New concept for the pressure setting of a programmable pressure valve and measurement of in vivo shunt flow performed using a microflowmeter - Technical note

The aim of this study was to establish a standard method for determining th e pressure setting of the Codman Hakim valve (CHV) in patients with hydroce phalus. The authors' investigation was twofold. It focused on: 1) the relationships among CHV setting, intracranial pressure (ICP), intraabdominal pressure (I AP), hydrostatic pressure (HP), and perfusion pressure (PP); and 2) the shu nt flow in 18 patients with normal-pressure hydrocephalus. With the patient in a sitting position, the pressure environment around the ventriculoperitoneal shunt stabilized when PP became equal to the CHV sett ing. The lower the CHV setting, the lower the ICP obtained in patients in a sitting position (ICPsit) settled. This indicated the possibility of calcu lating the CHV setting by the equation CHV setting = HP + ideal ICPsit - IA P, where the ideal ICPsit was estimated to be between -70 and - 140 mm H2O. The CHV setting was individually determined for 18 patients by using this method. The ICPsit was controlled at a level equal to the estimated ICPsit in most cases, which supported the rationality of our concept. Shunt flow w as intermittent or very low when the patient assumed a supine position and between 200 and 600 mu l/minute when the patient was seated. Determining the CHV setting by using the equation CHV setting = HP + ideal ICPsit - IAP was found to be useful when directly measuring HP and IAP in p atients and estimating the ideal ICPsit to be between -70 and - 140 mm H2O. Postoperative shunt control performed using this method was satisfactory, and shunt complications and the number of CHV resettings were lower than in those published in previous reports. Shunt-flow measurement performed in vivo and in real time by using a microf lowmeter should be useful not only in testing the functioning of shunt syst ems, but also in clarifying the pathophysiology of hydrocephalus.