The investigators hypothesize that clamping of EVD/LD can be monitored using repeated bedside ultrasound examinations instead of repeated CT scans. The purpose of this study is to investigate if a multimodal approach consisting of ultrasonographic determination of changes of the width of the third and the side ventricles as well as the diameter of the optic nerve can be used to screen for ventricle enlargement during clamping of EVD/LD. To this end, the investigators will compare a classifier based on ultrasound with the clinical decision based on CT.