Traumatic brain injury (TBI) is one of the major causes of death and disability where limited improvement in outcome is achieved despite the advances of medical and surgical care.8131620) The Brain Trauma Foundation (BTF) established guidelines [American Association of Neurological Surgeons (AANS), ver. 2007]7) on the use of intracranial pressure (ICP) monitoring in TBI, but its use has not been popular among neurosurgeons for various clinical reasons.16) Many neurosurgeons find insertion of ICP monitoring devices unfamiliar and cumbersome, and procedures of ICP monitoring may put the hemodynamically unstable patient at additional risk.30) Despite the debate on the usefulness of ICP monitoring, however, a future demand for evidence-based medical care and surgical management of TBI creates a need for such monitoring.

Various types of ICP monitoring devices are available for clinical use. Commonly used intraparenchymal ICP monitors are simpler in terms of insertion, but less accuracy and difficulty in baseline adjustment are known drawbacks of this type.26) Although insertion of intraventricular ICP monitors is technically more difficult, ICP measurements are more accurate and therapeutic drainage of cerebrospinal fluid (CSF) to lower elevated ICP is possible.16) Known drawbacks of conventional ventricular ICP monitoring devices include overdrainage or underdrainage of CSF which may reduce the reliability of measurements and risk patient safety.131) The LiquoGuard® system (Möller Medical GmbH, Fulda, Germany) is a new ventricular-type monitoring device that facilitates ICP-controlled or volume-controlled drainage of CSF. The aim of this study is to report the authors' experience with the LiquoGuard® ICP monitoring system, as well as the clinical safety, usefulness, and limitation of this device in the management of patients with TBI.

Ten patients underwent ICP monitoring with the LiquoGuard® monitoring system. Five (50%) patients were male, and 5 (50%) were female. The mean age was 46.4 years with a range of 18 to 68 years. The diagnoses of patients were as listed in Table 1. The average GCS on admission was 6.4 (range, 4-12). On the patients' initial CT scans, the average midline shift was 1.4 cm.

The mean duration of ICP monitoring was 6.9 days (range, 1.6-13.8 days) (Table 2). ICP readings were recorded every 6 seconds with a mean 82,718 records per patient (range, 22,722-163,679). Mean initial ICP was 16.4 mm Hg (range, 4.8-32.5 mm Hg) and the average ICP across the total duration of monitoring was 15.5 mm Hg (range, 10.5-23.4 mm Hg). Two patients underwent decompressive surgery after cessation of ICP monitoring due to intolerable intracranial hypertension. The mean amount of drained CSF was 29.2 cc/day (range, 0-90.8 cc/day). Among the 10 patients, no CSF was drained in 4 patients. During the whole duration of monitoring, 7 (70%) patients showed 1 or 2 episodes of abnormal ICP measurements (Figure 2). The 6 months modified Rankin Scale (mRS) was good (mRS of ≤3) in 5 (50%) patients and poor (mRS ≥4) in the other 5 (50%) patients. Correlational analyses of the duration of ICP monitoring, initial ICP, mean ICP, amount of drained CSF, and 6 months mRS revealed that only the duration of ICP monitoring was significantly related to the 6 months mRS outcome (p=0.05). No patient showed complications associated with ICP monitoring in our series.

Besides the direct injury to the brain, intracranial hypertension often presents as the major clinical problem following TBI.24) Pathologically elevated ICP reduces cerebral perfusion pressure and causes widespread secondary damage by cerebral ischemia in the vital brain structures.23) Recognition of ICP in TBI patients is crucial regarding choice of therapy, and ICP-dependent treatment strategies are reported to benefit patient outcomes.910)

In 2007, the BTF recommended ICP monitoring for all severe TBI patients with a GCS between 3 to 8 and an abnormal CT scan. Although some authors have questioned the risk associated with ICP monitoring, numerous reports describe its benefit in producing favorable patient outcomes, supporting more widespread use of this technique.34591011) Moreover, ICP monitoring in the future will be essential for the practice of evidence-based medicine and will help improve neurotrauma critical care.

There are various types of U. S. Food and Drug Administration-approved ICP monitoring devices available for use. They can be classified according to the location of the sensor probe, i.e., intraparenchymal, ventricular, subdural, and epidural.33) Of these, intraparenchymal devices are the most frequently used and studied as they are simple to use and their measurements directly reflect the pressure in the cerebral cortex.152526) However, intraparenchymal devices also carry the known limitations of zero drift and mechanical device failure.22225262732) Zero drift occurs due to the inability of the device to be recalibrated in relation to atmospheric pressure and was reported to occur in 50 to 60% of cases, with drift greater than 5 mm Hg in about 20% of cases.21427) This device is also prone to mechanical failure because the fiber-optic transducers and cables are susceptible to excessive kinking or bending.25) The subdural and epidural monitors are similar to the intraparenchymal type and may be useful in specific circumstances, but their measurements are known to be less reliable than the intraparenchymal type due to their placement locations.628)

Intraventricular ICP monitors are the most accurate and provide the most reliable ICP measurements.61217) However, a fluid-filled system is necessary for accurate ICP measurement, and limitations exist when the patient's ventricles are compressed or slit, which is frequently observed in patients with TBI.283033) In addition, correct intraventricular placement of the catheter is difficult in these cases. Despite the limitations of intraventricular monitoring, it is the only monitoring technique that allows simultaneous drainage of CSF for lowering ICP.61728)

Traditional intraventricular monitors use tip-sensors at the end of the ventricular catheter for measurement of ICP. The ventricular catheter and sensor are connected to a monitor for ICP measurement and a chamber, which is leveled to a reference point, for drainage of CSF. The disadvantage of this system lies in the hydraulic drainage of CSF, in which overdrainage or underdrainage is possible.131) Overdrainage or underdrainage frequently occurs when a patient is being transferred for radiologic study or when a patient is coughing. Frequent leveling of the CSF chamber also is needed when a patient's ICP changes since overdrainage can lead to ventricle collapse and inaccurate ICP measurements.

The LiquoGuard® system is designed to overcome the disadvantages of conventional intraventricular monitors. Firstly, the use of a fluid pump controls the drainage of CSF in preset pressure zones, thereby minimizing the risk of underdrainage or overdrainage. Thus, neurosurgeons and nursing personnel can reduce the time and effort spent leveling the drip chamber, and drainage of CSF is within the expected amount. Secondly, a fluid-filled closed system reduces CSF contact with air, which lessens the possible risk of infection. Thirdly, the LiquoGuard® system uses 2 pressure transducers, which allows for a double-check of unrecognized sensor malfunctions. The main console has an alarm system that can be set for various monitoring circumstances, e.g., an abrupt change in pressure, a sensor malfunction, or CSF drainage status, which make early detection of catheter occlusion or intracranial changes possible. Lastly, common EVD catheters can be connected for monitoring, which enable the use of a neuronavigation system for easy insertion. Further, cost savings is achieved compared with single-use tip-sensors.

To the best our knowledge, there are only a few reports on the use of the LiquoGuard® system and only one in the field of neurosurgery.192129) Linsler et al.21) compared the results of simultaneous ICP monitoring with the LiquoGuard® system and tip-sensor intraventricular monitors in 15 patients with TBI and subarachnoid hemorrhage. They reported that the LiquoGuard® system provided adequate ICP measurements and had various advantages over tip-sensor monitors but found episodes of unreliable measurements in 2 patients due to slit ventricles. In our study, we also experienced episodes of unreliable measurements in 7 of 10 (70%) patients. In the 3 patients who did not show abnormal ICP measurements, CSF was not drained as the ICP readings were below the level of drainage pressure. We think that slit ventricles, sensor malfunctions, or inadequate manipulation of the device may underlie the high incidence of abnormal measurement episodes in the current study. In all cases, the ICP measurement returned to reasonable values within minutes to hours.

Due to the small number of patients studied, the clinical outcome of the patients did not correlate with initial ICP, mean ICP, or amount of drained CSF. Only the duration of ICP monitoring was associated with clinical outcome, which may be due to a prolonged need for monitoring in cases of poor clinical status.

Our group has previously reported on the clinical usefulness of ventricular-type monitoring in comparison with intraparenchymal-type monitoring.18) In the course of that study, we found that leveling of the CSF chamber for adequate CSF drainage was time-consuming and difficult. The use of the LiquoGuard® system reduced the drawbacks of conventional intraventricular-type monitoring, without any associated complications.

This report is only a preliminary examination of the use of the LiquoGuard® system in 10 TBI patients. A detailed study of a larger patient population may be needed to reveal the true clinical advantage of LiquoGuard® over conventional ICP monitoring devices.

From our preliminary study, the LiquoGuard® system is a versatile tool in the management of TBI patients in that its use is both reliable and feasible for ICP monitoring and therapeutic drainage of CSF. However, episodes of abnormal ICP measurements were frequently observed in patients with slit ventricles, and further study of this device may be needed under these circumstances.