Sonographic Monitoring of Weaning of Cerebrospinal Fluid Drainages

Overview

As elaborated above only one study reported ultrasonographic changes of the width of the lateral ventricle during clamping of EVD/LD and indicated that ultrasound monitoring might be suitable. No firm data exists about the change of the width of the third ventricle, the diameter of the optic nerve or brain perfusion during clamping of the EVD/LD, although the width of these structures has been shown to depend on intracranial pressure. Ultrasonographic measurements of changes of the width of the third ventricle or the diameter of the optic nerve would have some advantages compared to the ultrasonographic assessments of the lateral ventricles. First, the width of the third ventricle can be measured easier and more reliable than the width of the lateral ventricles (better defined insonation plane and therefore higher repeatability of measurements) 3. Second, whereas assessments of the width of the side and third ventricles with ultrasound depend on the temporal bone windows (10 to 15% of patients have insufficient temporal bone windows), the measurement of the diameter of the optic nerve does not have this limitation and can therefore be performed in almost all patients. Hence, measurement of the diameter of the optic nerve would allow to overcome one major limitation of transcranial ultrasound. The latter limitation for transcranial ultrasound could also be minimized by the use of an ultrasound contrast agent (SonoVue®), but this was also not yet studied. The use of an ultrasound contrast agent would in addition allow to study changes of brain perfusion during clamping of EVD/LD.

Background Placement of a CSF drainage catheter (external ventricular drainage (EVD) or lumbar drainage (LD)) is a frequent neurosurgical emergency intervention. It is used in case of obstructive hydrocephalus as it can occur after e.g. intracerebral hemorrhage with intraventricular involvement, subarachnoid hemorrhage or traumatic brain injury but also in situations with reduced CSF resorption or increased CSF production (e.g. meningitis, ventriculitis). Furthermore, this technique can be used to monitor intracranial pressure. In all these situations, the EVD/LD can be used to reduce the elevated intracranial pressure during the acute phase. However, because of impairment of the Paccioni granulations by blood and its breakdown products, a continuing hydrocephalus may develop, leading to permanent necessity of CSF drainage. To evaluate the need for a permanent (implanted) drainage system (e.g. ventriculoperitoneal or ventriculoatrial shunt) attempts to clamp the EVD/LD are carried out during the subacute phase. Successful clamping is verified by absent increase of intracranial pressure, absent clinical deterioration and lack of ventricular enlargement on serial CT scans. The latter means that a first CT scan has to be performed before clamping of the drainage catheter (baseline examination) and again 24 hours after clamping of the drainage catheter. This leads to the need for repeated transportations of critically ill patients with possible harm of the patient, high costs, need for more staff and repeated exposure of the patient to radiation. Hence, a simple, repeatable, non-invasive, bedside tool for diagnosis of ventricular enlargement due to clamping of EVD/LD is strongly needed. Transcranial ultrasound has become a widely used technique mainly for measuring arterial blood flow velocities. More recently, transcranial ultrasound has been also used to assess brain tissue, brain perfusion and ventricular size. The major advantages of ultrasound are its non-invasive character, the possibility for bedside application, low costs and safety (no X-ray exposure). Some studies have tried to use transcranial ultrasound for indirect assessment of intracranial pressure. As target structures for transcranial ultrasound either the lateral ventricles, the third ventricle or the diameter of the optic nerve were used. All studies could demonstrate a correlation between the width of the lateral or third ventricle or the diameter of the optic nerve with intracranial pressure. To the investigators' knowledge, only one study assessed the change of the width of the lateral ventricles during clamping of EVD/LD. To summarize, a bedside method for assessment of changes of ventricle width/diameter of the optic nerve during clamping of EVD/LD is urgently needed and would facilitate the procedure, higher patient safety and lower costs. By now, there are some promising ultrasound methods (transcranial ultrasound with or without contrast enhancing agent to determine the width of the side and third ventricle, diameter of the optic nerve), which might substitute repeated CT scans but have not been evaluated for monitoring clamping of EVD/LD. Objective 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. Methods The study consists of two additional ultrasonographic examinations . The standard treatment of patients undergoing clamping of EVD/LD is not affected by the study. The first ultrasonographic examination is performed in parallel to the baseline CT scan (either immediately before or after the CT scan) before clamping of the EVD/LD. The second ultrasound is made 24 hours after clamping of the EVD/LD in parallel to the follow-up CT Scan (either immediately before or after the CT scan). The examinations will be made bedside in the supine position on the ward where the patient is treated.