How is icp monitored

However, depending on known or suspected pressure gradients across intracranial compartments, the placement can be modified. Regarding epidural ICP monitoring, currently it does not provide the necessary accuracy for routine use. Another study showed a markedly differing mean ICP, but comparable parameters of pulsatile ICP mean wave amplitude and wave rise time [ 71 ].

In a newer study comparing lumbar cerebrospinal fluid pressure to epidural and subdural ICP [ 73 ], an excellent correlation was found between the lumbar and subdural pressure measurements. However, higher pressure values were consistently found for ICP measured in the epidural space with increasing distance between the lumbar and epidural values at higher pressure intervals.

The authors concluded that the higher ICP in the epidural space was due to physiologically different pressures in the two compartments and not due to technical aspects. For current use in critical care, subdural sensors may be considered for use if there is no suspicion of focal ICP elevations with potential for causing intercompartmental pressure gradients. However, this will seldom be the case, and intraparenchymal or intraventricular monitors should be considered the standard choice.

Complications are, as with EVDs, mainly the risk of hemorrhage and infection. Similar study by Piper et al. The authors state that no infections were diagnosed in the study population; however, one patient had a fever and a positive bacterial culture from the catheter tip, but no bacterial growth in the CSF.

A large study by Koskinen and Olivecrona [ 78 ] state, that after insertion of almost Codman MicroSensors, only 3 incidents of surgically related hemorrhages were found, none of which required surgical intervention. No infections were linked to the placement of the MicroSensor. No CNS infections were registered.

The relatively new Pressio sensor has yet to be tested thoroughly in vivo. Only clinical study currently available, is that by Lescot et al. Complications were not recorded.

The Spiegelberg sensor has been tested by Lang et al. None of the patients showed clinical signs of meningitis. In three patients, a leak related to the sensor resulted in incorrect measurements.

Kiening et al. Despite unsatisfactory results in the current clinical care setting, the same authors [ 83 ] later found a correlation between increasing age and decreasing compliance and speculated that this correlation might contribute to the poorer outcome seen in elderly patients after TBI.

It is worth mentioning, that the Neurovent-P sensor, the Spiegelberg sensor and the Codman MicroSensor are compatible with magnetic resonance imaging MRI without any danger to the patient. The Camino monitor and Pressio sensor contain ferromagnetic components, and therefore patients with these devices cannot undergo MRI [ 84 — 86 ].

Generally, several of the above studies concluded that when it comes to measuring ICP, microtransducers are just as accurate as the EVDs [ 69 , 81 ]. However, microtransducers share a common disadvantage, in that no recalibration is possible after placement; though the Spiegelberg catheter is an exception from this rule, as it recalibrates itself every hour. The amount of CSF drained depends on the pressure gradient inside the CSF cavity and the resistance of the CSF drainage, the resistance being defined by the pressure gradient of the CSF has to overcome to reach the level of the drip chamber.

This means that the position of the drip chamber relative to the CSF space is the crucial factor for the amount of drained CSF. The lack of continuous calibration can cause the sensor to report imprecise ICP values. Therefore, the cumulative pressure difference can have important implications for the treatment and prognosis of the patient.

Data regarding differences between microtransducer ICP monitoring devices is summarized in Table 2. The idea of a noninvasive method of measuring ICP is captivating, as complications seen in relation to the invasive methods of ICP measuring, that is, hemorrhage and infection, are avoidable. Different techniques have been proposed; however, in this paper we will focus on the ones most widely familiar. The TCD technique applies ultrasound to initially measure the blood flow velocity in the middle cerebral artery.

The difference between systolic and diastolic flow velocity, divided by the mean flow velocity, is called the pulsatility index PI : PI is found to correlate with invasively measured ICP [ 90 — 92 ], and correlation coefficients between 0, and 0, have been found.

Bellner et al. A deviation of this small magnitude is clinically acceptable. However, this small magnitude of deviation only applies to ICP values lower than approx. The apparently high correlation includes great individual variations in the data. A variation of this magnitude is clearly unacceptable for clinical use. Behrens et al. Brandi et al.

In their study, 45 sedated patients with severe traumatic brain injury, each monitored with a Raumedic probe, were examined daily using TCD. The best correlation was found by using the calculations proposed by Bellner et al. Apart from being imprecise, the technique requires training and repetitive exercise [ 95 ], and there is also intra- and inter-observer variations as noted earlier [ 95 — 98 ]. The technique takes advantage of the communication of the CSF and the perilymph via the perilymphatic duct.

Stimulation of the stapedial reflex causes a movement of the tympanic membrane, which is shown to correlate to ICP [ , ]. Stapes rests on the oval window, which is covered by a membrane. This membrane is flexible, meaning that the pressure of the fluid in the cochlea affects how the membrane and stapes are positioned and how they move. A quantitative measurement of this movement is the fundament of this technique.

However, the technique is not without flaws; Shimbles et al. It was noted, that the low rate of success was mainly due to the perilymphatic duct being less passable with age, especially after the age of Furthermore, a subgroup of cases in the patient population were invasively ICP monitored at the time of the experiment.

However, intersubject variability was so great that the predictive limits of the regression analysis was an order of magnitude greater than normal ICP range, thus precluding the method for clinical use [ ].

The optic nerve is part of the central nervous system, and therefore surrounded by the dural sheath. In cases of increased ICP, the sheath expands. Changes in the diameter of the nerve sheath can be visualized using transocular ultrasound. Several studies [ — ] have investigated the correlation between the nerve sheath diameter and invasively measured ICP. A correlation coefficient of between 0,59—0,73 has been found. The technique is cheap and efficient; the examination takes around 5 minutes per patient [ ].

However, as with all ultrasonography, it requires training and has intra- and inter-observer variance, though these variations are minor. Furthermore, it is important to mention that several conditions can affect optic nerve diameter, for example, tumors, inflammation, Graves disease, and sarcoidosis [ , ]. Patients with glaucoma and cataract have been excluded from the above study population, and it is therefore uncertain, whether the technique can be applied on patients with these common conditions.

At present, the technique does not seem to be accurate enough to be used as a replacement for invasive ICP measuring methods. Another study by Rajajee et al.

This means that this technique can potentially be used as a screening method for detecting raised ICP in settings, where invasive ICP monitoring capabilities are not available, that is, hospitals without access to a neurosurgeon. In , Alperin et al. By using motion-sensitive MRI, pulsatile arterial, venous, and CSF flow in and out of the cranial vault during the cardiac cycle was measured. An elastance index was derived from the ratio of pressure to volume change and found to correlate well with invasively measured ICP ;.

However, as Marshall and colleagues pointed out, care is required in the selection of representative image slides as well as choosing the representative blood vessels [ ]. Furthermore, the technique is very sensitive to differences in heart rate measured in the circulation contra the CSF flow rate as well as CSF measurements.

Even when the above was addressed, some subjects displayed significant variation between repeated measurements, requiring for the data gathered from individual cases to be interpreted with caution [ ]. However, if we can accept these shortcomings, the technique could have a role as a screening tool for identification of patients in need of invasive ICP monitoring after moderate head trauma.

It could also play a role in diagnosis and evaluation of several chronic disorders potentially associated with increased ICP values, i. A way of interpreting ICP values from cranial CT scans has also been investigated; the majority of studies were conducted in the late s and early s and failed to show consistent correlation between ICP and CT scan characteristics [ ].

In , Eide reported no significant correlation between actual size or change in size of cerebral ventricles by cranial CT scans and invasively monitored ICP in consecutive patients [ ]. A linear, but ultimately nonpredictive relationship between baseline ICP and initial head CT scan characteristics was found by Miller and colleagues [ ]. Similar results were observed by Hiler et al. Nevertheless, even though fundoscopy is often used as a screening method in cases of suspected increase in ICP, the grading scale is not widely applicable or accepted.

The technique itself is limited to the abilities of the examiner, as well as the circumstances surrounding the examination, the examiner requiring good visualization of the optic disc to be able to detect papilledema [ ]. Furthermore, since the process of optic disc swelling in cases of raised ICP takes time, the technique cannot be applied in emergency situations with sudden increases in ICP, such as, trauma [ ].

ICP monitoring techniques are multiple and diverse. Nevertheless, before choosing the technique to apply in critical care, several factors need to be considered; the precision of measurements made, the cost of the device as well as the possible complications and mechanical problems associated with the individual techniques. In regards to precision of measuring accurate ICP values, EVDs are considered the gold standard, closely followed by microtransducers, which measure ICP almost just as accurately [ 69 , 81 ].

The noninvasive techniques have their greatest shortcomings in this field. At present, none of the above-mentioned noninvasive techniques are accurate enough to be used in a critical intensive care setting. On the other hand, the noninvasive techniques have their advantages in completely avoiding complications such as hemorrhages and infections, which are often associated with the invasive techniques.

This is an intensely debated issue, especially given the fact that general guidelines for ICP monitoring are not widely accepted, resulting in variations for application of invasive ICP monitoring among hospitals [ 8 , 22 , 46 ]. One could fear that a too liberal approach for invasive ICP monitoring could result in unnecessary worsened clinical patient outcome, without the monitoring itself having any relevance to the way these patients are treated.

A significant number of these patients will develop systemic or cerebral infections, with subsequent risk of increased mortality and morbidity, for example, hydrocephalus, infarcts, epilepsy, or cranial nerve palsy [ ]. As Dasic et al. One would like to think that this relative simple technology would be more reliable than the more complex microtransducers.

In most part, the relatively high percentage of malfunctioning EVDs is due to the EVD being placed intraparenchymaly or blocked with pieces of brain matter and blood clots [ 67 — 69 ]. For the reviewed noninvasive techniques, there are several patient categories for which the measuring technique cannot be applied in critical care practice. In addition to the equipment comes also the subsequent cost of maintaining and replacing it. The noninvasive techniques require only the single expense of purchasing the device, after which the devices can be applied multiple times without further costs apart from wages and maintenance.

To summarize, economically and complication wise, the noninvasive techniques are favored. However, considering the high number of patients where noninvasive techniques cannot be applied, and more importantly, the low accuracy of the ICP measurements undertaken, the noninvasive techniques are less favorable. The current noninvasive techniques are simply not accurate enough to replace the traditional invasive techniques. This leaves us with the choice between EVDs and microtransducers.

Precision wise, there is not a great difference between these two techniques, despite the fact that most microtransducers cannot be recalibrated. However, in this context it is important to point out that the Camino MicroSensor has problems with a large zero drift [ 74 , 75 ].

Economically, microtransducers are more expensive, but apparently they carry a lower rate of postoperative infections. EVDs, on the other hand, have the advantage that they can be used for drainage of CSF and administering of drugs intrathecally. Table 3 summarizes the results. Whether EVD or microtransducers is the optimal ICP measuring technique is a difficult question to answer unambiguously, as both have advantages and disadvantages as discussed above.

Both can, therefore, be regarded as good options when ICP monitoring is needed. But when is ICP monitoring needed in critical care? As mentioned in the background paragraph, there are no general guidelines. A thorough evaluation of the literature is outside the scope of this paper, but we will comment briefly on the topic. Stein et al. However, most of the reviewed studies are of a methodologically limited quality. A large part of the evidence advocating ICP monitoring originates from the late nineteen seventies and early eighties [ — ], but these studies are of weaker methodological design.

Current studies reporting better survival and outcome with ICP monitoring include Patel et al. However, several other studies have reached the opposite conclusion, indicating worse outcome as a consequence of ICP monitoring and CPP-oriented therapy [ 46 , — ]. Nevertheless, to this date, no prospective randomized study of the possible benefits of ICP monitoring has been done. It is apparent today that additional neuromonitoring modalities should supplement ICP in the critical care setting, thereby increasing patient safety by more accurately guiding treatment interventions in terms of type, aggressiveness and duration, including controlled tapering [ ].

To answer the first question, we can conclude that both EVD and microtransducers are good technologies for ICP monitoring. Both are accurate in ICP monitoring, but have risks of complications in the form of postoperative hemorrhage and infection.

Which of these modalities is preferable, must ultimately be decided by the individual clinician and department.

To answer the second question, we conclude that noninvasive techniques lack the accuracy of their invasive counterparts. Additionally, the noninvasive ICP monitoring cannot be carried out on a large percentage of patients due to anatomical variations, leading us to conclude that current noninvasive techniques cannot be used as an alternative to the invasive techniques. Raboel et al.

This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors. Read the winning articles. Journal overview. Special Issues. Raboel , 1 J. Bartek, 1,2 M. Andresen , 1 B. Bellander, 2 and B. Academic Editor: John F.

Received 02 Dec Revised 28 Feb Accepted 27 Mar Published 08 Jun Abstract Monitoring of intracranial pressure ICP has been used for decades in the fields of neurosurgery and neurology. Introduction The Scottish anatomist Alexander Monro first described the intracranial pressure in [ 1 , 2 ]. Figure 1. Your doctor will carefully analyze the information obtained from this procedure and consider it along with data from other tests, such as eye examination, shunt studies, MRI or CT scans.

This process can take up to a week. Complex cases need to be discussed at the weekly case conference to provide the best course of treatment. Contact us or find a patient care location. Privacy Statement. Non-Discrimination Notice. All rights reserved. Skip Navigation.

I Want To During ICP monitoring on the ward outside the intensive care unit , we encourage your child to carry on with everyday activity as far as possible. However, as with all procedures, there are a few potential problems you should know about. Bleeding and infection is always a risk with any procedure that breaks the skin. The nurses will check the site where the ICP bolt is inserted regularly. There is also a small chance that a small amount of cerebrospinal fluid could leak from the insertion site.

Again, this will be checked regularly, but if your child develops a headache, please tell the nurses. In most cases, this will be due to the procedure itself rather than any CSF leakage and can be treated with pain relief medicines.

Occasionally, monitoring may need to last for a few days if enough information has not been recorded. A hollow screw is inserted through a hole drilled in the skull.

It is placed through the membrane that protects the brain and spinal cord dura mater. This allows the sensor to record from inside the subdural space. An epidural sensor is inserted between the skull and dural tissue. The epidural sensor is placed through a hole drilled in the skull.

This procedure is less invasive than other methods, but it cannot remove excess CSF. Lidocaine or another local anesthetic will be injected at the site where the cut will be made. You will most likely get a sedative to help you relax. Most of the time, this procedure is done when a person is in the hospital intensive care unit. If you are awake and aware, your health care provider will explain the procedure and the risks.

You will have to sign a consent form. If the procedure is done using general anesthesia , you will be asleep and pain-free. When you wake up, you will feel the normal side effects of anesthesia. You will also have some discomfort from the cut made in your skull. If the procedure is done under local anesthesia, you will be awake. Numbing medicine will be injected to the place where the cut is to be made. This will feel like a prick on your scalp, like a bee sting. You may feel a tugging sensation as the skin is cut and pulled back.