[The changes of intracranial pressure after shunt surgery: measurements of pre- and postshunt ventricular fluid pressure with an implanted telemetric ICP sensor].

The changes of intracranial pressure (ICP) after shunt surgery are not fully known. We measured ventricular fluid pressure (VFP) in 10 hydrocephalic patients before and after ventriculoperitoneal shunts. VFP was monitored with an implanted telemetric ICP sensor placed in the shunt system equipped with an on-off valve. Recordings with the valve closed were used as preshunt VFP measurements. In serial montorings, two patterns of VFP changes were recognized. One was an immediate decrease of VFP to a steady state after the surgery. The other was a gradual decrease to constant level within several days. After reaching steady states, postshunt VFP showed around OmmHg in the supine position in a half of the patients. Head elevation (20 - 60 degrees) allowed VFP to decrease to -10(-)-25 mmHg in 9 out of 10 patients. These measurements were irrespective of the pressure range of peritoneal catheters. Changes of postshunt VFP seemed to be non-physiological, despite the improvement of symptoms brought about by the surgery. B-wave seen frequently before surgery disappeared in all but two patients. There were two types of shunt malfunction found in follow-up periods. Hypofunctions caused by a disconnection of the peritoneal catheter from the reservoir, and an intraperitoneal cyst were detected by VFP monitoring. Overdrainage of cerebrospinal fluid (CSF), however, was not disclosed by this monitoring. From these results, this ICP sensor was considered to be useful to know the perioperative VFP changes in hydrocephalic patients. And the pathogenesis of B-wave was strongly suspected to be attributable to the disturbance of CSF circulation.