Ventriculostomy and Spinal Fluid Drainage

Cerebral Spinal Fluid Physiology

• CSF is mainly produced by the choroid plexuses in the lateral, third, and fourth ventricles. Approximately 500-600 mL of CSF is produced in an adult daily, and the circulating CSF volume in an adult typically ranges between 140 mL to 180 mL.¹ CSF travels from the third ventricle via the interventricular foramen into the fourth ventricle via the aqueduct of Sylvius into the subarachnoid space.
• The relationship between ICP, cerebral blood flow (CBF), and brain metabolism is crucial for maintaining normal brain function and preventing brain ischemia and metabolic derangements during neuroanesthesia. ICP is defined as the pressure within the cranial cavity, which is a fixed space within the rigid skull.
• The Monro-Kellie doctrine describes that the intracranial space is fixed in volume, consisting of approximately 80% brain tissue, 10% blood, and 10% CSF. If one of the components of the intracranial space increases, another component must decrease to compensate.
• A normal ICP in adults ranges from 8-15 mmHg. Various factors influence ICP, including body position, systemic blood pressure, and arterial gases, as pictured in the table below.²

• Elevated ICP can lead to several physiological dysfunctions, including Cushing’s phenomenon (hypertension, bradycardia, and widened pulse pressure followed by Cheyne-Stokes respiration, hypotension, and respiratory and/or cardiac compromise), cerebral edema, brain herniation, and compromised CBF autoregulation.
• Compromised CBF autoregulation occurs when increased ICP impairs the brain’s ability to regulate its blood flow. As ICP rises, cerebral perfusion pressure becomes more dependent on the balance between blood pressure and ICP.
• Please see the OA summary on elevated ICPs for more details. Link
• Due to this, it may be necessary to consider increasing mean arterial pressure (MAP) or draining CSF to allow for improved CPP.³

• Despite variations in CPP, the body uses CBF autoregulation to maintain stable blood flow. CBF autoregulation functions when MAP is between 50-150 mmHg. However, many circumstances encountered in neurocritical such as stroke, hypertension, brain trauma and intracranial masses, lead to unreliable autoregulation. CBF is also affected by many chemical changes in the body including oxygen level in arterial blood, carbon dioxide, pH, potassium and adenosine.

CSF Drainage Devices and Indications

Introduction

• External ventricular drains and lumbar drains (LDs) are temporary tools to both divert CSF and measure CSF pressure.^5-7 EVDs specifically are used for ICP monitoring in traumatic brain injuries, aneurysmal subarachnoid hemorrhage, acute ischemic cerebellar stroke with decompressive craniectomy, intracranial hemorrhage, intraventricular hemorrhage, facilitation of intraoperative brain relaxation, and malfunctioning or infected ventriculoperitoneal shunts.
• LDs are used for spinal cord protection during thoracic aortic repair, for active CSF leaks, for those at risk for CSF leaks due to skull base procedures, and to facilitate intraoperative brain relaxation.

Insertion of EVDs and LDs

• EVDs are placed in the lateral ventricles of the brain, while LDs are placed into the subarachnoid space. The placement of EVDs may be done emergently in a non-OR setting, such as the bedside.
• LDs may be placed preoperatively or under general anesthesia. The placement of a LD is completed using a 14 G Tuohy needle inserted in the L3-L5 level and advanced into the intrathecal space. A catheter is left in place and connected to a pressure monitoring and collection system.
• Contraindications to the placement of an EVD or LD include infection at the site of insertion or concerns regarding coagulation.

Anesthetic Considerations: Monitoring, Management and Complications

Monitoring

• A thorough understanding of the mechanism of drainage devices is essential for intraoperative management of patients with devices in place to prevent overdrainage and ensure ideal brain perfusion.
• It is important to note baseline characteristics of a patient’s existing EVD or LD system including the color and consistency of CSF. The anesthesia provider should also ensure that EVDs are leveled at the external auditory meatus and LDs are leveled at the level of the right atrium or lumbar catheter insertion site.
• Continuous ICP waveforms can be a useful tool for monitoring for cerebral dysfunction. The ICP waveform is composed of P1 (percussion wave), P2 (tidal wave), and P3 (dicrotic wave). The P1 wave correlates with arterial pressure from the choroid plexus and is the sharpest wave. The next waveform is P2 which correlates to compliance and is shorter than P1. An abnormal P2 wave indicates poor compliance. The third wave, P3, corresponds aortic valve closure.

Management

• It is important to closely monitor CSF drainage volume to prevent overdrainage and simulate normal hourly CSF production and volume found in the ventricular system under physiologic conditions (10-20 mL/h of drainage).
• Management of EVDs also involves deciding whether to “continually monitor” versus “continually drain.” An open EVD refers to an EVD that is continuously draining and intermittently closed for monitoring. A monitor EVD is continuously monitoring and is intermittently closed to drain. Choosing a mode of EVD management is dependent on the indication for the drain and the specific clinical picture.

Safety Considerations and Complications

• There are several important safety considerations when managing EVDs/LDs to prevent inaccurate measurements and minimize the risk of patient complications.
• A critical safety consideration is patient positioning intraoperatively. Changes in the position of the device relative to the patient must be recognized and addressed to ensure accuracy of measurements and prevent under or over-drainage. While patient position is being changed, especially during movement between beds and prone positioning, the drain should be clamped, if possible.
• Infection prevention is also important in the management of EVD/LD. The drainage system should be a closed system that remains sterile. Events such as drain disconnections warrant replacement of the system with new, sterile components distal to the disconnection.
• Overdrainage of CSF is a dangerous complication of CSF drainage devices. Drainage of large volumes of CSF in a short time period can lead to collapse of ventricles, which causes shrinking of cerebral hemispheres and can result in tension on bridging veins and consequently acute subdural hematomas. If patients with an unsecured aneurysm are subject to overdrainage, they are at risk for re-bleeding. The most common scenario for inadvertent overdrainage of CSF is changes in patient position without adjusting the position of the drain, which is why clamping of the drain during position changes and transportation is recommended.
• Lastly, accidental injection of medications into EVD or LD should be avoided to prevent intrathecal administration of medications that may lead to devastating consequences. Since EVD tubing often has a 3-way stopcock, precautions should be taken to avoid inadvertent injection into tubing by judiciously labeling tubing and using color-coded caps.