A Comparison of the Amount of Cerebrospinal Fluid formed in 24 hours with the Amount Delivered through the Holter Valve

THIS paper was written as it had been noted that some cases of progressive hydrocephalus were not arrested by the insertion of a Holter valve, but on checking the valve assembly it seemed to be in full working order. Mr. Holter and I thought there was a possibility of restriction of the valve at the time of sterilisation as it has to be sterilised in fluid contained in a polythene packet, then cooled and the packet sealed. Mr. Holter then prepared a chart showing the rates of flow of various pressures of water in relation to the 10 mm. subdural valve, the 25 mm. medium valve and the 42 mm. normal valve. He was able to show that a medium valve at 170 mm. pressure delivers about 290 ml. of fluid in 24 hours, and at 150 mm. pressure about 240 ml. At 70 mm. pressure it only delivers 43 ml. This means that a drop of pressure of 100 mm. will reduce the rate of delivery from 290 ml. down to 43 ml. in a 24-hour period. Before insertion of a valve it should be tested for restriction. An 18-in. length of polythene tubing is attached to the inlet end of the valve, tubing and valve are pumped full of water, the tubing is then held up with the valve in the dependent position and the fluid meniscus in the tubing should drop 9-in. within two minutes. If this does not occur the valve has to be thoroughly syringed through and re-tested. Following the preparation of Mr. Holter's chart I then carried out some simple methods to attempt to establish how much cerebrospinal fluid a hydro-cephalic infant formed in 24 hours. The first procedure was to set up 24-hour ventricular drainage against the child's own ventricular pressure. The second procedure was to insert the valve and measure the outflow of cerebrospinal fluid from the exteriorised venous catheter in 24 hours at the child's own ventricular pressure. The third procedure was to measure the outflow through the valve against the child's own ventricular pressure. It was interesting to note that in the first procedure, where there had been a sudden drop in the infant's original ventricular pressure, the ventricular drainage was small. This meant that the infant had gone into a quiescent phase, but 24 hours later when a valve was inserted and pressures had risen to 140 mm. and 160 mm., the amount of cerebrospinal fluid collected in 24 hours came to 213 ml. and 291 ml. This fitted in with Mr. Holter's chart. Where the original ventricular and drainage pressures are the same, the rate of ventricular drainage remains high, even when it is drained against its own ventricular pressure. This means that patients with a high ventricular pressure will continue to form cerebrospinal fluid. In the third procedure, it was noted that when the drainage through the valve system at 0 mm. pressure was raised to the infant's own ventricular pressure, formation of cerebrospinal fluid almost stopped. Holter has shown us that the rate of flow through the valve is dependent on the head of pressure. A pressure of 70 mm. through a medium valve will form less than two drops in two minutes; flow has, therefore, almost stopped. There are wide fluctuations of pressure in progressive hydrocephalus and a sudden drop from a high pressure will cause temporary arrest of formation of cerebrospinal fluid. When the balance of ventricular pressure is restored, the rate of flow through the valve corresponds to Holter's findings. If the peripheral resistance to the outflow from the valve is raised there is a marked drop in output, so an investigation of pressures in the transverse sinus, right atrium and the right ligated internal jugular vein is being carried out. Where the original ventricular pressure is high and drainage has been established for a long period of time with a continuing high pressure the output of cerebrospinal fluid is little affected by raising the peripheral resistance, even up to 200 mm. pressure. This may be one form of natural arrest and in such cases I do not find that insertion of a valve reduces the pressure.