index, is refractory to these baseline errors and may provide a more accurate marker to guide clinical management, as well as its potential to predict mortality in certain neurosurgical events including traumatic brain injury
((Budohoski KP, Schmidt B, Smielewski P, Kasprowicz M, Plontke R, Pickard JD, Klingelhöfer J, Czosnyka M. Non-invasively estimated ICP pulse amplitude strongly correlates with outcome after TBI. Acta Neurochir Suppl. 2012;114:121–125. doi: 10.1007/978-3-7091-0956-4_22.)).

Although further investigation needs to be undertaken in order to fully assess the role of ICP indices in guiding the clinical management of patients with raised ICP, the studies undertaken to date provide an insight into the potential role of ICP indices to treat raised ICP proactively rather than reactively and therefore help prevent or minimise secondary brain injury
((Hall A, O'Kane R. The best marker for guiding the clinical management of
patients with raised intracranial pressure-the RAP index or the mean pulse
amplitude? Acta Neurochir (Wien). 2016 Oct;158(10):1997-2009. doi:
10.1007/s00701-016-2932-z. Epub 2016 Aug 27. PubMed PMID: 27567609; PubMed
Central PMCID: PMC5025501.
)).