Intracranial pressure (ICP) refers to the pressure inside the skull, which encases the brain, cerebrospinal fluid (CSF), and blood. Maintaining this pressure within a normal range is important for proper brain function and overall health. In healthy adults, ICP typically ranges from 5 to 15 millimeters of mercury (mmHg) when lying flat.
This pressure needs to be regulated because the skull is a rigid compartment. Any increase in the volume of its components, like brain tissue, blood, or CSF, will cause the overall pressure to rise. If ICP becomes too high, it can compress brain tissue and blood vessels, potentially leading to serious consequences. An intracranial pressure monitor is a specialized device used by healthcare professionals to continuously measure this pressure.
Conditions Requiring Monitoring
Various medical conditions can lead to dangerous fluctuations in ICP, making monitoring a necessary part of patient care. Traumatic brain injury (TBI) is a common cause, where the brain can swell or bleed following an impact, directly increasing the volume inside the skull. Strokes, whether ischemic (due to a blood clot) or hemorrhagic (due to bleeding), can also elevate ICP. Ischemic strokes cause brain tissue swelling, while hemorrhagic strokes add volume from accumulated blood.
Hydrocephalus, an excessive buildup of cerebrospinal fluid in the brain’s ventricles, increases ICP. Brain tumors, as they grow, occupy space within the skull, leading to a rise in pressure. Severe infections of the brain and its surrounding membranes, such as meningitis or encephalitis, can cause inflammation and swelling, thereby increasing ICP. Liver failure can also contribute to elevated ICP through the accumulation of toxins in the bloodstream, which can lead to brain swelling.
Types of ICP Monitors and Their Function
Several types of ICP monitors are available, each placed in a specific location to measure pressure within the cranial vault. The external ventricular drain (EVD) measures ICP and can also drain excess cerebrospinal fluid, which helps to lower pressure. An EVD involves inserting a thin catheter directly into one of the brain’s fluid-filled ventricles.
Intraparenchymal monitors are placed directly into brain tissue. These fiber optic or strain gauge sensors detect changes in pressure, providing continuous readings.
Subdural monitors are positioned in the subdural space, between the dura mater (the outermost membrane covering the brain) and the arachnoid mater (the middle membrane). Epidural monitors are placed in the epidural space, between the skull and the dura mater. Both subdural and epidural monitors provide an indirect measurement of ICP.
What to Expect During Monitoring
The placement of an ICP monitor is typically a sterile procedure, performed in an operating room or intensive care unit (ICU). Patients usually receive a local anesthetic and sedation for comfort during insertion. A small incision is made in the scalp, and a burr hole is drilled into the skull for monitor insertion.
Once the monitor is in place, the incision is closed, and a dressing is applied. Wires extend from the head, connecting to a bedside monitor that displays ICP readings. Nursing staff maintain the monitor, ensuring its proper function, and monitoring the patient’s neurological status. The monitor generally remains in place for as long as continuous ICP data is needed, ranging from a few days to a week or more, depending on the patient’s condition.
The monitoring itself is non-invasive once secured, meaning no further surgical interventions are required for daily pressure readings. When the monitor is no longer needed, it is carefully removed. The incision site is then dressed, and it typically heals without significant issues.
Interpreting Results and Potential Complications
Understanding ICP readings is important for guiding treatment decisions. A normal ICP in adults falls between 7 and 15 mmHg. Readings consistently above 20 mmHg are elevated and indicate a need for intervention. Dangerously low readings can also occur, suggesting issues like over-drainage of CSF or a leak.
Doctors use this pressure data to adjust treatments. If ICP is high, medications can be administered to reduce brain swelling or sedate the patient. If an external ventricular drain is in place, doctors can drain cerebrospinal fluid to lower the pressure directly. In some cases, surgical interventions address the underlying cause of elevated ICP.
Despite the benefits of ICP monitoring, there are potential risks and complications. Infection is a concern, including meningitis (inflammation of brain and spinal cord membranes) or ventriculitis (infection within the brain’s ventricles), as the monitor provides a pathway for bacteria. Bleeding can occur during device insertion or while it is in place. Device malfunction can lead to inaccurate readings or replacement. There is a small risk of brain tissue damage during monitor insertion or removal.