Bedside invasive monitoring techniques in severe brain-injured patients

Multimodality monitoring in severe head injury

PURPOSE OF REVIEW

This review describes recent advances in multimodal neuromonitoring of patients following severe head injury during the period from 2001 to 2002.

RECENT FINDINGS

Monitoring intracranial pressure is considered a standard part of therapy despite a lack of randomized studies comparing patients with and without intracranial pressure monitoring. Jugular oximetry and brain tissue oxygen pressure monitoring are being used more frequently as part of a treatment protocol. Intracerebral microdialysis, despite the widespread use as a research tool, still cannot be considered a standard in clinical monitoring. These new monitoring devices may provide useful insight into the evolution of brain injury.

SUMMARY

Technology is rapidly changing the nature of neuromonitoring. New devices are becoming available which make the monitoring truly multimodal. Studies are needed to determine how to best incorporate these new parameters into effective management protocols.

The detection of brain oedema with frequency-dependent phase shift electromagnetic induction

The spectroscopic distribution of inductive phase shift in the brain as a function of the relative volume of oedema was evaluated with theoretical and experimental methods in the frequency range 1 to 8 MHz. The theoretical study employed a simple mathematical model of electromagnetic induction in tissue and brain tissue data available from the literature to calculate the phase shift as a function of oedema in the bulk of the brain. Experimental data were generated from bulk measurements of ex vivo homogenized pig brain tissue mixed with various volumes of physiological saline in a volume sample typical of the human brain. There is good agreement between the analytical and the experimental results. Detectable changes in phase shift begin from a frequency of about 3 MHz to 4 MHz in the tested compositions and volume. The phase shift increases with frequency and fluid content. The results suggest that measuring phase shift in the bulk of the brain has the potential for becoming a robust means for non-contact detection of oedema in the brain.

Advances in ICP monitoring techniques

With the advent of newer devices for measuring intracranial pressure (ICP) and cerebral metabolism, more alternatives continue to rise aiming to control ICP. This manuscript presents a proposed analysis of different ICP monitoring devices in order to make appropriate selection of them in our clinical setting including general and pediatric applications. A systematic review of the literature was made analyzing the technical advances in ICP monitoring. The recent in vitro and in vivo tests as well as mathematical/computer models were reviewed. Practical applications of principles were discussed and compared based on the mode of pressure transformation. A ventricular catheter connected to an external strain gauge transducer or catheter tip pressure transducer device is considered to be the most accurate method of monitoring ICP and enables therapeutic CSF drainage. The significant infections or hemorrhage associated with ICP devices causing patients morbidity are clinically rare and should not deter the decision to monitor ICP. Parenchymal catheter tip pressure transducer devices are advantageous when ventricular ICP cannot be obtained or if there is an obstruction in the fluid couple, though they have the potential for significant measurement differences and drift due to the inability to recalibrate. Subarachnoid or subdural fluid-coupled devices and epidural ICP devices are currently less accurate. With an increasing miniaturization of the transducers, fiberoptic systems have been developed, however, there is a problem of measurement accuracy during the period of patient monitoring and external calibration should be performed frequently to ensure constant accuracy. Ventriculostomies continue to have a pivotal role in ICP control. With a rational understanding of the applications and limitations of the different ICP monitoring devices, the outcome for critically ill neurological patients is optimized.