Clinical evaluation of two methods of subdural pressure monitoring.

Recordings from two different types of subdural pressure monitor with simultaneous intraventricular pressure (IVP) tracings are compared in 20 head-injured patients. In the first 10 patients a fluid-filled catheter was placed subdurally and connected to an external transducer, and in the second 10 the Gaeltec model ICT/b solid state miniature transducer was used. The latter system has the advantage that both zero and calibration checks can be carried out after insertion. Only 44% of the fluid-filled catheter readings corresponded with IVP in series of 10-mm Hg ranges, while 53% of readings were lower; this tendency was more marked at higher pressures. With the Gaeltec transducer, 72% of subdural pressure readings corresponded with IVP, while only 9% were lower and 19% were higher than IVP. The differences may have been due to technical causes or to true pressure differentials. The subdural catheter appears too unreliable for routine clinical use, but the Gaeltec transducer may be a satisfactory alternative to ventricular pressure monitoring.