Intracranial pressure monitoring

Advances in Intracranial Pressure Monitoring and Its Significance in Managing Traumatic Brain Injury

Intracranial pressure (ICP) measurements are essential in evaluation and treatment of neurological disorders such as subarachnoid and intracerebral hemorrhage, ischemic stroke, hydrocephalus, meningitis/encephalitis, and traumatic brain injury (TBI). The techniques of ICP monitoring have evolved from invasive to non-invasive-with both limitations and advantages. Some limitations of the invasive methods include short-term monitoring, risk of infection, restricted mobility of the subject, etc. The invasiveness of a method limits the frequency of ICP evaluation in neurological conditions like hydrocephalus, thus hampering the long-term care of patients with compromised ICP. Thus, there has been substantial interest in developing noninvasive techniques for assessment of ICP. Several approaches were reported, although none seem to provide a complete solution due to inaccuracy. ICP measurements are fundamental for immediate care of TBI patients in the acute stages of severe TBI injury. In severe TBI, elevated ICP is associated with mortality or poor clinical outcome. ICP monitoring in conjunction with other neurological monitoring can aid in understanding the pathophysiology of brain damage. This review article presents: (a) the significance of ICP monitoring; (b) ICP monitoring methods (invasive and non-invasive); and (c) the role of ICP monitoring in the management of brain damage, especially TBI.

Performance characteristics of a new generation pressure microsensor for physiologic applications

A next generation fiber-optic microsensor based on the extrinsic Fabry-Perot interferometric (EFPI) technique has been developed for pressure measurements. The basic physics governing the operation of these sensors makes them relatively tolerant or immune to the effects of high-temperature, high-EMI, and highly-corrosive environments. This pressure microsensor represents a significant improvement in size and performance over previous generation sensors. To achieve the desired overall size and sensitivity, numerical modeling of diaphragm deflection was incorporated in the design, with the desired dimensions and calculated material properties. With an outer diameter of approximately 250 microm, a dynamic operating range of over 250 mmHg, and a sampling frequency of 960 Hz, this sensor is ideal for the minimally invasive measurement of physiologic pressures and incorporation in catheter-based instrumentation. Nine individual sensors were calibrated and characterized by comparing the output to a U.S. National Institute of Standards and Technology (NIST) Traceable reference pressure over the range of 0-250 mmHg. The microsensor performance demonstrated accuracy of better than 2% full-scale output, and repeatability, and hysteresis of better than 1% full-scale output. Additionally, fatigue effects on five additional sensors were 0.25% full-scale output after over 10,000 pressure cycles.

Associations between intracranial pressure, intraocular pressure and mean arterial pressure in patients with traumatic and non-traumatic brain injuries

INTRODUCTION

Anatomical proximity of the eye and the intracranial space is a fact but the existence of physiological and pathophysiological relationships between them is elusive. The objective of this study was to explore anatomical and pathophysiological interactions between the eye and the intracranial space and to assess clinical utility of intraocular pressure measurement in estimation of intracranial pressure in patients with brain injuries and to discover how haemodynamic instability could influence these interactions. Controversy surrounds the recent literature concerning this problem and the consensus has not been achieved.

MATERIALS AND METHODS

We evaluated the correlation between intracranial pressure and intraocular pressure, intracranial pressure and mean arterial pressure, intraocular pressure and mean arterial pressure in 40 patients with brain injuries initially comatose, admitted to our hospital. All patients required the intracranial pressure monitoring on clinical grounds. Simultaneous recordings of intracranial pressure, intraocular pressure and mean arterial pressure were performed.

RESULTS

We calculated both the linear correlation coefficient and the Spearman rank-order correlation coefficient for all three relations. We found significant correlation between intraocular pressure and mean arterial pressure in 63% of the tested population. When the power of the test was increased, by considering only patients with 11 or more observations, this ratio increased to 76%. However, the correlation between intraocular pressure and intracranial pressure, as well as, between intracranial pressure and mean arterial pressure was not significant.

CONCLUSIONS

There is no anatomical and pathophysiological basis for the statement that intraocular pressure can be used as an indirect estimator of intracranial pressure.

Noninvasive measurement of intracranial pressure: is it possible?

BACKGROUND

Some publications suggest a strong correlation between the intracranial pressure and the intraocular pressure. Other studies claim no correlation between these two physiologic variables. Our aim was to study whether the tonometry could be a useful method to evaluate intracranial pressure in patients with suspected intracranial abnormality.

METHODS

We evaluated the correlation between the intracranial pressure and the intraocular pressure, the intracranial pressure and the mean arterial pressure, and the intraocular pressure and the mean arterial pressure in 22 patients, initially comatose, who were admitted to our hospital. All patients required the intracranial pressure monitoring on clinical grounds. Simultaneous measurements were performed and recorded.

RESULTS

We calculated both the linear correlation coefficient and the Spearman rank-order correlation coefficient. We found significant correlation between the intraocular pressure and the mean arterial pressure in 12 patients; however, significant correlation between the intraocular pressure and the intracranial pressure was found in only 2 patients.

CONCLUSION

Tonometry is not an appropriate method for the assessment of intracranial pressure increases.