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  • Author or Editor: Ela Chakkarapani x
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Kristian Aquilina, Marianne Thoresen, Ela Chakkarapani, Ian K. Pople, Hugh B. Coakham and Richard J. Edwards

Object

Intracranial pressure (ICP) monitors are currently based on fluid-filled, strain gauge, or fiberoptic technology. Capacitive sensors have minimal zero drift and energy requirements, allowing long-term implantation and telemetric interrogation; their application to neurosurgery has only occasionally been reported. The aim of this study was to undertake a preliminary in vitro and in vivo evaluation of a capacitive telemetric implantable ICP monitor.

Methods

Four devices were tested in air- and saline-filled pressure chambers; long-term capacitance-pressure curves were obtained. Devices implanted in a gel phantom and in a piglet were placed in a 3-T MR unit to evaluate MR compatibility. Four devices were implanted in a piglet neonatal hydrocephalus model; output was compared with ICP obtained through fluid-filled transduction and a strain-gauge ICP monitor.

Results

The capacitance-pressure relationship was constant over 4 weeks, suggesting minimal zero drift during this period. There were no temperature changes around the monitor. Signal loss at the sensor was minimal in both the phantom and the piglet. Over 114,000 measurements were obtained; the difference between mean capacitive ICP and fluid-transduced ICP was 1.8 ± 1.42 mm Hg. The correlation between ICP from the capacitive sensor and fluid-filled transducer (r = 0.97, p < 0.0001) or strain-gauge monitor (r = 0.99, p < 0.0001) was excellent. In vivo monitoring was restricted to 48 hours due to problems with robustness in the clinical environment.

Conclusions

This preliminary study demonstrates minimal long-term zero drift in vitro, good MR compatibility, and good correlation with other methods of ICP monitoring in vivo in the short term. Further long-term in vivo study is required.

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Kristian Aquilina, Ela Chakkarapani and Marianne Thoresen

Object

The optimal management of neonatal intraventricular hemorrhage (IVH) and posthemorrhagic ventricular dilation is challenging. The importance of early treatment has been demonstrated in a recent randomized study, involving early ventricular irrigation and drainage, which showed significant cognitive improvement at 2 years. The objective of this study was to define the changes in CSF absorption capacity over time in a neonatal piglet model of IVH.

Methods

Ten piglets (postnatal age 9–22 hours) underwent intraventricular injection of homologous blood. A ventricular access device was inserted 7–10 days later. Ventricular dilation was measured by ultrasonography. Serial constant flow infusion studies were performed through the access device from Week 2 to Week 8.

Results

Seven piglets survived long term, 43–60 days, and developed ventricular dilation; this reached a maximum by Week 6. There was no significant difference in baseline intracranial pressure throughout this period. The resistance to CSF outflow, Rout, increased from 63.5 mm Hg/ml/min in Week 2 to 118 mm Hg/ml/min in Week 4. Although Rout decreased after Week 5, the ventriculomegaly persisted.

Conclusions

In this neonatal piglet model, reduction in CSF absorptive capacity occurs early after IVH and accompanies progressive and irreversible ventriculomegaly. This suggests that early treatment of premature neonates with IVH is desirable.