External Ventricular Drain Placement Stealth Study

External ventricular drain (EVD) placement is performed very often in neurosurgical practices. EVD's are used most commonly to monitor intracranial pressure and divert cerebrospinal fluid (CSF) in patients with increased intracranial pressures. Pathologies where EVDs are most frequently needed include hydrocephalus, malignancy, and/or trauma. EVD's are most commonly placed at the bedside using external anatomical landmarks to guide the catheter into the frontal horn of the ipsilateral lateral ventricle. EVDs are often placed due to acute neurological compromise and require timely insertion. This can increase the associated risk and result in complications.

Accurate catheter placement is essential to achieving effective external CSF drainage without complications or occlusion/failure of the catheter. Catheter placement is most commonly performed via a freehand approach using external anatomical landmarks to help identify the location of the lateral ventricle within the brain without the aid of imaging. Proper identification of the ventricles on pre-procedure imaging, surgeon skill, and estimation of pathologic perturbations to the normal location of the ventricles all factor into the success of catheter placement. Multiple passes are often required. The accuracy rate from the freehand technique has been reported to range from 40 to 98 percent. A very basic grading scale has been developed to assess placement but does not include items such as the number of passes until successful placement and presence of post placement hemorrhage or other neurological complications. An increased number of passes increases the risk of post placement hemorrhage and may damage the brain. Hemorrhage has been reported to occur after catheter placement at rates ranging from 0.2 to 41 percent.

Current methods for EVD placement do not compensate for superficial brain vessels or pathology that may alter the intracranial anatomy such as trauma, hemorrhage, or mass lesions. Some studies have attempted to use CTA imaging to identify intracranial vessels in an attempt to avoid them during placement.

Image guidance is a tool used very commonly for placement of EVD's and shunts in the operating room. AxiEM Stealth is a noninvasive image localization modality that registers a CT or MRI to the individual patients facial and scalp anatomy. A probe can then be used to identify, in real-time, the underlying anatomy and trajectories. This imaging guidance may improve the accuracy of EVD placement.

This study will compare the current standard of care of freehand placement of bedside external ventricular catheters to the placement of EVD catheters with AxiEM Stealth image guidance. Accuracy of the tip of the catheter, occurrence of post-placement hemorrhage, the number of passes required for CSF flow, ventricle diameter, catheter clogging/failure, time required for placement, patient demographics and other secondary outcome measures such as Glasgow Outcome Scale (GOS) and Modified Rankin Score (MRS) will be collected. The hypothesis is that image guided EVD catheter placement will improve accuracy, decrease the number of brain transgressions, and decrease complications of EVD placement.

What makes up an external ventricular drain and how does it work? An external ventricular drain (EVD) is comprised of a catheter, drainage tubing, and a collection system. Once the catheter is in the ventricular system, it works by measuring the intracranial pressure via a transducer and drains excess CSF from the ventricular system to ensure pressures does not exceed a set threshold. Normal intracranial pressures range from about 5-20 mmHg and are usually around 10mmHg. The EVD system can be set at a certain level and when the intracranial pressures rise above that level, CSF drains out the catheter into the collecting system. The EVD system can be raised or lowered to create different intracranial pressure thresholds and keep intracranial pressures controlled in patients that have a pathology, such as cerebral swelling or ventricular obstruction, leading to increased pressures.

What is the current technique used to place an EVD? A sterile field is prepared about 10-12 centimeters posterior to the eye (either right or left as clinically indicated) and about 2-3 cm lateral to the midline of the skull. This point should be about 1 cm anterior to the coronal suture. An incision is made at this point and a burr hole is created using a hand drill. The EVD catheter is prepared using a stylet to help with movement through the brain parenchyma. The catheter is advanced in a trajectory perpendicular to the skull, which results in a direction that is towards the ipsilateral medial canthus and ipsilateral tragus which are other landmarks that can be used. The catheter is advanced to 5-6 cm and the stylet is removed to assess for CSF flow. If CSF flow is not appreciated, then the catheter is passed softly for about 1 more centimeter. If CSF flow is still not appreciated, the catheter is removed and the stylet replaced for another attempt. If unsuccessful after 3 attempts, the catheter can be left in place and a head CT can be done to assess the adjustments that need to be made. This can often take up to 10 passes or more if there is significant brain shift due to mass effect or aberrant anatomy. Once CSF flow is obtained, the catheter is tunneled posteriorly and anchored to the skin with a stitch. The incision is then closed and the catheter is connected to the drainage tubing of the collection system. The presence of CSF drainage is checked at multiple points during closure to ensure that the catheter remains in good position.

How does Axiem Stealth work as an image guidance system and how is it used for EVD placement? The first step for using the image guidance system is to upload the most recent (since admission or within 6 hours from bleeding) head CT or MRI into the Stealth station that has been obtained since admission. The Axiem Stealth imaging guidance system uses a probe (AxiEM Registration Probe) and a side mount emitter (AxiEM Side Mount Emitter) to register the patient's head in relation to the probe. A trajectory (entry point and target) is then planned. This registration process takes an estimated 5-15 minutes to perform. A separate stylet (StealthStation EM Stylet) is designed specifically for the catheter and slides down the center of the catheter. A burr-hole is created at the predefined precise location and the catheter is passed to the target under electromagnetic guidance.

Relevance of this research:

The novelty of this study is to investigate whether using image guidance technology can improve EVD catheter placement. Image guidance is used very commonly for EVD and shunt placement in the operating room with excellent accuracy and precision. The hypothesis is that using this same workflow at the bedside will improve accuracy; decrease the number of passes needed for a successful placement, decrease the number of post-placement hemorrhagic events, and help improve the effectiveness of the catheter as well as patient outcomes.