ICP monitoring--current status and future directions

Bedside ultrasound as a simple non-invasive method of assessing intracranial pressure in a limited resource setting

Introduction

Increased intracranial pressure is usually measured with invasive methods that are not practical in resource-limited countries. However, bedside ultrasound, a non-invasive method, measures the optic nerve sheath diameter and could be a safe and accurate alternative to measure intracranial pressure, even in children.

Case report

We report a case of a 15-year old patient who presented with severe headache, projectile vomiting, and neck pain for two months. The bedside ultrasound showed a 10 mm optic nerve sheath diameter and a Computed Tomography scan of her brain revealed obstructive hydrocephalus secondary to a mass in the fourth ventricle. After intervening, we were able to monitor the decrease in her optic nerve sheath diameter with ultrasound.

Conclusion

Performing invasive procedures continues to be a challenge in the resource limited setting. However, bedside ultrasound can be a useful tool in emergency centres for early detection and monitoring of intracranial pressure.

Intracranial Pressure Increases During Rewarming Period After Mild Therapeutic Hypothermia in Postcardiac Arrest Patients

Elevation of intracranial pressure (ICP) may worsen brain injury and neurological outcome. Studies on the use of therapeutic hypothermia (TH) for traumatic brain injury suggests that rapid rewarming from TH is associated with elevated ICP and poorer outcomes. However, few studies describe the time course of ICP changes during TH/rewarming after cardiac arrest (CA). In this study, we observed the changes in ICP during mild TH and rewarming after CA. Secondarily, we examined whether ICP is related to outcome. We studied comatose patients resuscitated from CA, who were treated with TH and who had ICP monitored. Target core temperature was 34°C for 24 h and target rewarming rate was 0.25°C/h. ICP and cerebral perfusion pressure (CPP) were monitored during the period. Outcome was rated as cerebral performance category. In nine patients, ICP increased during TH and rewarming (6.0 [4.0-9.0] mmHg to 16.0 [12.0-26.0] mmHg, p = 0.008). CPP did not change during the period (83.3 [80.1-91.0] mmHg to 74.3 [52.0-87.3] mmHg). Higher ICP was associated with worse outcomes (p = 0.009). All the cases with ICP >25 mmHg or CPP <40 mmHg died. Major ICP increment was observed during the rewarming period, although, some increase of ICP occurred even during the mild TH. ICP increment was higher in patients with worse outcomes.

A conceptual approach to managing severe traumatic brain injury in a time of uncertainty

Current controversies in the literature suggest that a reassessment of the current management of severe traumatic brain injury (sTBI) is necessary. This article presents a conceptual framework toward individualizing sTBI treatment with respect to targeting thresholds and strategies on the basis of known physiologic processes and available monitors. Intracranial pressure (ICP) is modeled as an epiphenomenon of cerebral compliance and herniation tendency, as well as cerebral ischemia. By combining serial neurological examinations, imaging studies, and ICP measurements (values, trends, and area-under-the-curve calculations) over time, evidence can be accrued on the necessity of maintaining ICP at a given threshold in the realm of physical changes in the brain. Similarly, by collecting and trending clinical, imaging, and monitoring data on the status of cerebral blood flow, the balance of oxygen consumption and delivery, and the status of cerebral static pressure autoregulation, and analyzing them with respect to measured parameters, such as blood pressure, ICP, and cerebral perfusion pressure, one can attempt to fine-tune these variables as well. Such individualization of management optimizes the possibility of successfully treating demonstrated pathophysiological processes while avoiding unnecessary interventions and treatment toxicity. Monitor values must not be seen as targets but rather as indicators of targetable pathology.

Prospective study of methodological issues in intracranial pressure monitoring in patients with hydrocephalus

OBJECT

Continuous intracranial pressure (ICP) monitoring is performed in selected patients with hydrocephalus to determine whether shunt placement is required. The mean ICP is usually calculated from end-hour readings manually recorded by nurses. The aim of this study was to evaluate the accuracy of manual recordings by comparing nurses' end-hour ICP readings with those of an online computerized ICP monitoring system that records one ICP value per second.

METHODS

Continuous ICP monitoring was performed using a fiberoptic extradural sensor in 115 patients with hydrocephalus of different origins. A notebook computer was connected to an ICP monitor and was programmed to register one ICP value per second. In all patients, mean ICP values were calculated from data recorded manually by nurses at the end of every hour and from data recorded by the computer within the preselected time period. The two methods were compared using correlation analysis and the Bland and Altman method. The median number of ICP values noted manually by the nurses in each patient was 17 (interquartile range 15-18 readings), and that recorded by the software was 61,200 (interquartile range 54,000-64,800 readings). The correlation coefficient of the mean ICP values recorded by both methods was r = 0.99 (p < 0.001). The Bland and Altman analysis revealed a mean difference of 0.3 +/- 1.26 mm Hg between the two methods and that they were equally valid with all mean ICP values.

CONCLUSIONS

The recording of end-hour ICP values by nurses is an accurate method of calculating the mean ICP after prolonged ICP monitoring in patients with hydrocephalus.

The effect of cerebrospinal fluid drainage on cerebral perfusion in traumatic brain injured adults

Cerebrospinal fluid drainage is a first line treatment used to manage severely elevated intracranial pressure (> or = 20 mm Hg) and improve outcomes in patients with acute head injury. There is no consensus regarding the optimal method of cerebrospinal fluid removal. The purpose of this investigation was to determine whether cerebrospinal fluid drainage decreases intracranial pressure and improves cerebral perfusion and to identify factors that impact treatment effectiveness. This study involved 31 severely head injured patients. Intracranial pressure and other indices of cerebral perfusion (cerebral perfusion pressure, cerebral blood flow velocity, and regional cerebral oximetry) were measured before, during, and after cerebrospinal fluid drainage. Arterial and jugular venous oxygen content was measured before and after cerebrospinal fluid drainage. Patients underwent three randomly ordered cerebrospinal fluid drainage protocols that varied in the volume of cerebrospinal fluid removed (1 mL, 2 mL, and 3 mL) for a total of 6 mL of cerebrospinal fluid removed. There was a significant change in the intracranial pressure from a mean at baseline of 26.1 mm Hg (SD = 4.4) to 22.1 mm Hg immediately after drainage. One third of patients experienced a decrease in the intracranial pressure below 20 mm Hg; in two patients the intracranial pressure dropped less than 1 mm Hg. The following factors predicted 61.5% of the variance in the responsiveness of intracranial pressure to drainage: vecuronium hypothermia, baseline cerebral perfusion pressure and acuity of illness. Cerebrospinal fluid drainage provides a transient decrease in intracranial pressure without a measurable improvement in other indices of cerebral perfusion.

The Brain Trauma Foundation. The American Association of Neurological Surgeons. The Joint Section on Neurotrauma and Critical Care. Indications for intracranial pressure monitoring

ICP monitoring per se has never been subjected to a prospective randomized clinical trial (PRCT) to establish its efficacy (or lack thereof) in improving outcome from severe head injury. Hence, there are insufficient data to support its use as a standard. However, there is a large body of published clinical experience that indicates that ICP monitoring (1) helps in the earlier detection of intracranial mass lesions, (2) can limit the indiscriminate use of therapies to control ICP which themselves can be potentially harmful, (3) can reduce ICP by CSF drainage and thus improve cerebral perfusion, (4) helps in determining prognosis, and (5) may improve outcome. ICP monitoring is therefore used by most head injury experts in the United States and is accepted as a relatively low-risk high-yield, modest cost intervention. Comatose head injury patients (GCS 3-8) with abnormal CT scans should undergo ICP monitoring. Comatose patients with normal CT scans have a much lower incidence of intracranial hypertension unless they have two or more of the following features at admission: age over 40, unilateral or bilateral motor posturing, or a systolic blood pressure of less than 90 mm Hg. ICP monitoring in patients with a normal CT scan with two or more of these risk factors is suggested as a guideline. Routine ICP monitoring is not indicated in patients with mild or moderate head injury. However, it may be undertaken in certain conscious patients with traumatic mass lesions at the discretion of the treating physician.

Magnetic resonance imaging with gadolinium DTPA enhancement in patients with acute head injury

Gadolinium-enhanced magnetic resonance (MR) imaging in patients with acute head injury was conducted to study if contrast extravasation was associated with development of hemorrhagic lesions. A series of 60 head-injured patients were admitted to our emergency unit. Computerized tomography (CT) scans and skull x-ray films were taken as rapidly as possible after hospitalization. Injury severity on admission was evaluated using the Glasgow Coma Scale (GCS) score, motor score, and pupillary examination, while overall outcome was assessed with the Glasgow Outcome Scale (GOS) 3 months after injury. Of all patients admitted, MR imaging with gadolinium enhancement was performed in 18 patients who were at high risk of developing hemorrhagic lesion within 6 h after injury. In these patients we investigated whether contrast extravasation was associated with development of hemorrhagic lesions. All 18 patients presented abnormal findings on their admission CT scans. Admission GCS score in those patients who underwent MR imaging with gadolinium enhancement was 13 or more in 12 patients, 9-12 in four patients, and 8 or less in two patients. Fourteen of 18 patients showed contrast extravasation, corresponding with an evolution of lesion size. Nine of 14 patients who demonstrated extravasation of the contrast medium required surgical treatment. The results of the current study suggest that extravasation of contrast medium indicates a continuance of posttraumatic bleeding. Thus, MR imaging with gadolinium enhancement in acutely head-injured patients may constitute a reasonable strategy for predicting the development of hemorrhagic lesions.

Brain oxygen tension in severe head injury

OBJECTIVE

Ensuring adequate cerebral oxygenation and perfusion is of fundamental importance in the treatment of patients with acute cerebral disorders. Online continuous monitoring of brain oxygenation is possible with a parenchymal microelectrode that measures local brain oxygen tension. The ultimate question is whether therapeutic approaches can be targeted on the basis of such monitoring. Before this question can be addressed, the technique requires validation in the clinical setting. The frequency of occurrence of low values and its relation to outcome need to be established.

METHODS

One hundred one comatose head-injured patients (Glasgow Coma Scale score < or = 8) were studied. Local brain oxygen tension probes were inserted in an undamaged part of the frontal region. Patients were treated in conformance with the European Brain Injury Consortium guidelines. Outcome at 6 months was determined by Glasgow Outcome Scale score.

RESULTS

Early brain tissue hypoxia was frequently observed, despite aggressive treatment for intracranial pressure and cerebral perfusion pressure. Values lower than 15 mm Hg, for a duration longer than 30 minutes, were observed in 57 patients. Values lower than 10 mm Hg in 42 patients, and lower than 5 mm Hg in 22 patients, were observed during the first 24 hours. Depth and duration of tissue hypoxia were related to outcome and proved to be an independent predictor of unfavorable outcome and death.

CONCLUSION

Monitoring the partial oxygen pressure of local brain tissue is a safe and reliable method for regulating cerebral oxygenation. Because brain tissue hypoxia occurs frequently and is significantly related to poor outcome, future efforts should be aimed at the treatment of brain tissue hypoxia. The effects of such brain hypoxia-targeted treatment need to be established in a multicenter study.

ICP monitoring in the rat: comparison of monitoring in the ventricle, brain parenchyma, and cisterna magna

Various methods of continuous intracranial pressure (ICP) monitoring during experimental procedures in the rat have been described. However, no systematic comparison of ICP monitoring in the ventricle, brain parenchyma, and cisterna magna has been reported. Since accurate and reliable ICP measurements are important in experimental models of traumatic brain injury, the present study was conducted to compare simultaneous ICP measurements from ventricular, cisterna magna, and intraparenchymal monitors during ICP changes. Subdural hematoma was produced by infusion of 0.3 ml of autologous blood into the subdural space over 6 min. The ventricular and the intraparenchymal fiberoptic catheter produced reliable and comparable pressure recordings, that did not statistically differ (p = 0.4), throughout the one hour monitoring time. In contrast, the cisterna magna catheter was less reliable and produced significantly lower readings throughout the monitoring time (p<0.001). The intraparenchymal device produced greater cortical damage than the ventricular catheter. In conclusion, ventricular ICP monitoring is the preferred method under these circumstances, since it is accurate and induces least brain damage.

ICP measurement accuracy: the effect of temperature drift. Design of a laboratory test for assessment of ICP transducers

Intracranial pressure (ICP) monitoring has become the mainstay of multimodal neuromonitoring of comatous patients after head injury. In the presence of rising ICP and faced with pressures, difficult to control, aggressive measures, such as hypothermia may be used. The ICP readings should not be influenced by temperature changes. A laboratory test was designed to simulate temperature variations between 20 degrees C and 45 degrees C at different pressure levels under physiological conditions. Five types of transducers were examined: Epidyn Braun Melsungen, ICT/B-Titan Gaeltec, Camino-OLM-110-4B, Codman MicroSensor ICP-Transducer, Neurovent ICP transducer Rehau Ag+Co. Tests were performed at 6 different pressure levels between 0 mmHg and 50 mmHg. The results show very low drifts of less than 0.15 mmHg degree C-1 for Codman, Epidyn and Neurovent. Gaeltec and Camino exhibited higher drifts of 0.18 mmHg and 0.2 mmHg degree C-1 respectively. Within the temperature range from 35 degrees C to 42 degrees C all probes tested show insignificant temperature drift. Whether these results also apply to other types of transducers needs further evaluation. Problems and requirements related to the design of a laboratory test for the in vitro assessment of ICP transducers are discussed in detail.

[Slow pressure waves during intracranial hypertension]

Intracranial pressure waves include fast waves (pulse and respiration) and slow waves. Only the latter are considered here. Since the definition of three wave types in the pioneering works of Janny (1950) and Lundberg (1960), their study of frequential characteristics shows they are included in a spectrum where three contiguous frequency bands are individualised: the B wave band (BW) between 8 x 10(-3) Hz and 50 x 10(-3) Hz; the Infra B band (IB) below 8 x 10(-3) Hz; and the Ultra B band (UB) beyond 50 x 10(-3) Hz to 200 x 10(-3) Hz. The origin of these waves is vascular and some may be physiological. They are probably generated by central neuro-pacemakers and/or cyclic phenomena of cerebral autoregulation. They are linked with slow peripheral arterial pressure waves, with biological rhythms and with biomechanics and vasomotricity in the craniospinal enclosure. They are pathological for the slowest (IB), particularly if they are plateau waves, but the physiologic-pathologic boundary is not yet established for each type of slow waves. They can cause severe consequences if they result in major cerebral perfusion pressure changes, and if they induce or worsen herniations.

Evolving brain lesions in the first 12 hours after head injury: analysis of 37 comatose patients

From January 1, 1990, to April 30, 1994, 412 patients were admitted to our intensive care unit in coma after head injuries. Our study group consisted of 37 patients who were retrospectively identified as harboring lesions or developing new lesions within a 12-hour period from the time of admission. We defined the evolution of a lesion as an increase or decrease in the size of an already present hematoma or as the appearance of a totally new lesion. There were 25 male and 12 female patients (mean age, 34.9 yr), and the cause of trauma was road traffic accidents in 32 patients. Nine patients presented with shock, and six had evidence of abnormal coagulation at admission. Patients were divided into two different groups. In Group 1, 15 patients harbored lesions that evolved toward reabsorption. In Group 2, 22 patients harbored hematomas that evolved toward lesions requiring surgical removal. Fifteen of these patients had initial diagnoses of diffuse injury that evolved in this manner, whereas the remaining seven patients had already been operated upon and had developed second, noncontiguous, surgical lesions. Patients with lesions that required surgical evacuation had their computed tomographic (CT) scans obtained earlier and had a higher incidence of clinical deterioration. There was a significant difference in the evolution of the different lesions (P < 0.001), with subdural hematomas being more prone to reabsorption and intracerebral and extradural hematomas being more likely to increase in size or to appear as new lesions. Second CT scans were obtained because of clinical deterioration in 10 patients and because of increase in intracranial pressure in 5 patients. Scheduled CT scans were obtained in 13 patients, whereas in the remaining 9 patients, the diagnosis emerged from a combination of scheduled CT scans and intracranial pressure monitoring. There was a trend toward a poorer result among the patients with clinical deterioration, which, however, was not significant. A significant proportion of post-traumatic patients, particularly those who are unconscious, harbor early evolving intracranial lesions. When the first CT scan is performed within 3 hours after injury, a CT scan should be repeated within 12 hours.

Highlighting intracranial pressure monitoring in patients with severe acute brain trauma

Intracranial pressure (ICP) monitoring was carried out in 100 patients with severe acute brain trauma, primarily by means of a subarachnoid catheter. Statistical associations were evaluated between maximum ICP values and: 1) Glasgow Coma Scale (GCS) scores; 2) findings on computed tomography (CT) scans of the head; and 3) mortality. A significant association was found between low GCS scores (3 to 5) and high ICP levels, as well as between focal lesions on CT scans and elevated ICP. Mortality was significantly higher in patients with ICP > 40 mm Hg than in those with ICP < or = 20 mm Hg.

Bedside measurement of the third ventricle's diameter during episodes of arising intracranial pressure after head trauma. Using transcranial real-time sonography for a non-invasive examination of intracranial compensation mechanisms

Using transcranial real-time sonography, changes in the axial diameter of the third ventricle during manoeuvres, which increased intracranial pressure (ICP), were measured in 28 patients with moderate to severe head injury. The measurements were correlated with ICP measured by epidural pressure monitoring. We observed reductions in diameter ranging from 0.3 to 1.1 mm with rises in intracranial pressure of at least 5 mm in 22 patients of whom only one died. In 6 additional patients, no changes in diameter were seen, and 5 of the 6 died. We interpret that poor outcome as a measurable inability for the brain to expel cerebrospinal fluid into extracerebral compartments during increased ICP. Transcranial real-time sonography may provide additional information about intracranial cerebral fluid dynamics and compliance.

Extracranial complications of severe head injury

In order to define the role of intracranial and extracranial complications in determining outcome from severe head injury, 734 patients from the Traumatic Coma Data Bank were analyzed. Nine classes of intracranial and 13 classes of extracranial complications occurring within the first 14 days after admission were analyzed, while controlling for age, admission Glasgow Coma Scale motor score, early hypoxia or hypotension, and severe extracranial trauma. Outcome for survivors was based on the last recorded Glasgow Outcome Scale score, obtained a median of 521 days after injury. Intracranial complications did not significantly alter outcome for the study group. Of the extracranial complications, pulmonary, cardiovascular, coagulation, and electrolyte disorders occurred most frequently at 2 to 4 days. Infections developed later, peaking at 5 to 11 days. Gastrointestinal, renal, and hepatic complications followed no specific time course. Electrolyte abnormalities were the most frequent occurrence (59% of patients) but did not alter outcome. Pulmonary infections (41%), shock (29%, systemic blood pressure < or = 90 mm Hg for 30 minutes or more), coagulopathy (19%), and septicemia (10%) were significant independent predictors of an unfavorable outcome. Backward-elimination, stepwise logistic regression modeling indicated that the estimated reduction of unfavorable outcome was 2.9% for the elimination of pneumonia, 3.1% for coagulation disturbances, 1.5% for septicemia, and 9.3% for shock. These data suggest that extracranial complications are highly influential in determining the outcome from severe head injury and that significant improvements in outcome in a sizeable proportion of patients could be accomplished by improving the ability to prevent or reverse pneumonia, hypotension, coagulopathy, and sepsis.

Cerebrospinal fluid physiology and the management of increased intracranial pressure

Increased intracranial pressure can result in irreversible injury to the central nervous system. Among the many functions of the cerebrospinal fluid, it provides protection against acute changes in venous and arterial blood pressure or impact pressure. Nevertheless, trauma, tumors, infections, neurosurgical procedures, and other factors can cause increased intracranial pressure. Both surgical and nonsurgical therapeutic modalities can be used in the management of increased intracranial pressure attributable to traumatic and nontraumatic causes. In patients with cerebral injury and increased intracranial pressure, monitoring of the intracranial pressure can provide an objective measure of the response to therapy and the pressure dynamics. Intraventricular, intraparenchymal, subarachnoid, and epidural sites can be used for monitoring, and the advantages and disadvantages of the various devices available are discussed. With the proper understanding of the physiologic features of the cerebrospinal fluid, the physician can apply the management principles reviewed herein to minimize damage from intracranial hypertension.