Abstract
Since Monro published his observations on the nature of the contents of the intracranial space in 1783, there has been investigation of the unique relationship between the contents of the skull and the intracranial pressure (ICP). This is particularly true following traumatic brain injury (TBI), where it is clear that elevated ICP due to the underlying pathological processes is associated with a poorer clinical outcome. Consequently, there is considerable interest in monitoring and manipulating ICP in patients with TBI. The two techniques most commonly used in clinical practice to monitor ICP are via an intraventricular or intraparenchymal catheter with a microtransducer system. Both of these techniques are invasive and are thus associated with complications such as hemorrhage and infection. For this reason, significant research effort has been directed toward development of a non-invasive method to measure ICP. The principle aims of ICP monitoring in TBI are to allow early detection of secondary hemorrhage and to guide therapies that limit intracranial hypertension (ICH) and optimize cerebral perfusion. However, information from the ICP value and the ICP waveform can also be used to assess the intracranial volume–pressure relationship, estimate cerebrovascular pressure reactivity, and attempt to forecast future episodes of ICH.
Highlights
The pathophysiology of traumatic brain injury (TBI) can be divided into primary and secondary injury
Normal intracranial pressure (ICP) in healthy adults is usually regarded as 5–15 mmHg [3] and in TBI an ICP of >20 mmHg is widely accepted as intracranial hypertension (ICH) [4]
Shapiro found that a pressure– volume index (PVI) reduced by 80% of control values was predictive of raised ICP in pediatric TBI [22]
Summary
The field of ICP research is a wide ranging one and, to date, has been the subject of 15 international symposia embracing such diverse disciplines as neurosurgery, intensive care, anesthesia, radiology, biophysics, electronic and mechanical engineering, mathematics, and computer science [92]. Using 24 metrics of the ICP waveform, it was possible to classify recording segments as either control or pre-IH prior to episodes of elevation of ICP to >20 mmHg over a period of at least 20 min This was done with a sensitivity of 37 and 21% and specificity of 99 and 99% for 5 and 20 min, respectively. Using 4 h windows of minute-by-minute recordings of ICP and MAP, Guiza et al generated over 1000 potential dynamic predictors from which a subset of 73 was selected These included median values for non-overlapping time intervals, measures of variability, clustering of values based on their trajectory, frequency domain analysis, and correlation of ICP with MAP. The applicability of the technique to the TBI population and across a wider range of ICP values has yet to be demonstrated
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