A technique for the investigation of intracranial pressure in man

Measurements of intracranial pressure have an important place in the investigation of neurological disease. Isolated estimations provide limited information, but more precise -and valuable data are obtained by monitoring intracranial pressure changes over an extended period. A number of workers have published reports describing graphic methods for recording lumbar or ventricular fluid pressures (Blackfan, Crothers, and Ganz, 1929; Carmichael, Doupe, and Williams, 1937; Antoni, 1946; Ryder, Espey, Kristoff, and Evans, 195 1; Guillaume and Janny, 195 1; Lundberg, 1960; Keegan and Evans, 1962; and others). Lundberg (1960) in his monograph 'Continuous recording and control of ventricular fluid pressure in neurosurgical practice' has published detailed recordings of ventricular fluid pressure changes in a large series of patients and has drawn attention to the characteristic pressure waves which are observed. Most of the techniques described rely upon the measurement of cerebrospinal fluid pressure in the lumbar sac or a lateral ventricle by means of a tube connected to a pressure transducer or manometer (Lundberg and others). Success requires satisfactory placement of the tube in the fluid space and maintenance of unobstructed communication with the recording apparatus. Lundberg mentions that the ventricular catheter became blocked in 17 of his cases with consequent interruption of recordings. Other workers have used small fluid-filled latex tambours inserted into the subdural space and connected by means of a tube to a pressure transducer and recorder (Hoppenstein, 1965). In our investigation we considered it essential that the following criteria should be fulfilled:-1 The method must be simple, reliable, and able to function efficiently under a wide variety of conditions for prolonged periods, either continuously or intermittently with only occasional expert supervision. 2 It must cause no significant additional discomfort or risk to the patient. 3 It must be simple to disconnect the patient from the recording apparatus so as to impose no unnecessary restriction of activities or interference with other investigations or treatment. 4 It must yield the maximum information concerning variations in intracranial pressure and other relevant phenomena. In the technique described below a pressuresensitive transducer is inserted directly into the skull. The advantages of the method are. 1 It is not dependent on cerebrospinal fluid drainage, and the technical difficulties of maintaining a free fluid communication, particularly when the ventricles are small or distorted, are avoided. 2 The transducer can be inserted at any convenient place in the skull and will record the pressure exerted by the brain against the cranium at that point (Fig. 1). 3 The risk of infection is minimal. Experience in the treatment of psychiatric disorders by multifocal leucotomy has shown that multiple intracerebral gold electrodes may be left in situ for many months without significant hazard (Crow, Cooper, and Phillips, 1961). The leads from the transducer emerging through the scalp wound are much finer than a ventricular catheter (not more than 1 mm. in diameter) and we have encountered no case of sepsis. Ps. pyocyanea was cultured from one wound swab on removal of the transducer after four and a half weeks, but the wound healed soundly without clinical evidence of infection. 4 The insertion of the pressure transducer is conveniently combined with the placement of subdural gold electrodes for monitoring phenomena such as cortical E.E.G., oxygen availability, and electrical impedance. 5 At the conclusion of recording the transducer can be removed very easily under local anaesthesia and after sterilization is available for further use. In practice the method is well tolerated, and patients have admitted no discomfort.