Intracranial Pressure: More Than a Number

Marek Czosnyka, PH.D.; Peter Smielewski, PH.D.; Ivan Timofeev, M.D.; Andrea Lavinio, M.D.; Eric Guazzo, M.D.; Peter Hutchinson, Ph.D.; John D. Pickard, F.Med.Sci.

Disclosures

Neurosurg Focus. 2007;22(5):E10 

In This Article

Abstract and Introduction

Abstract

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.

Introduction

Intracranial pressure is probably the most commonly monitored brain parameter in neurocritical care. The majority of the bedside monitors, including contemporary intraparenchymal transducer "boxes" (for ex ample, the Codman Express or Sophysa Pressio) display the mean ICP numerically or its pulse waveform with an option of condensed time trends (as with the Camino ICP Monitor or Raumedic Datalogger). This may be sufficient to guide a CPP-oriented protocol[31] or treat patients according to the Lund concept,[1,23] but much valuable information regarding complex intracranial regulatory processes is lost. What is this information? Is its clinical validity prov en or just suggested? Two generations of clinical neuroscientists have contributed to the fascinating subject of ICP waveform analysis. Lundberg[20] taught us about various slow waves of ICP and their pathological meaning. Lang fitt[18] and Lofgren and Zwetnow[19] introduced the pres sure–volume curve and the term "compensatory re serve." Other scientists[32,22] laid the foundation for the clinical testing of brain compliance. Brain insults, such as short-term increases in ICP or decreases in CPP, were used as predictors of outcome after brain trauma. The pulse waveform of ICP was then used as a source of prognostic information.[29] Is there any room for new concepts? Advances in multimodal bedside brain monitoring and data processing have made it possible to perform online, real-time analysis of the interdependence between the dynamic behaviors of var ious modalities. As information becomes more complex, it becomes notoriously difficult to detect and interpret phenomena of interest without computer bedside data analysis.[33] In this review of our own observations, we at tempt to highlight those phenomena and secondary ICP indices that may aid in the acute treatment of the severely head injured patient.

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