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Morten Andresen and Marianne Juhler

Object

Current published normal values for intracranial pressure (ICP) are extrapolated from lumbar CSF pressure measurements and ICP measurements in patients treated for CSF pressure disorders. There is an emerging agreement that true normal ICP values are needed for diagnostic and therapeutic purposes. This study documents normal ICP in humans.

Methods

In this study the authors included adult patients scheduled for complete removal of a solitary, clearly demarcated, small brain tumor. The mean age of these patients was 67 years old (range 58–85 years old). Exclusion criteria were intended to create a study population with as normal brains as possible. A new telemetric ICP monitoring device was implanted at the end of surgery and monitoring was conducted 2 and 4 weeks postoperatively.

Results

In the supine position, mean ICP was 0.5 ± 4.0 mm Hg at 4 weeks postoperatively. Postural change to the standing position resulted in a decrease in mean ICP to −3.7 ± 3.8 mm Hg. These results show ICP to be considerably lower than previously estimated.

Conclusions

This study provides a preliminary reference range for normal ICP in humans. It is the first study to show that ICP in the healthy human brain decreases to negative values when assuming the upright position. If these results are later confirmed in a larger series, they might provide reference values for diagnosis and treatment in patients with CSF-related disorders. New normal values also have implications for future shunt design and the ICP target range in hydrocephalus treatment.

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Morten Andresen, Marianne Juhler and Ole Cornelius Thomsen

Object

Intracranial pressure (ICP) monitoring is used extensively in clinical practice, and as such, the accuracy of registered ICP values is paramount. Clinical observations of nonphysiological changes in ICP have called into question the accuracy of registered ICP values. Subsequently, the authors have tried to determine if the ICP monitors from major manufacturers were affected by electrostatic discharges (ESDs), if the changes were permanent or transient in nature, and if the changes were modified by the addition of different electrical appliances normally used in the neurointensive care unit environment.

Methods

The authors established a test setup in the neurointensive care unit using a large container filled with isotonic saline, creating a phantom patient. Intracranial pressure monitors were sequentially lowered into the container and subjected to a predefined test battery of ESDs.

Results

Five pressure monitors from 4 manufacturers were evaluated. Three monitors containing electrical circuitry at the tip of the transducer were all affected by ESDs. Clinically significant permanent changes in the reported ICP values for 1 pressure monitor were observed, as well as temporary deflections for 2 other monitors. The monitors had different levels of sensitivity to discharges at low voltages.

Conclusions

These results explain some of the sudden shifts in ICP noted in the clinical setting. However, a clear deflection pattern related to the addition of electrical appliances was not found. The authors recommend instituting policies for reducing the risk of subjecting patients to ESDs in the neurointensive care unit setting.

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Alexander Lilja-Cyron, Morten Andresen, Jesper Kelsen, Trine Hjorslev Andreasen, Lonnie Grove Petersen, Kåre Fugleholm and Marianne Juhler

OBJECTIVE

Decompressive craniectomy (DC) is an emergency neurosurgical procedure used in cases of severe intracranial hypertension or impending intracranial herniation. The procedure is often lifesaving, but it exposes the brain to atmospheric pressure in the subsequent rehabilitation period, which changes intracranial physiology and probably leads to complications such as hydrocephalus, hygromas, and “syndrome of the trephined.” The objective of the study was to study the effect of cranioplasty on intracranial pressure (ICP), postural ICP changes, and intracranial pulse wave amplitude (PWA).

METHODS

The authors performed a prospective observational study including patients who underwent DC during a 12-month period. Telemetric ICP sensors were implanted in all patients at the time of DC. ICP was evaluated before and after cranioplasty during weekly measurement sessions including a standardized postural change program.

RESULTS

Twelve of the 17 patients enrolled in the study had cranioplasty performed and were included in the present investigation. Their mean ICP in the supine position increased from –0.5 ± 4.8 mm Hg the week before cranioplasty to 6.3 ± 2.5 mm Hg the week after cranioplasty (p < 0.0001), whereas the mean ICP in the sitting position was unchanged (–1.2 ± 4.8 vs –1.1 ± 3.6 mm Hg, p = 0.90). The difference in ICP between the supine and sitting positions was minimal before cranioplasty (1.1 ± 1.8 mm Hg) and increased to 7.4 ± 3.6 mm Hg in the week following cranioplasty (p < 0.0001). During the succeeding 2 weeks of the follow-up period, the mean ICP in the supine and sitting positions decreased in parallel to, respectively, 4.6 ± 3.0 mm Hg (p = 0.0003) and –3.9 ± 2.7 mm Hg (p = 0.040), meaning that the postural ICP difference remained constant at around 8 mm Hg. The mean intracranial PWA increased from 0.7 ± 0.7 mm Hg to 2.9 ± 0.8 mm Hg after cranioplasty (p < 0.0001) and remained around 3 mm Hg throughout the following weeks.

CONCLUSIONS

Cranioplasty restores normal intracranial physiology regarding postural ICP changes and intracranial PWA. These findings complement those of previous investigations on cerebral blood flow and cerebral metabolism in patients after decompressive craniectomy.