The baric probe: a novel long-term implantable intracranial pressure monitor with ultrasound-based interrogation

Technical note

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  • 1 Departments of Neurological, Surgery
  • | 2 Pediatrics,
  • | 3 Mechanical Engineering and Materials Science, and
  • | 4 Computer Science and Engineering;
  • | 5 Division of Comparative Medicine; and
  • | 6 Center for Innovation in Neuroscience and Technology, Washington University in St. Louis, Missouri; and
  • | 7 Department of Neurological Surgery, Emory University School of Medicine, Atlanta, Georgia
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Object

Prompt diagnosis of shunt malfunction is critical in preventing neurological morbidity and death in individuals with hydrocephalus; however, diagnostic methods for this condition remain limited. For several decades, investigators have sought a long-term, implantable intracranial pressure (ICP) monitor to assist in the diagnosis of shunt malfunction, but efforts have been impeded by device complexity, marked measurement drift, and limited instrumentation lifespan. In the current report, the authors introduce an entirely novel, simple, compressible gas design that addresses each of these problems.

Methods

The device described herein, termed the “baric probe,” consists of a subdural fluid bladder and multichannel indicator that monitors the position of an air-fluid interface (AFI). A handheld ultrasound probe is used to interrogate the baric probe in vivo, permitting noninvasive ICP determination. To assess the function of device prototypes, ex vivo experiments were conducted using a water column, and short- and long-term in vivo experiments were performed using a porcine model with concurrent measurements of ICP via a fiberoptic monitor.

Results

Following a toe region of approximately 2 cm H2O, the baric probe's AFI demonstrated a predictable linear relationship to ICP in both ex vivo and in vivo models. After a 2-week implantation of the device, this linear relationship remained robust and reproducible. Further, changes in ICP were observed with the baric probe, on average, 3 seconds in advance of the fiberoptic ICP monitor reading.

Conclusions

The authors demonstrate “proof-of-concept” and feasibility for the baric probe, a long-term implantable ICP monitor designed to facilitate the prompt and accurate diagnosis of shunt malfunction. The baric probe showed a consistent linear relationship between ICP and the device's AFI in ex vivo and short- and long-term in vivo models. With a low per-unit cost, a reduced need for radiography or CT, and an indicator that can be read with a handheld ultrasound probe that interfaces with any smart phone, the baric probe promises to simplify the care of patients with shunt-treated hydrocephalus throughout both the developed and the developing world.

Abbreviations used in this paper:

AFI = air-fluid interface; ICP = intracranial pressure.

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Contributor Notes

Address correspondence to: David D. Limbrick Jr., M.D., Ph.D., Department of Neurological Surgery, Washington University School of Medicine, St. Louis Children's Hospital, One Children's Place, Suite 4S20, St. Louis, Missouri 63110-1077. email: limbrickd@wudosis.wustl.edu.

Please include this information when citing this paper: published online September 28, 2012; DOI: 10.3171/2012.8.PEDS11565.

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