The procedure that allows for intracranial pressure (ICP) monitoring in hemorrhagic stroke is placement of an external ventricular drain, commonly called an EVD or ventriculostomy. It is the most common neurosurgical procedure performed for this purpose and can be done at the bedside. Beyond simply measuring pressure, an EVD also drains cerebrospinal fluid (CSF) to actively reduce dangerous pressure buildup inside the skull.
How an EVD Works
An EVD is a thin, flexible catheter inserted through a small hole in the skull into one of the brain’s fluid-filled chambers (the lateral ventricles). The catheter connects to an external collection system that includes a pressure transducer. This transducer converts the physical force of fluid pressing against it into a numerical ICP reading displayed on a bedside monitor.
The system serves two functions: monitoring and treatment. By opening a stopcock on the drainage system, CSF can flow out of the ventricle and into a collection bag, directly lowering the volume of fluid inside the skull and reducing pressure. To get an accurate ICP reading, the drain must be temporarily closed so the fluid pressure stabilizes against the transducer. In other words, the EVD can either monitor ICP or drain fluid at any given moment, but not both simultaneously.
Accurate readings depend on proper positioning. The pressure transducer must be level with a landmark called the foramen of Monro, which corresponds roughly to the ear canal when a patient is lying on their back. Nurses use a carpenter’s level or laser device to confirm alignment, since visual estimates alone are often inaccurate. Every time the patient changes position, the system needs to be re-leveled to prevent false readings or unsafe drainage.
Why ICP Monitoring Matters in Hemorrhagic Stroke
When bleeding occurs inside the brain, the blood takes up space in a closed compartment (the skull), pushing pressure upward. If blood spills into the ventricles, it can also block the normal flow of CSF, causing a dangerous buildup of fluid called acute hydrocephalus. Both situations raise intracranial pressure, which can compress brain tissue and cut off blood supply to critical areas.
The first ICP reading taken when the EVD is placed, called the opening pressure, is one of the most important pieces of clinical data. It tells the medical team how severe the pressure problem is and guides treatment intensity. From that point on, continuous monitoring allows clinicians to track whether pressure is rising, falling, or responding to drainage.
ICP data also feeds into a broader calculation: cerebral perfusion pressure (CPP), which reflects how much blood is actually reaching the brain. CPP is calculated by subtracting ICP from mean arterial blood pressure. American Heart Association/American Stroke Association guidelines suggest maintaining a CPP of 50 to 70 mmHg in hemorrhagic stroke patients, depending on the individual’s condition.
Who Needs an EVD
Not every hemorrhagic stroke patient requires an EVD. Current AHA/ASA guidelines recommend considering ICP monitoring and treatment for patients who score 8 or below on the Glasgow Coma Scale (a measure of consciousness), those showing signs that brain tissue is being pushed downward through the skull’s internal openings (transtentorial herniation), or those with significant bleeding into the ventricles or hydrocephalus. These criteria identify patients at highest risk for life-threatening pressure elevation.
How EVDs Compare to Other Monitors
EVDs are not the only way to measure intracranial pressure. Parenchymal monitors are small sensors placed directly into brain tissue rather than into a ventricle. These devices use fiberoptic, strain-gauge, or air-bladder technology and provide reliable ICP readings considered second in accuracy only to ventricular monitoring. However, parenchymal monitors have one major limitation: they cannot drain CSF. They watch the problem but cannot treat it.
This distinction is what makes the EVD uniquely valuable in hemorrhagic stroke. It combines a diagnostic tool (pressure measurement) with a therapeutic one (fluid drainage) in a single device. Some newer approaches pair a parenchymal sensor with a ventricular catheter, dedicating the sensor to continuous ICP monitoring while freeing the catheter for uninterrupted CSF drainage. This avoids the need to pause drainage every time an ICP reading is needed.
Infection and Complication Risk
Because an EVD creates a direct pathway from the brain’s interior to the outside environment, infection is the primary concern. Reported infection rates typically fall between 10 and 17 percent, though rates as low as zero and as high as 45 percent have been documented depending on the facility and patient population. Two factors significantly increase infection risk: keeping the drain in place for five or more days and any leakage of CSF around the catheter site.
To manage this risk, medical teams monitor CSF samples for signs of infection throughout the time the drain is in place. Strict sterile technique during insertion and maintenance, along with minimizing how often the system is accessed, helps reduce contamination.
Weaning and Removal
An EVD is not meant to stay in permanently. Once the underlying cause of elevated pressure is resolving, the team begins a structured weaning process. Weaning typically starts when daily CSF output drops below 250 mL over 24 hours, the fluid is no longer bloody, ICP readings are within normal limits, and the patient is neurologically stable.
The process involves gradually raising the drain height by 5 mmHg every 24 hours. This makes it progressively harder for CSF to flow out, testing whether the brain can manage fluid circulation on its own. Once the drain reaches 20 mmHg, it is clamped shut entirely. If a CT scan taken 24 hours after clamping shows stable ventricle size, the catheter is removed.
Newer Minimally Invasive Approaches
Minimally invasive surgical techniques for removing blood clots from the brain are evolving to incorporate real-time ICP monitoring. Systems like the NICO BrainPath and Penumbra Apollo use controlled suction to evacuate blood while preserving surrounding tissue. Some of these approaches now integrate pressure sensors that allow the surgical team to monitor ICP during the procedure itself, adjusting suction intensity based on real-time pressure feedback. Robot-assisted versions of these procedures can pair multisensor probes with clot removal, helping restore normal pressure in a more controlled, stepwise fashion. These remain specialized techniques available primarily at advanced neurosurgical centers, but they represent a shift toward combining clot removal and pressure management into a single operation.