Shunt settings may have little effect on intracranial pressure in hydrocephalus

1. Shunt valve settings had less of an effect on patient intracranial pressure (ICP) than previously predicted by in vitro shunt testing. 

2. Patient ICP wave amplitudes (AMPs) were never stabilized, indicating the complexity and dynamic changes of in-vivo intracranial pressure. 

Evidence Rating Level: 3 (Average)        

Study Rundown: While it is well established that intracranial pressure (ICP) is dependent on body position, measurements of ICP are generally only collected from patients in the supine(horizontal) position, and few studies have investigated shunt effectiveness in mobile hydrocephalus patients. Cardiac pulsations drive a periodic rise and fall in ICP, and stabilization of the ICP wave amplitude (AMP) is generally associated with positive patient outcome. This study measured both ICP and AMP in patients in supine and seated positions as well as while walking. Adjustable differential pressure shunts, used to prevent under or overdrainage of cerebral fluid, were implanted in all patients before such collection of ICP measurements. Patient ICP was found to be greatest in supine patients and decreased significantly when the patients were walking or sitting. Independent of body position, both ICP and AMP levels fell as the valve opening pressure setting was decreased. Surprisingly, the changes in ICP caused by varying valve setting were significantly less than those predicted by in vitro testing of the devices. The authors suggest this may be a result of the pulsatile, noisy nature of ICP. Both ICP and AMP values were dependent on valve settings. Notably, AMP stabilization was never achieved, suggesting potential need for continued evaluation of adjustable shunt settings. Technical limitations prevented calculation of pressure differences across shunt valves restricting the study’s ability to evaluate when valves opened to allow fluid drainage.

Click to read the study in Journal of Neurology, Neurosurgery and Psychiatry

Relevant Reading: Relationship between Valve Opening Pressure, Body Position, and Intracranial Pressure in Normal Pressure Hydrocephalus: Paradigm for Selection of Programmable Valve Pressure Setting

In-Depth [prospective cohort]: This study determined mean ICP and AMP values for 15 hydrocephalus patients. Prior to ICP measurements, patients received an adjustable ventriculoperitoneal shunt and intraparenchymatous ICP sensor. Measurements were collected in 10-minute segments for three body positions (supine, sitting, or walking) and four shunt valve settings (closed, or opening pressure of 13.1 mm Hg, 7.7 mm Hg, or 3.4 mm Hg). Mixed model analysis with patients set as random effect was used to evaluate the effect of body position and valve setting on ICP and AMP. When compared to that of patients in the supine position, mean patient ICP across all shunt settings was significantly lower in patients sitting (D = 11.5 mm Hg; p < 0.001) or walking (D = 10.5 mm Hg; p < 0.001). Mean ICP and AMP averaged over all body positions were dependent on shunt setting, with the closed setting driving the highest values and the lowest opening pressure setting resulting in the lowest values. The change in mean ICP values achieved by varying shunt setting from lowest to highest opening pressure was approximately 4 mm Hg in this patient study, compared to the 10 mm Hg value found in a previous bench study.

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Image: PD 

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