A ventriculostomy is a temporary neurosurgical procedure used to manage pressure inside the brain. It involves placing a thin, flexible tube, known as an external ventricular drain (EVD), directly into one of the brain’s fluid-filled cavities, called ventricles. This catheter connects to an external collection and monitoring system. The ventriculostomy has two primary functions: to drain excess cerebrospinal fluid (CSF) and to provide continuous, accurate measurement of the intracranial pressure (ICP). This dual capability makes it an indispensable tool in neurocritical care.
Why is a Ventriculostomy Necessary
The brain and spinal cord are cushioned by cerebrospinal fluid (CSF), which circulates within the ventricular system. Since the skull is closed, any increase in the volume of brain tissue, blood, or CSF causes intracranial pressure (ICP) to rise dangerously. Sustained elevated ICP compresses delicate brain tissue and compromises cerebral perfusion pressure (CPP), the force driving blood to the brain.
A ventriculostomy is indicated for intracranial hypertension, typically defined as an ICP consistently above 20 to 25 millimeters of mercury (mmHg). This high-pressure state often results from severe traumatic brain injury (TBI) or acute hydrocephalus (abnormal buildup of CSF). It is also required after an intracerebral or subarachnoid hemorrhage, where blood obstructs normal CSF flow and absorption.
Direct CSF drainage provides an immediate and effective means of reducing pressure within the skull. This therapeutic drainage is precisely managed to maintain a target ICP, preventing secondary brain injury. The ability to both measure and treat intracranial hypertension concurrently makes the ventriculostomy the most definitive method for managing elevated ICP.
The Procedure: Placement and External Mechanics
The procedure involves a controlled surgical process to ensure accurate catheter placement. A small incision is made on the scalp, and a burr hole is drilled through the skull, typically at Kocher’s point. This landmark provides the safest route into the frontal horn of the lateral ventricle. The catheter is then carefully advanced toward the ventricle, often guided by anatomical measurements or neuronavigation technology.
Once the catheter tip is confirmed to be within the ventricle, it connects to the external ventricular drain (EVD) system. This system uses gravity drainage; the height of the collection chamber relative to the patient’s head determines the pressure at which CSF flows out. The system must be carefully “zeroed” by leveling the pressure transducer to the Foramen of Monro, the central point of the ventricular system.
For a patient lying flat, this zero reference point is often the tragus of the ear. Leveling ensures accurate ICP readings, as minor height changes alter the measured pressure due to hydrostatic effects. A pressure transducer converts the fluid pressure into an electrical signal, allowing continuous display of the ICP waveform on a bedside monitor. This constant monitoring allows for immediate adjustments to the drainage rate, managed by a three-way stopcock system.
Potential Risks and Management
The insertion of a foreign device carries specific risks, primarily infection, known as ventriculostomy-related infection (VRI) or ventriculitis. The risk increases the longer the drain remains in place. Pathogens, often common skin bacteria, can colonize the catheter, leading to a serious infection of the CSF.
Another potential complication is hemorrhage, or bleeding, which can occur during insertion or along the catheter’s path. Although often minor, significant bleeding may necessitate immediate drain replacement or cause new neurological deficits. Mechanical failure is also possible, such as the catheter becoming blocked by blood clots or debris, preventing both drainage and accurate pressure monitoring.
To mitigate these risks, management protocols emphasize meticulous sterile technique during insertion and manipulation. The EVD system must remain a closed, sterile circuit to minimize bacterial entry. Frequent neurological assessments and monitoring of the CSF for signs of infection are performed. Some facilities use catheters impregnated with antibiotics to reduce colonization.
What Happens After the Ventriculostomy
A ventriculostomy is a temporary intervention, used until the underlying cause of elevated ICP is resolved or the brain restores its ability to manage CSF. The process of removing the drain, known as weaning, begins when the patient’s condition stabilizes and ICP remains acceptable without drainage. Weaning protocols involve a trial period where the EVD is gradually raised or clamped entirely.
During a clamp trial, the drainage stopcock is turned off, forcing the patient’s body to absorb the CSF. The patient is closely observed for clinical decline, such as worsening headache or decreased consciousness, and for sustained increases in ICP. If the patient remains stable and the pressure stays low for a set period, the catheter is safely removed.
If the patient fails the weaning trial (ICP rises or symptoms develop when clamped), they have shunt-dependent hydrocephalus. In these cases, the ventriculostomy is replaced by a permanent CSF diversion system, typically a ventriculoperitoneal (VP) shunt. This permanent shunt routes excess CSF from the ventricles to the abdomen, where it is safely absorbed.