ICP monitoring.

Within the last two decades, the measurement of intracranial pressure (ICP) advanced from basic research to a useful method in clinical practice. The recording of ICP in clinical diagnosis and therapy requires the knowledge of physical, anatomical and pathophysiological fundamentals, of the different measurement principles and of typical, pathognomonic intracranial pressure patterns. This data will be described in this article. The ICP, and its effects, are based on the anatomy of the almost closed rigid skull which is divided into three "compartments" by pressure-resistent septa (falx, tentorium), and which opens into the spinal dura cavity as a 4th compartment. The pressure is distributed by the CSF, whereby hydrostatic laws must be considered. The brain itself is visco-elastic, and its physical characteristics change in pathological conditions. The pathophysiological effects of intracranial hypertension must be divided into generalized pressure effects and directed pressure actions. The generalized pressure effects are caused by the disturbance of the cerebral blood flow (CBF); their understanding requires the knowledge of the characteristic Pressure-Volume (P/V)-Diagram of the craniospinal space, which can be described by mathematical approximations. The directed actions of an elevated ICP are based on pressure gradients (unequal pressure distribution), which are produced by more rapidly growing local intracranial lesions. These pressure differences cause cerebral mass movements with brain stem incarceration, whereby the "pressure = force per area" - rule must be considered. These anatomical and functional basics are of great importance for the measurement technique; for reliability and safety of ICP registration, the elastic forces of the dura and the brain, the pressure distribution as well as the operative procedure and invasivity of the measurement technique have to be regarded. For clinical routine, less invasive methods using miniaturized transducers for epi- or subdural implantation are favorized above the registration of ventricular pressure, which, however, has its special indications. These problems will be described. Besides a registration of the spontaneous ICP fluctuations, a quantitative determination of the P/V-diagram (compliance, elastance, PVI) and of parameters of the CSF dynamics (resistance, CSF production, Pss) may be useful in clinical practice. In diagnosis, invasive methods with artificial volume load may be used, the techniques will be explained.(ABSTRACT TRUNCATED AT 400 WORDS)