the skull this may involve a bolt as described in the above cited u s pat no 4 903 707 or secured by other fixing means as indicated in fig3 b referring to this latter figure it can be seen that the catheter 21 is fixed to the patient 39 s head by securing means 14 passes under the scalp in contact with the skull 15 and then through an opening in the skull and brain 16 to reach a brain ventricle 17 the small size and flexibility of the catheter about 2 3 mm diameter facilitates introduction of the catheter the distal tip of the catheter is provided with holes to permit flow of csf therethrough and around the tip of the probe which is also located within the cerebral ventricle 16 patients admitted to hospital following brain trauma resulting in severe brain injury gcs u2266 8 were included in the study a u2018 paratrend 7 u2019 sensor measuring ph pco 2 and po 2 was advanced into a ventriculostomy sensor data was stored into a computer and transferred to a spreadsheet ph pco 2 po 2 1cp cpp patent manipulation and outcome were monitored six patients were excluded due to technical difficulties in obtaining and recording data early in the study four patients were found to have initial ph in the range 7 15 to 7 22 but had progressive csf acidemia over the next 24 to 48 hours all progressed to herniation and brain death clinical evidence of brain death occurred as the ph.