Intracranial Pressure (ICP) is the pressure exerted by fluids and tissues within the skull. A medical transducer converts physical pressure into a readable electrical signal, and an ICP transducer system is a medical instrument used to continuously measure this pressure. The system works by placing a sensitive monitor inside the head, which detects pressure and sends measurements to an external recording device.
This system provides real-time data, allowing for immediate intervention if pressure rises to dangerous levels. This technology is used in neurocritical care to manage brain health after a severe injury or illness. The data informs treatment decisions to protect the brain from the damaging effects of high pressure.
Purpose of ICP Monitoring
The skull is a fixed structure that encloses the brain, cerebrospinal fluid (CSF), and blood. Because the skull cannot expand, any increase in the volume of its contents leads to a rise in pressure. This elevated ICP can compress brain tissue and restrict blood flow, depriving brain cells of oxygen and leading to injury.
ICP monitoring is used for patients with conditions that cause brain swelling or an accumulation of fluid. Common situations include:
- Traumatic brain injury (TBI), where the brain can swell significantly after an impact, causing a dangerous spike in pressure.
- Hydrocephalus, a condition characterized by an excess of CSF that requires monitoring to guide drainage and manage pressure.
- Large strokes (cerebral hemorrhage), which can cause bleeding and swelling within the brain.
- Brain tumors that increase pressure by adding mass within the skull.
- Severe central nervous system infections like meningitis or encephalitis, where inflammation leads to brain swelling.
Types of ICP Monitoring Systems
Several types of devices are used to measure intracranial pressure. The most common system is the External Ventricular Drain (EVD), considered the gold standard for ICP measurement. An EVD consists of a thin, flexible catheter inserted through brain tissue into one of the brain’s fluid-filled spaces, the lateral ventricles.
The EVD serves a dual purpose. It connects to a system that transmits pressure changes to an external transducer, providing continuous ICP readings. Simultaneously, the catheter allows for the controlled drainage of excess cerebrospinal fluid (CSF) from the ventricles, which helps to lower high pressure. This ability to both monitor and treat makes the EVD a comprehensive tool.
Another category includes intraparenchymal devices, which are placed directly into the brain tissue (parenchyma). These monitors use fiber optic or strain-gauge technology. Fiber optic systems send light to a pressure-sensitive diaphragm at the sensor’s tip, and changes in reflected light correspond to pressure changes. Strain-gauge monitors use a diaphragm that alters electrical resistance when bent by pressure. While highly accurate, these devices only measure pressure and cannot drain CSF.
The Monitoring Procedure
Placing an ICP monitor is a surgical procedure performed in an operating room or at a patient’s bedside in the intensive care unit (ICU). The process begins with preparing a small area of the scalp with an antiseptic solution. A surgeon then makes a small incision to expose the skull.
Using a specialized drill, a small opening called a burr hole is created in the skull. Through this hole, the monitoring device—either a catheter for an EVD or a sensor for an intraparenchymal monitor—is inserted to its target depth. An EVD catheter is advanced into a ventricle, while an intraparenchymal sensor is placed within the brain tissue.
Once the device is positioned, it is secured in place. The external portion of the catheter or wire is connected to the transducer and bedside monitoring equipment. This monitor displays ICP readings as both a numerical value and a pressure waveform, providing continuous data. The patient remains under close observation in the ICU during the monitoring period.
Interpreting the Data and Associated Risks
Normal ICP in a resting adult is below 20 to 25 millimeters of mercury (mmHg). A sustained elevation above this level requires immediate medical intervention to prevent brain damage. Clinicians also analyze the shape of the ICP waveform, as its morphology can provide insights into the brain’s compliance, or its ability to tolerate volume changes.
Treatments for high ICP include adjusting the patient’s position, changing ventilator settings, and administering medications to reduce swelling. If an EVD is in place, CSF can also be drained. The goal is to maintain adequate cerebral perfusion pressure, which is the pressure gradient that drives blood flow to the brain.
ICP monitoring is an invasive procedure and carries certain risks. The most significant is infection, as the device creates a direct pathway into the brain, potentially leading to meningitis or ventriculitis. There is also a risk of bleeding at the insertion site. Additionally, the device can malfunction, with catheters becoming blocked or sensors providing inaccurate readings that require repositioning or replacement.