Intracranial pressure (ICP) monitors are devices that measure ICP and are generally placed in any patient in whom there is concern for elevated ICP.
Intracranial pressure (ICP) monitor
External Drainage Catheters
Ventrix Ventricular Tunneling Pressure Monitor
Camino Micro Ventricular Bolt Pressure Monitor
Camino Intracranial Pressure Monitor with Licox Bolt
Camino OLM Intracranial Pressure Monitor
Camino Post Craniotomy Subdural Pressure Monitor
Microsensor (subdural, intraparenchymal, and intraventricular)
ICT/B subdural intracranial pressure monitor
There are two basic types of ICP monitors. One type provides ICP data only (commonly referred to as a “bolt”), whereas the other allows concurrent drainage of cerebrospinal fluid (CSF) while ICP is being measured (ventriculostomy or intraventricular catheter).
Monitors that detect changes in pressure on the basis of flow through a fluid-filled system are most accurate when the system is closed to drainage. The combination of a ventriculostomy with a closed drainage system is also known as an external ventricular drain (EVD). Bolts commonly use fiberoptic technology that allows continuous ICP monitoring without CSF drainage. The fiberoptic type of catheter can be placed in the subdural space or in the brain parenchyma, whereas the EVD is not accurate unless it is located in the intraventricular space.
Integra Neuroscience products
The Integra Neuroscience external drainage catheter is a CSF diversion device that also measures ICP. The catheter tubing is translucent with depth markings and contains a radio-opaque barium sulfite strip. ICP readings are based on a fluid-filled transduction system that transmits changes in ICP through a saline-filled tube to a diaphragm on a strain gauge transducer. [1, 2, 3] This monitor must be leveled with the foramen of Monro (approximately the level of the external auditory canal) after insertion and should be zero-balanced daily. The level of the drain can be adjusted to allow more or less CSF drainage.
Similarly, the Integra Neuroscience Ventrix catheter allows CSF diversion and ICP monitoring. This catheter contains a fiberoptic pressure monitor that must be zero-balanced in air prior to insertion. The Ventrix catheter is tunneled under the scalp and inserted into the ventricle to allow CSF drainage as well as ICP monitoring. 
The Camino microventricular bolt pressure monitor also drains CSF and monitors ICP without the need to tunnel underneath the scalp. The distal tip of the catheter contains a small fiberoptic transducer, eliminating the external transducer and the need for a fluid-filled system of pressure conduction. The catheter must be zero-balanced before insertion. 
Integra also has multiple devices designed to measure ICP without draining CSF. These monitors use a fiberoptic transducer that senses changes in the amount of light reflected from a pressure-sensitive diaphragm located at the monitor tip. [6, 7]
The Camino ICP monitor designed to be used with the Licox bolt system is a fiberoptic cable attached to a microtransducer that transmits pressure waves without a fluid filled column, allowing for continuous measurements. The transducer must be zero-balanced before insertion into brain parenchyma. 
The Camino OLM ICP monitor measures ICP in the intraparenchymal tissue or subarachnoid space. It contains a transducer at the distal tip, thus measuring pressure without a fluid-filled system. The catheter is secured to the skull through an adjustable bolt, allowing placement at variable depths (up to 5 cm). The transducer must be zero-balanced before insertion. 
The postcraniotomy subdural pressure monitor utilizes the craniotomy bur holes and flap as a point of entry. The monitor is zero-balanced and then tunneled under the scalp toward the craniotomy bur hole of choice and positioned in the subdural space. The bone flap is secured in routine fashion. This monitor contains a microtransducer at the tip, which is similar to the microventricular catheter and the OLM ICP monitor. 
The Codman Microsensor catheter can be used as an intraparenchymal or intraventricular monitor, depending on the depth of the catheter. Different drill bits are used to allow for variable depths of measurement. If used as an intraventricular monitor, the catheter also allows CSF drainage. This system uses a fiberoptic transducer that must be zero-balanced before insertion.  The Codman ICP monitor uses a microminiature strain gauge located at the tip of the monitor that transmits changes in pressure over a diaphragm. Changes in electrical resistance are reflected on an external monitor. [6, 12]
The ICT/B pressure sensor is intended to monitor ICP subdurally. It contains a balloon-covered pressure sensor that is activated when filled with air. This monitor is self–zero-balanced in vivo and is reusable. 
Spiegelberg ICP monitors measure ICP through an air-pouch system attached to a pressure transducer connected to an electronic device. The probes differ, depending on where they rest. The epidural probes air pouch rests on the dura. The risk of infection is minimal for these probes.
Other products include intraparenchymal probes, for which the air pouch is placed in the parenchyma through a bur hole or tunneled away with a trocar. Ventricular catheters are silverline ventricular probes with a cranial bolt. The air pouch is mounted at the tip of the ventricular catheter, and there are two lumina, one for drainage of CSF and the other filled with air for measurement of ICP. 
Intracranial pressure (ICP) monitors are devices that measure ICP and are generally placed in any patient in whom there is concern for elevated ICP. These devices were first used in the 1970s in patients with Reye syndrome and are now commonly used in trauma patients with severe head injuries, subarachnoid hemorrhage, large strokes, or structural lesions. [6, 15, 16]
ICP monitoring is considered important for the management of acute brain injury because the brain is enclosed by the skull, a fixed container; thus, according to the Monro-Kellie doctrine, any addition to this space, such as a hematoma, raises ICP. Although its benefit is still not clearly established, ICP monitoring can help in guiding treatment of brain-injured patients.
ICP monitoring facilitates aggressive therapy to maintain adequate blood perfusion in traumatic brain injury (TBI), minimizing secondary injury. The secondary injury in TBI is a cascade of inflammatory response that can increase edema and affect blood perfusion, with the consequence that the brain injury may be extended. ICP monitoring allows assessment of the efficay of treatment in brain injury.
Normal ICP is less than 20-25 mm Hg, and sustained pressures in the range of 20-30 mm Hg are associated with increased mortality.  Most neurocritical care specialists and trauma surgeons base their medical management on maintaining cerebral perfusion pressure (CPP), which is calculated by subtracting the ICP from the mean arterial pressure (MAP). [7, 1] Several studies have shown that close ICP monitoring leads to either medical or surgical interventions resulting in decreased mortality. [18, 19]
About 50% of patients with severe TBI and abnormal computed tomography (CT) scans have an elevated ICP  ; accordingly, Brain Trauma Foundation guidelines recommend ICP monitor placement in any patient with a severe head injury who has an abnormal CT scan.  These patients are defined as having a Glasgow Coma Scale (GCS) score of 3-8 after adequate cardiopulmonary resuscitation. Abnormal CT scan findings include hematomas, contusions, and generalized edema.
Additionally, there is level 3 evidence for ICP monitor insertion in patients with a normal CT scan if the patient has at least two of the following criteria  :
Age older than 40 years
Systolic blood pressure below 90 mm Hg
See the image below.
ICP monitoring and CSF drainage are also commonly used in patients with acute hydrocephalus, which may be caused by subarachnoid hemorrhage, intraventricular hemorrhage, or mass lesions. A ventriculostomy insertion allows ICP monitoring, as well as CSF drainage, thereby alleviating ICP. Ventriculostomies may also be useful in patients with meningitis who have hydrocephalus, both for CSF drainage and for antibiotic delivery. [6, 15]
Clinical Trial Evidence
No level 1 evidence supports the use of intracranial pressure (ICP) monitoring; however, case series and prospective nonrandomized studies suggest that such monitoring improves patient outcomes, especially in the setting of trauma. Dissenting studies dispute these findings, and the superiority of ICP monitor–based treatment of traumatic brain injury (TBI) is not established. [18, 19, 21, 22, 23]
In a large case series involving patients with ICP monitors who suffered closed head injuries secondary to blunt trauma, 81% received treatment interventions based on elevated ICP.  In a retrospective chart review of Canadian trauma patients who suffered closed head injuries, a statistically significant decrease in mortality was reported when an ICP monitor was used.  Talving et al examined ICP monitoring practice at a single institution and found that compliance with Brain Trauma Foundation (BTF) guidelines was 47%. In patients who underwent ICP monitoring, they had significantly lower in-hospital mortality and mortality due to brain herniation. 
Although these nonrandomized series are prone to bias, the contention that ICP monitoring can guide management and may improve outcomes among patients who suffer severe closed head injuries has been noted.
In contrast to the positive studies, Shafi et al analyzed results from the National Trauma Data Bank (1994-2001) and found that only 43% of patients who met the BTF criteria underwent ICP monitoring. Patients who received monitoring had a 45% reduction in survival.  Chesnut et al published a randomized study that divided patients treated in trauma centers in Bolivia and Ecuador into two groups, one assessed with ICP monitoring and the other with imaging and clinical examinations. No difference was reported in the primary outcome (functional and cognitive outcome or survival at 6 months). 
Several studies have compared the various methods of ICP monitoring and their accuracy. Schicker et al  compared the Camino fiberoptic monitor ICP readings with external ventriculostomy in 10 patients for 118 hours. They found that the Camino monitor reported a higher ICP than the external ventricular drain (EVD) 66% the time, with an average difference of 9.2 mm Hg, a larger difference than that reported by Ostrup et al, which was 2-5 mm Hg. 
In a study comparing fiberoptic intraparenchymal monitors with external ventriculostomies in 62 children, Exo et al  found a high correlation between the two devices but noted that some readings were delayed with the EVD because it must be closed for accurate determination of ICP. They recommended placing both an intraparenchymal ICP monitor and an EVD to allow continuous ICP measurements and drainage of CSF.
Weinstabl et al  compared the Gaeltec epidural ICP monitor with the Camino subdural ICP monitor in vitro using a tightly closed fluid-filled box to represent the skull and confirmed their findings clinically in 10 patients. In the clinical setting, a minimal difference in ICP readings was found between the two types of monitors; however, the study did find that the Gaeltec epidural monitor had higher readings when the ICP measured more than 20 mm Hg. The Camino subdural monitor malfunctioned more often frequently and was found to have a greater zero-drift.
Martinez-Manas et al  prospectively analyzed 180 Camino fiberoptic pressure monitors (intraparenchymal, subdural, and intraventricular) to determine their accuracy and their associated complication rates. The most common complications were infection (13.2%) and hemorrhage (2.1% in patients without a coagulopathy and 15.3% in patients with a coagulopathy). Infections occurred more often in monitors that were kept longer than 10 days. Of the 56 catheters that were analyzed for zero-drift, 60.7% of the probes were within the manufacturer’s specifications.
Poca et al  also prospectively analyzed the Camino intraparenchymal monitor in 163 head-injured patients and found that none of their patients developed an infection. Of these devices, 12.8% had a technical malfunction such as lead fracture, 63.5% overreported the ICP, 11.1% showed no drift, and 25.4% underreported the ICP on the basis of postremoval analysis. They did not find a correlation between the length of time the monitor was in place and the amount of zero-drift.
Piper et al  assessed the accuracy of the Camino ICP monitor and also found a 10% malfunction rate. Zero-drift was found in 50% of patients, but only 6% had a drift exceeding 3 mm Hg. Like Poca et al, they did not find a correlation between duration of monitoring and zero-drift.
Fernandes et al  analyzed the Codman Microsensor ICP monitor by comparing it to the Camino ICP monitor in eight patients with head trauma or intracranial hemorrhage. One monitor of each type mechanically failed. The Codman Microsensor monitor drifted in comparison to the Camino ICP monitor in two cases, once in the positive direction and once in the negative. Overall, the Codman microsensor reading were higher by 5 mm Hg in 24% of the patients and by 10 mm Hg in 9% of patients; however, owing to the small sample size, further device studies are needed to accurately compare the two monitors.
Al-Tamini et al  assessed the zero-drift of Codman ICP monitors in 88 ICU patients. The median zero-drift was 2 mm Hg, with a drift of 5 mm Hg in 20% and 10 mm Hg in 2%.
Intracranial pressure (ICP) monitors can be inserted in the operating room or at the bedside, either in the intensive care unit or in the emergency department. The monitor is traditionally placed in the right frontal region, but the location can vary in accordance with an individual patient’s pathology. (See Intracranial Pressure Monitoring.)
The area around the incision is clipped and cleaned. With sterile technique, the scalp is incised, and a small hole is drilled through the skull. The ICP monitor is inserted through this hole and passed to various depths depending on the type of monitor being used. The Camino postcraniotomy subdural monitor is usually inserted intraoperatively, with one of the craniotomy bur holes serving as the insertion point.
These monitors can be left in place for several days. Integra recommends replacing the Camino fiberoptic monitors after about 5 days to ensure accurate ICP readings.
ICP monitors can easily be removed at the bedside, and the entry point is closed with sutures to prevent cerebrospinal fluid (CSF) leaks.
Accurate placement of the intracranial pressure (ICP) monitors is usually assessed by means of computed tomography (CT) of the head. Cerebrospinal fluid (CSF) can be routinely checked for meningitis in patients with external ventriculostomies, but not with fiberoptic monitors.
The major complications associated with all intracranial pressure (ICP) monitors include infection and hemorrhage. Despite the use of sterile technique during insertion, there is a risk of meningitis and wound infection, which ranges from 1% to 27% and is higher with external ventriculostomy insertion. [18, 1, 26, 27] Fiberoptic monitors have a lower risk of infection, ranging from 0% to 1.7%.  Most infections are caused by gram-positive organisms such as Staphylococcus species.
All surgical procedures are associated with a risk of hemorrhage. Patients who undergo ICP monitor insertion may develop an intraparenchymal hematoma surrounding the catheter trajectory or subdural hematomas. The rate of hemorrhage varies by type. Subdural monitors are associated with approximately a 5% rate of hemorrhage, compared with a 4% risk for intraparenchymal catheters and a 1.1% risk for ventricular catheters. [25, 30, 16, 28, 2] The incidence of hemorrhage also increases in patients with coagulopathy or hypothermia. [6, 15, 26, 27]
Technical malfunction can lead to inaccurate readings and occurs with both fiberoptic and strain-gauge monitors. Fiberoptic transducers can be damaged by excessive kinking or bending, which may affect their accuracy and function. Additionally, these monitors are subject to zero-drift, which can be significant [29, 24, 28, 2] and may result in inappropriate ICP management.
External ventricular drains (EVDs) can become occluded with brain tissue or blood clot and also must be zero-balanced on a regular basis to ensure accuracy. These monitors have been found to drift by ±2 mm Hg every 8 hours.  EVDs are typically re-zeroed any time the drain height is adjusted, the patient is moved, or any time the reading does not seem to correlate with the patient’s clinical status.