Is there a reasonable differential indication for different hydrocephalus shunt systems?

Abstract

We tested various shunt systems for pressure/flow characteristics and long-term reliability. In addition, we used a model to simulate activities of daily life postural changes, blood and airway pressure changes and their impact on CSF pressure and flow through various ventriculo-peritoneal shunt systems. In the recumbent position, the changes in flow rate and CSF pressure depended on the valve resistance. Various valves showed deviations from the pressure/flow characteristics claimed for, them and proved to be unreliable during long-term perfusion. The flow rate increased in the head-up position. Negative intracranial CSF pressure was due to the continued flow through the shunt system afforded by the siphon effect. The siphon effect was so marked in the upright position that valves of various kinds, and with various resistances did not make any significant difference in the resulting intracranial pressure (ICP). The shunt systems, however, differed in the maximum flow rate in the upright position, leading to a different steep fall in ICP following elevation of the body. Ball-and-spring valves had the highest flow rates (>500 ml/h), leading to negative ICP within seconds. Diaphragm valves, and especially the self-adjusting diaphragm valve, demonstrated a slower drop in ICP, taking several, minutes to reach negative ICP. ASD and SCD, however, did prevent any siphoning effects, leading to an ICP within the corresponding valve opening/closing pressure range. Our results demonstrate that in most patients there is no significant difference in various different shunting systems as long as the patient, is mobile. Different pressure values, however, may be important in bed-ridden patients with no postural hydrostatic CSF pressure changes. The difference in the drop in ICP during postural changes may be an important factor in a certain group of patients who are prone to negative pressure-dependent complications, e.g., slit-ventricle syndrome, subdural hematoma and hygroma. More important than the development of sophisticated new shunt systems is the maintenance, of longterm durability and the ability to rely on the valves' characteristics.