CEREBRAL VASOMOTOR PARALYSIS PRODUCED BY INTRACRANIAL HYPERTENSION

Correlation of cerebral microvascular circulation with vital signs in cerebral compression and the validity of three concepts: vasodilation, autoregulation, and terminal rise in arterial pressure

Background

Vasodilation, autoregulation, and rising arterial pressure are three common concepts in cerebral compression, believed to improve cerebral blood flow to maintain the brain's nutrition. However, these concepts are unclear, unproven, and based on assumptions. This study aimed to correlate cerebral circulation with alterations of vital signs and to evaluate the above concepts based on physics and hemodynamics.

Methods

Without new animal experiments, a large amount of data: recording of vital signs, long movies of cerebral circulation, and numerous photos of histological examination and microvessels obstruction in cerebral compression in cats was studied, and only partial and preliminary results were reported in 1970. The experiments were supported by an NIH grant for head injury, done before the 1985 Institutional Animal Care and Use Committee requirement. The advent of digital technology facilitated digitizing and stepwise correlating them and evaluating the validity of the above concepts.

Results

As cerebral compression increased intracranial pressure (ICP), veins dilated, not arteries, and arterial microvessels obstructed, diminished, and stopped cerebral circulation. Simultaneously, vital signs deteriorated, and pupils became fixed and dilated. There was no evidence for what is believed as autoregulation.

Conclusion

In cerebral compression, rising ICP obstructs cerebral arterial microvessels while simultaneously deteriorating vital signs. There is no evidence for dilatation of the arteries; only veins dilate, best-called venodilation. There is no evidence of autoregulation; what occurs is a cerebral compartmental syndrome. The terminal rise of arterial pressure is the hemodynamic result of cerebral circulation cessation, overloading the aorta. None of the concepts benefit the brain's nutrition.

Critical ICP thresholds in relation to outcome: Is 22 mmHg really the answer?

PURPOSE

Intensive care for patients with traumatic brain injury (TBI) aims, among other tasks, at avoiding high intracranial pressure (ICP), which is perceived to worsen motor and cognitive deficits and increase mortality. International recommendations for threshold values for ICP were increased from 20 to 22 mmHg in 2016 following the findings in a study by Sorrentino et al., which were based on an observational study of patients with TBI of averaged ICP values. We aimed to reproduce their approach and validate the findings in a separate cohort.

METHODS

Three hundred thirty-one patients with TBI were included and categorised according to survival/death and favourable/unfavourable outcome at 6 months (based on Glasgow Outcome Score-Extended of 6-8 and 1-5, respectively). Repeated chi-square tests of survival and death (or favourable and unfavourable outcome) vs. high and low ICP were conducted with discrimination between high and low ICP sets at increasing values (integers) between 10 and 35 mmHg, using the average ICP for the entire monitoring period. The ICP limit returning the highest chi-square score was assumed to be the threshold with best discriminative ability. This approach was repeated after stratification by sex, age, and initial Glasgow Coma Score (GCS).

RESULTS

An ICP limit of 18 mmHg was found for both mortality and unfavourable outcome for the entire cohort. The female and the low GCS subgroups both had threshold values of 18 mmHg; for all other subgroups, the threshold varied between 16 and 30 mmHg. According to a multiple logistic regression analysis, age, initial GCS, and average ICP are independently associated with mortality and outcome.

CONCLUSIONS

Using identical methods and closely comparable cohorts, the critical thresholds for ICP found in the study by Sorrentino et al. could not be reproduced.

Impact of early external ventricular drainage on functional outcome after traumatic brain injury: a bicentric retrospective cohort analysis

PURPOSE

Several studies have confirmed that external ventricular drain decreases intracranial pressure (ICP) after traumatic brain injury (TBI). Considering its impact on ICP control and cerebral waste metabolites clearance, timing of external ventricular drain (EVD) insertion could improve CSF drainage efficiency. The aim of the study was to evaluate the impact of early EVD versus a later one on the 3-month outcome.

METHODS

For this retrospective cohort study conducted in two regional trauma-center (Caen CHU Côte de Nacre and Beaujon Hospital) between May 2011 and March 2019, all patients with intracranial hypertension following TBI and treated with EVD were included. We defined the early EVD by drainage within the 24 h of the hospital admission and the late EVD insertion by drainage beyond 24 h. A poor outcome was defined as a Glasgow Outcome Scale of one or two at 3 months.

RESULTS

Among the cohort of 671 patients, we analyzed 127 patients. Sixty-one (48.0%) patients had an early insertion of EVD. In the early EVD group, the mean time to insertion was 10 h versus 55 h in the late EVD group. Among the analyzed patients, 69 (54.3%) had a poor outcome including 39 (63.9%) in the early group and 30 (45.5%) in the later one. After adjustment on prognostic factors, early EVD insertion was not associated with a decrease in a poor outcome at 3-months (OR = 1.80 [0.73-4.53]).

CONCLUSION

Early insertion of EVD (<24 h) for intracranial hypertension after TBI was not associated with improved outcome at 3 months.

A Spectral Approach to Model-Based Noninvasive Intracranial Pressure Estimation

BACKGROUND

Intracranial pressure (ICP) normally ranges from 5 to 15 mmHg. Elevation in ICP is an important clinical indicator of neurological injury, and ICP is therefore monitored routinely in several neurological conditions to guide diagnosis and treatment decisions. Current measurement modalities for ICP monitoring are highly invasive, largely limiting the measurement to critically ill patients. An accurate noninvasive method to estimate ICP would dramatically expand the pool of patients that could benefit from this cranial vital sign.

METHODS

This article presents a spectral approach to model-based ICP estimation from arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) measurements. The model captures the relationship between the ABP, CBFV, and ICP waveforms and utilizes a second-order model of the cerebral vasculature to estimate ICP.

RESULTS

The estimation approach was validated on two separate clinical datasets, one recorded from thirteen pediatric patients with a total duration of around seven hours, and the other recorded from five adult patients, one hour and 48 minutes in total duration. The algorithm was shown to have an accuracy (mean error) of 0.4 mmHg and -1.5 mmHg, and a precision (standard deviation of the error) of 5.1 mmHg and 4.3 mmHg, in estimating mean ICP (range of 1.3 mmHg to 24.8 mmHg) on the pediatric and adult data, respectively. These results are comparable to previous results and within the clinically relevant range. Additionally, the accuracy and precision in estimating the pulse pressure of ICP on a beat-by-beat basis were found to be 1.3 mmHg and 2.9 mmHg respectively.

CONCLUSION

These contributions take a step towards realizing the goal of implementing a real-time noninvasive ICP estimation modality in a clinical setting, to enable accurate clinical-decision making while overcoming the drawbacks of the invasive ICP modalities.

Intracranial Pressure and Intracranial Elastance Monitoring in Neurocritical Care

Patients with acute brain injuries tend to be physiologically unstable and at risk of rapid and potentially life-threatening decompensation due to shifts in intracranial compartment volumes and consequent intracranial hypertension. Invasive intracranial pressure (ICP) monitoring therefore remains a cornerstone of modern neurocritical care, despite the attendant risks of infection and damage to brain tissue arising from the surgical placement of a catheter or pressure transducer into the cerebrospinal fluid or brain tissue compartments. In addition to ICP monitoring, tracking of the intracranial capacity to buffer shifts in compartment volumes would help in the assessment of patient state, inform clinical decision making, and guide therapeutic interventions. We review the anatomy, physiology, and current technology relevant to clinical management of patients with acute brain injury and outline unmet clinical needs to advance patient monitoring in neurocritical care.

Cardiac-gated intracranial elastance in a swine model of raised intracranial pressure: a novel method to assess intracranial pressure-volume dynamics

OBJECTIVE

Previous studies have demonstrated the importance of intracranial elastance; however, methodological difficulties have limited widespread clinical use. Measuring elastance may offer potential benefit in helping to identify patients at risk for untoward intracranial pressure (ICP) elevation from small rises in intracranial volume. The authors sought to develop an easily used method that accounts for the changing ICP that occurs over a cardiac cycle and to assess this method in a large-animal model over a broad range of ICPs.

METHODS

The authors used their previously described cardiac-gated intracranial balloon pump and swine model of cerebral edema. In the present experiment they measured elastance at 4 points along the cardiac cycle-early systole, peak systole, mid-diastole, and end diastole-by using rapid balloon inflation to 1 ml over an ICP range of 10-30 mm Hg.

RESULTS

The authors studied 7 swine with increasing cerebral edema. Intracranial elastance rose progressively with increasing ICP. Peak-systolic and end-diastolic elastance demonstrated the most consistent rise in elastance as ICP increased. Cardiac-gated elastance measurements had markedly lower variance within swine compared with non-cardiac-gated measures. The slope of the ICP-elastance curve differed between swine. At ICP between 20 and 25 mm Hg, elastance varied between 8.7 and 15.8 mm Hg/ml, indicating that ICP alone cannot accurately predict intracranial elastance.

CONCLUSIONS

Measuring intracranial elastance in a cardiac-gated manner is feasible and may offer an improved precision of measure. The authors' preliminary data suggest that because elastance values may vary at similar ICP levels, ICP alone may not necessarily best reflect the state of intracranial volume reserve capacity. Paired ICP-elastance measurements may offer benefit as an adjunct "early warning monitor" alerting to the risk of untoward ICP elevation in brain-injured patients that is induced by small increases in intracranial volume.

Measuring intracranial pressure by invasive, less invasive or non-invasive means: limitations and avenues for improvement

Sixty years have passed since neurosurgeon Nils Lundberg presented his thesis about intracranial pressure (ICP) monitoring, which represents a milestone for its clinical introduction. Monitoring of ICP has since become a clinical routine worldwide, and today represents a cornerstone in surveillance of patients with acute brain injury or disease, and a diagnostic of individuals with chronic neurological disease. There is, however, controversy regarding indications, clinical usefulness and the clinical role of the various ICP scores. In this paper, we critically review limitations and weaknesses with the current ICP measurement approaches for invasive, less invasive and non-invasive ICP monitoring. While risk related to the invasiveness of ICP monitoring is extensively covered in the literature, we highlight other limitations in current ICP measurement technologies, including limited ICP source signal quality control, shifts and drifts in zero pressure reference level, affecting mean ICP scores and mean ICP-derived indices. Control of the quality of the ICP source signal is particularly important for non-invasive and less invasive ICP measurements. We conclude that we need more focus on mitigation of the current limitations of today's ICP modalities if we are to improve the clinical utility of ICP monitoring.

Effects of pregabalin on brain edema, neurologic and histologic outcomes in experimental traumatic brain injury

Brain edema and increased intracranial pressure (ICP) are among the main causes of neurological disturbance and mortality following traumatic brain injury (TBI). Since pregabalin neuroprotective effects have been shown, this study was performed to evaluate the possible neuroprotective effects of pregabalin in experimental TBI of male rats. Adult male Wistar rats were divided into 4 groups: sham, vehicle, pregabalin 30 mg/kg and pregabalin 60 mg/kg. TBI was induced in vehicle and pregabalin groups by Marmarou method. Pregabalin was administered 30 min after TBI. Sham and vehicle groups received saline. Brain water and Evans blue content and histopathological changes were evaluated 24, 5 and 24 h after TBI, respectively. The ICP and neurological outcomes (veterinary coma scale, VCS) were recorded before, 1 h and 24 h post TBI. The results showed a significant reduction in brain water content and ICP, and a significant increase in VCS of pregabalin group (60 mg/kg) as compared to vehicle group (P < 0.05). Also, pregabalin reduced brain edema and apoptosis score as compared to vehicle group. Post TBI pregabalin administration revealed a delayed but significant improvement in ICP and neurological outcomes in experimental TBI. The underlying mechanism(s) was not determined and needs further investigation.

Progressive Brain Compression

Continuous recording of vital physiological variables and sequential MR imaging were performed simultaneously during continuous expansion of an epidural rubber balloon over the left hemisphere in anaesthetised dogs. Balloon expansion led to a progressive and slightly nonlinear rise in intracranial CSF pressures and a fall in local perfusion pressures. Changes in systemic arterial pressure, pulse rate, and respiration rate usually appeared at a balloon volume of 4% to 5% of the intracranial volume (reaction volume), together with a marked transtentorial pressure gradient and MR imaging changes consistent with tentorial herniation. Respiratory arrest occurred at a balloon volume of approximately 10% of the intracranial volume (apnoea volume), which was associated with occlusion of the cisterna magna, consistent with some degree of foramen magnum herniation. Increase in tissue water was observed beginning at approximately the reaction volume, presumably due to ischaemic oedema, due to the fall in perfusion pressures.

Cerebral spinal fluid dynamics: effect of hypoxia and implications for high-altitude illness

The pathophysiology of acute mountain sickness and high-altitude cerebral edema, the cerebral forms of high-altitude illness, remain uncertain and controversial. Persistently elevated or pathological fluctuations in intracranial pressure are thought to cause symptoms similar to those reported by individuals suffering cerebral forms of high-altitude illness. This review first focuses on the basic physiology of the craniospinal system, including a detailed discussion of the long-term and dynamic regulation of intracranial pressure. Thereafter, we critically examine the available literature, based primarily on invasive pressure monitoring, that suggests intracranial pressure is acutely elevated at altitude due to brain swelling and/or elevated sagittal sinus pressure, but normalizes over time. We hypothesize that fluctuations in intracranial pressure occur around a slightly elevated or normal mean intracranial pressure, in conjunction with oscillations in arterial Po2 and arterial blood pressure. Then these modest fluctuations in intracranial pressure, in concert with direct vascular stretch due to dilatation and/or increased blood pressure transmission, activate the trigeminal vascular system and cause symptoms of acute mountain sickness. Elevated brain water (vasogenic edema) may be due to breakdown of the blood-brain barrier. However, new information suggests cerebral spinal fluid flux into the brain may be an important factor. Regardless of the source (or mechanisms responsible) for the excess brain water, brain swelling occurs, and a “tight fit” brain would be a major risk factor to produce symptoms; activities that produce large changes in brain volume and cause fluctuations in blood pressure are likely contributing factors.

Cerebrovenous orthostatic reactivity in pathology of the craniovertebral junction (Chiari malformation)

AIM

Chiari malformation is characterized by herniation of the cerebellar tonsils into the foramen magnum, which leads to disturbance of CSF circulation through the craniovertebral junction. Orthostatic stress, which leads to the movement of SCF through the craniovertebral junction, is an adequate method to detect these disorders. It is accompanied by changes in the intracranial pressure, affecting the cerebrovenous orthostatic reactivity (CVOR), which is noninvasively assessed in patients with Chiari malformation.

MATERIAL AND METHODS

The study involved 35 patients with Chiari malformation (26 patients with Chiari I and 9 patients with Chiari II) aged 4 to 58 years (of them 12 males). Hydrocephalus was diagnosed in 4 examined patients and myelosyringosis was diagnosed in 6 patients. Transcranial Doppler sonography was used to record the venous blood flow in the tentorial sinus of the brain while changing body position on the fracture table from +90° to -30°.

RESULTS

There is significant CVOR abnormality in most patients with Chiari malformation (more than 90%), which is characterized by either increased CVOR (sometimes 5-6-fold compared to the upper normal level (considerable hyperreactivity) or complete absence of any changes during the orthostatic load (areactivity). Before surgical treatment, CVOR of patients with Chiari malformation is often characterized by areactivity, as well as a moderate or significant hyperreactivity. After surgical treatment (decompression of the foramen magnum), patients with Chiari malformation demonstrate significant normalization of the craniovertebral volumetric ratios and CVOR if often characterized by normoreactivity (in 63%) or, more rarely, moderate hyperreactivity. The rate of venous blood flow in the tentorial sinus of the brain in patients with Chiari malformation can be increased before the surgery and normalizes after surgery.

CONCLUSION

The high incidence of disturbance of CVOR (over 90%) in patients with Chiari malformation was revealed. After surgical treatment, complete normalization of CVOR was observed in more than half of these patients (63%).

Association among intracranial compliance, intracranial pulse pressure amplitude and intracranial pressure in patients with intracranial bleeds

OBJECTIVE

To investigate the association among intracranial compliance (ICC), intracranial pulse pressure amplitude and intracranial pressure (ICP) in patients with intracranial bleeds.

METHODS

Five patients with intracranial bleeds had their ICC and ICP monitored during days 1-8 after ictus. The recordings were stored as raw data files and analysed retrospectively. The parameters mean ICC, mean ICP wave amplitude and mean ICP were determined and average values were calculated in 1 hour time periods.

RESULTS

A total of 262 1 hour recordings were analysed. There was a significant correlation between mean ICC and mean ICP wave amplitude and between mean ICC and mean ICP. The mean ICP wave amplitude was significantly higher during the 1 hour periods with mean ICC<0.5 ml/mmHg and significantly lower during 1 hour periods with mean ICC 1.5-3.0 ml/mmHg. Correspondingly, in the 159 1 hour recordings with mean ICP wave amplitude> or =5.0 mmHg, mean ICC was significantly lower than in the 103 recordings with mean ICP wave amplitude<5.0 mmHg. Mean ICP was normal (i.e. <20 mmHg) in 260 of 262 (99.2%) of the 1 hour recordings; in the 49 1 hour recordings with mean ICP>15 mmHg, mean ICC was significantly lower than in the 213 recordings with mean ICP<15.0 mmHg.

CONCLUSION

In this cohort of pressure recordings, there was a strong association between ICC and intracranial pulse pressure amplitude. There also was a strong association between ICC and mean ICP, but mean ICP was normal in 260 of 262 1 hour recordings (99.2%).

Aneurysmal subarachnoid hemorrhage models: do they need a fix?

The discovery of tissue plasminogen activator to treat acute stroke is a success story of research on preventing brain injury following transient cerebral ischemia (TGI). That this discovery depended upon development of embolic animal model reiterates that proper stroke modeling is the key to develop new treatments. In contrast to TGI, despite extensive research, prevention or treatment of brain injury following aneurysmal subarachnoid hemorrhage (aSAH) has not been achieved. A lack of adequate aSAH disease model may have contributed to this failure. TGI is an important component of aSAH and shares mechanism of injury with it. We hypothesized that modifying aSAH model using experience acquired from TGI modeling may facilitate development of treatment for aSAH and its complications. This review focuses on similarities and dissimilarities between TGI and aSAH, discusses the existing TGI and aSAH animal models, and presents a modified aSAH model which effectively mimics the disease and has a potential of becoming a better resource for studying the brain injury mechanisms and developing a treatment.

Impaired pulsation absorber mechanism in idiopathic normal pressure hydrocephalus

Object

The pathophysiology of normal pressure hydrocephalus (NPH), and the related problem of patient selection for treatment of this condition, have been of great interest since the description of this seemingly paradoxical condition nearly 50 years ago. Recently, Eide has reported that measurements of the amplitude of the intracranial pressure (ICP) can both positively and negatively predict response to CSF shunting. Specifically, the fraction of time spent in a “high amplitude” (> 4 mm Hg) state predicted response to shunting, which may represent a marker for hydrocephalic pathophysiology. Increased ICP amplitude might suggest decreased brain compliance, meaning a static measure of a pressure-volume ratio. Recent studies of canine data have shown that the brain compliance can be described as a frequency-dependent function. The normal canine brain seems to show enhanced ability to absorb the pulsations around the heart rate, quantified as a cardiac pulsation absorbance (CPA), with properties like a notch filter in engineering. This frequency dependence of the function is diminished with development of hydrocephalus in dogs. In this pilot study, the authors sought to determine whether frequency dependence could be observed in humans, and whether the frequency dependence would be any different in epochs with high ICP amplitude compared with epochs of low ICP amplitude.

Methods

Systems analysis was applied to arterial blood pressure (ABP) and ICP waveforms recorded from 10 patients undergoing evaluations of idiopathic NPH to calculate a time-varying transfer function that reveals frequency dependence and CPA, the measure of frequency-dependent compliance previously used in animal experiments. The ICP amplitude was also calculated in the same samples, so that epochs with high (> 4 mm Hg) versus low (≤ 4 mm Hg) amplitude could be compared in CPA and transfer functions.

Results

Transfer function analysis for the more “normal” epochs with low amplitude exhibits a dip or notch in the physiological frequency range of the heart rate, confirming in humans the pulsation absorber phenomenon previously observed in canine studies. Under high amplitude, however, the dip in the transfer function is absent. An inverse relationship between CPA index and ICP amplitude is evident and statistically significant. Thus, elevated ICP amplitude indicates decreased performance of the human pulsation absorber.

Conclusions

The results suggest that the human intracranial system shows frequency dependence as seen in animal experiments. There is an inverse relationship between CPA index and ICP amplitude, indicating that higher amplitudes may occur with a reduced performance of the pulsation absorber. Our findings show that frequency dependence can be observed in humans and imply that reduced frequency-dependent compliance may be responsible for elevated ICP amplitude observed in patients who respond to CSF shunting.

Intracanal pressure in compressive spinal cord injury: reduction with hypothermia

Most cases of human spinal cord injury (SCI) are accompanied by continuing cord compression. Experimentally, compression results in rapid neurological decline over hours, suggesting a rise in intracanal pressure local to the site of injury. The aim of this study was to measure the rise in local intracanal pressure accompanying progressive canal occlusion and to determine the relationship between raised intracanal pressure and neurological outcome. We also aimed to establish whether hypothermia was able to reduce raised intracanal pressure. We demonstrate that, following SCI in F344 rats, local intracanal pressure remains near normal until canal occlusion exceeds 30% of diameter, whereupon a rapid increase in pressure occurs. Intracanal pressure appears to be an important determinant of neurological recovery, with poor long-term behavioural and histological outcomes in animals subject to 8 h of 45% canal occlusion, in which intracanal pressure is significantly elevated. In contrast, good neurological recovery occurs in animals with near normal intracanal pressure (animals undergoing 8 h of 30% canal occlusion or those undergoing immediate decompression). We further demonstrate that hypothermia is an effective therapy to control raised intracanal pressure, rapidly reducing elevated intracanal pressure accompanying critical (45%) canal occlusion to near normal. Overall these data indicate that following SCI only limited canal narrowing is tolerated before local intracanal pressure rapidly rises, inducing a sharp decline in neurological outcome. Raised intracanal pressure can be controlled with hypothermia, which may be a useful therapy to emergently decompress the spinal cord prior to surgical decompression.

Boxing-related head injuries

Fatalities in boxing are most often due to traumatic brain injury that occurs in the ring. In the past 30 years, significant improvements in ringside and medical equipment, safety, and regulations have resulted in a dramatic reduction in the fatality rate. Nonetheless, the rate of boxing-related head injuries, particularly concussions, remains unknown, due in large part to its variability in clinical presentation. Furthermore, the significance of repeat concussions sustained when boxing is just now being understood. In this article, we identify the clinical manifestations, pathophysiology, and management of boxing-related head injuries, and discuss preventive strategies to reduce head injuries sustained by boxers.

Arterial blood pressure vs intracranial pressure in normal pressure hydrocephalus

OBJECTIVE

To characterize the association between arterial blood pressure (ABP) and intracranial pressure (ICP) in idiopathic normal pressure hydrocephalus (iNPH) patients, and its impact on outcome of shunt surgery.

MATERIALS AND METHODS

We analyzed all 35 iNPH patients whose ABP and ICP were recorded simultaneously during 6 years (2002-2007). The static and pulsatile pressures were averaged over consecutive 6-s intervals; the moving correlations between ICP and ABP (static and pulsatile) were determined during consecutive 4-min periods to explore time-related variations.

RESULTS

Neither static nor pulsatile ABP were altered in iNPH shunt responders. Elevated pulsatile ICP, but normal static ICP, was seen in responders. The time-varying correlations of static and of pulsatile pressures were generally low, and did not differ between shunt responders/non-responders.

CONCLUSIONS

In iNPH shunt responders, static or pulsatile ABP were not altered and only pulsatile ICP was elevated.

Second-impact syndrome and a small subdural hematoma: an uncommon catastrophic result of repetitive head injury with a characteristic imaging appearance

There have been a handful of previously published cases of athletes who were still symptomatic from a prior head injury, and then suffered a second injury in which a thin, acute subdural hematoma (SDH) with unilateral hemisphere vascular engorgement was demonstrated on CT scan. In those cases, the cause of the brain swelling/dysautoregulation was ascribed to the presence of the acute SDH rather than to the acceleration/deceleration forces that caused the SDH. We believe that the brain swelling is due to "second-impact dysautoregulation," rather than due to the effect of the SDH on the underlying hemisphere. To support our hypothesis, we present 10 additional cases of acute hemispheric swelling in association with small SDHs in athletes who received a second head injury while still symptomatic from a previous head injury. The clinical history and the unique neuroimaging features of this entity on CT are described and illustrated in detail. The CT findings included an engorged cerebral hemisphere with initial preservation of grey-white matter differentiation, and abnormal mass effect and midline shift that appeared disproportionately greater than the size of the SDH. In addition, the imaging similarities between our patients and those with non-accidental head trauma (shaken-baby syndrome) will be discussed.

A dynamic nonlinear relationship between the static and pulsatile components of intracranial pressure in patients with subarachnoid hemorrhage

OBJECT

In the search for optimal monitoring and predictive tools in neurocritical care, the relationship of the pulsatile component of intracranial pressure (ICP) and the pressure itself has long been of great interest. Higher pressure often correlates with a higher pulsatile response to the heartbeat, interpreted as a type of compliance curve. Various mathematical approaches have been used, but regardless of the formula used, it is implicitly assumed that a reproducible curve exists. The authors investigated the stability of the correlation between static and pulsatile ICPs in patients with subarachnoid hemorrhage (SAH) who were observed for several hours by using data sets large enough to allow such calculations to be made.

METHODS

The ICP recordings were obtained in 39 patients with SAH and were parsed into 6-second time windows (1,998,944 windows in 197 recordings). The ICP parameters were computed for each window as follows: static ICP was defined as the mean ICP, and pulsatile ICP was characterized by mean ICP wave amplitude, rise time, and rise time coefficient.

RESULTS

The mean ICP and ICP wave amplitudes were simultaneously high or low (the expected correlation) in only approximately 60% of observations. Furthermore, static and pulsatile ICP correlated well only over short intervals; the degree of correlation weakened over periods of hours and was inconsistent across patients and within individual patients over time. Decorrelation originated with abrupt shifting and gradual drifting of mean ICP and ICP wave amplitude over several hours.

CONCLUSIONS

The relationship between the static and pulsatile components of ICPs changes over time. It evolves, even in individual patients, over a number of hours. This can be one reason the observation of high pulsatile ICP (indicative of reduced intracranial compliance) despite normal mean ICP that is seen in some patients with SAH. The meaning and potential clinical usefulness of such changes in the curves is uncertain, but it implies that clinical events result not only from moving further out on a compliance curve; in practice, the curve, and the biological system that underlies the curve, may itself change.

Diagnostic Intracranial Pressure Monitoring and Surgical Management in Idiopathic Normal Pressure Hydrocephalus

OBJECTIVE

To review our experience of managing idiopathic normal pressure hydrocephalus (iNPH) during the 6-year period from 2002 to 2007, when intracranial pressure (ICP) monitoring was part of the diagnostic workup.

METHODS

The review includes all iNPH patients undergoing diagnostic ICP monitoring during the years 2002 to 2007. Clinical grading was done prospectively using a normal pressure hydrocephalus (NPH) grading scale (scores from 3 to 15). The selection of patients for surgery was based on clinical symptoms, enlarged cerebral ventricles, and findings on ICP monitoring. The median follow-up time was 2 years (range, 0.3–6 years). Both static ICP and pulsatile ICP were analyzed.

RESULTS

A total of 214 patients underwent the diagnostic workup, of whom 131 went on to surgery. Although 1 patient died shortly after treatment, 103 of the 130 patients (79%) improved clinically. This improvement lasted throughout the observation period. The static ICP observed during ICP monitoring was a poor predictor of the response to surgery. In contrast, among 109 of 130 patients with increased ICP pulsatility (ie, ICP wave amplitude &gt;4 mm Hg on average and &gt;5 mm Hg in &gt;10% of recording time), 101 (93%) were responders (ie, increase in the NPH score of &gt;2). Correspondingly, only 2 of 21 (10%) without increased ICP pulsatility were responders. Superficial wound infection was the only complication of ICP monitoring and occurred in 4 (2%) patients.

CONCLUSION

Surgical results in iNPH were good with almost 80% of patients improving after treatment. The data indicate that improvement after surgery can be anticipated in 9 of 10 iNPH patients with abnormal ICP pulsatility, but in only 1 of 10 with normal ICP pulsatility. Diagnostic ICP monitoring had a low complication rate.

A new index derived from the cerebrovascular pressure transmission and correlated with consciousness recovery in severely head-injured intensive care patients

BACKGROUND

In patients with serious head trauma, a moderate (20-25 mm Hg) mean level of intracranial pressure (ICP) may fail to distinguish patients with a real deteriorated intracranial status from those who are stable or improving. Because of these limitations, we analyzed the ICP curve in search of other relevant information regarding cerebrovascular pressure transmission. We looked for parameters with physiological meaning extracted from spectral analysis of cerebrovascular pressure transmission and correlated with consciousness recovery in patients with severe head injuries.

METHODS

A prospective cohort study was conducted in an intensive care unit of the University Hospital, Montpellier, France, from December 2003 to December 2005. Thirty consecutive patients admitted for severe head trauma were subjected to sedatives, mechanical ventilation, and intraparenchymatous recording of ICP and were evaluated with Glasgow Outcome Scale score. Simultaneous 60-s recordings of ICP and arterial blood pressure (BP) signals, beginning as soon as possible after head trauma, were repeated until death or clinical stabilization, every 15 min, with physicians blinded to the patients' data. Spectra of ICP and BP waveforms were computed with Fourier transform. Amplitudes of cardiac and respiratory harmonics were analyzed. Cardiac (or respiratory) gain was defined as the ratio of amplitudes of cardiac (or respiratory) harmonic of ICP to BP signals and referred to as Gc and Gr, respectively.

RESULTS

Twenty of the 30 enrolled patients recovered consciousness (Glasgow Outcome Scale score = 3, 4, or 5). Gr/Gc averaged over the whole recording period performed better in discriminating consciousness recovery (area under receiver operating characteristic [ROC] curve: 0.98; 95% confidence interval [CI]: 0.91-1) than ICP (0.76; 95% CI: 0.54-0.97), cerebral perfusion pressure (0.75; 95% CI: 0.53-0.97) and Gc (0.77; 95% CI: 0.57-0.99) (P < 0.001 for each comparison). When considering the recording period 30 h posttrauma (hpt), 162 hpt, a value of Gr/Gc > or =4 was always associated with consciousness recovery, and the relative risk was equal to 9 (95% CI: 1.42-57.12).

CONCLUSIONS

Gr/Gc, which characterizes the cerebrovascular transmission, better discriminates bad evolution than high values of ICP or low values of cerebral perfusion pressure in patients with severe head trauma. A reduction in Gr/Gc ratio might be an early alarm signaling worsening intracranial hemodynamic conditions.

Anatomic compression caused by high-volume convection-enhanced delivery to the brain

OBJECTIVE

Our group has pioneered the use of gadoteridol-loaded liposomes (GDLs) in convection-enhanced delivery (CED) using real-time magnetic resonance imaging (MRI) to visualize the distribution of therapeutic agents in nonhuman primate and canine brains. We have shown that this procedure is highly predictable and safe. In the course of recent studies, however, we noted that infusion of large volumes caused local anatomic alterations, such as ventricular compression, to occur. This article reports our analysis of CED infusions into normal brains and those compromised by tumors and how monitoring the CED infusion with MRI may be helpful in preventing some complications.

METHODS

A total of 54 CED infusions using GDLs were performed in 7 canines and 10 nonhuman primates and monitored using real-time MRI. The canines, having brain tumors, received infusions of GDLs as well as a chemotherapeutic agent via CED. The nonhuman primates were normal and received GDL infusions alone. Real-time analysis of the CED infusion was performed, looking for correct catheter position and infusion reflux, leakage, and mass effect. Retrospective analysis allowed assessment of CED volume of distribution versus volume of infusion.

RESULTS

Approximately 10% of these infusions caused anatomic compression of the ventricles, especially in the canines with tumors. Reflux along the cannula and leakage of infusate into the ventricular cerebrospinal fluid or subarachnoid space were seen. Animal behavior, however, did not appear to be affected acutely or during the course of the study, and no ventricular compression was noted 2 weeks after the CED infusion on further brain imaging studies.

CONCLUSION

These findings illustrate the value of being able to monitor infusions with real-time MRI to identify phenomena such as reflux along the cannula, leakage of infusate, and ventricular compression. Especially in tumor patients, the latter could be associated with morbidity.

Management of intracranial hypertension

Effective management of intracranial hypertension involves meticulous avoidance of factors that precipitate or aggravate increased intracranial pressure. When intracranial pressure becomes elevated, it is important to rule out new mass lesions that should be surgically evacuated. Medical management of increased intracranial pressure should include sedation, drainage of cerebrospinal fluid, and osmotherapy with either mannitol or hypertonic saline. For intracranial hypertension refractory to initial medical management, barbiturate coma, hypothermia, or decompressive craniectomy should be considered. Steroids are not indicated and may be harmful in the treatment of intracranial hypertension resulting from traumatic brain injury.

Pathophysiology of traumatic brain injury

The knowledge of the pathophysiology after traumatic head injury is necessary for adequate and patient-oriented treatment. As the primary insult, which represents the direct mechanical damage, cannot be therapeutically influenced, target of the treatment is the limitation of the secondary damage (delayed non-mechanical damage). It is influenced by changes in cerebral blood flow (hypo- and hyperperfusion), impairment of cerebrovascular autoregulation, cerebral metabolic dysfunction and inadequate cerebral oxygenation. Furthermore, excitotoxic cell damage and inflammation may lead to apoptotic and necrotic cell death. Understanding the multidimensional cascade of secondary brain injury offers differentiated therapeutic options.

Management of intracranial hypertension

Effective treatment of intracranial hypertension involves meticulous avoidance of factors that precipitate or aggravate increased intracranial pressure. When intracranial pressure becomes elevated, it is important to rule out new mass lesions that should be surgically evacuated. medical management of increased intracranial pressure should include sedation and paralysis, drainage of cerebrospinal fluid, and osmotherapy with either mannitol or hypertonic saline. For intracranial hypertension refractory to initial medical management, barbiturate coma, hypothermia, or decompressive craniectomy should be considered. Steroids are not indicated and may be harmful in the treatment of intracranial hypertension resulting from traumatic brain injury.

Intracranial pressure levels and single wave amplitudes, Glasgow Coma Score and Glasgow Outcome Score after subarachnoid haemorrhage

OBJECT

To relate intracranial pressure (ICP) levels and single ICP wave amplitudes to the acute clinical state (Glasgow Coma Score, GCS) and final clinical outcome (Glasgow Outcome Score, GOS) in patients with subarachnoid haemorrhage (SAH).

METHODS

Twenty-seven consecutive patients with severe SAH had their ICP and arterial blood pressure (ABP) continuously monitored during days 1-6 after SAH. The acute clinical state could be assessed in 11 non-sedated cases using the Glasgow Coma Scale, while outcome was assessed in all cases after 6 months using the Glasgow Outcome Scale. The ICP/ABP recordings were stored as raw data files and analyzed retrospectively. For every consecutive 6 seconds time window, mean ICP, mean cerebral perfusion pressure (CPP) and the mean ICP wave amplitude were computed.

RESULTS

The GCS during days 1-6 after SAH was significantly related to the mean ICP wave amplitude, but not to the mean ICP or mean CPP. There was also a strong relationship between the mean ICP wave amplitude and GOS 6 months after SAH, with mean ICP wave amplitudes being significantly lower in those with moderate disability/good recovery, as compared with those with severe disability and death. Mean ICP was significantly higher in those who died than in the group with moderate disability/good recovery whereas mean CPP was not different between outcome groups.

CONCLUSIONS

In this small patient group the mean ICP wave amplitude during days 1-6 after SAH was related to the acute clinical state (GCS) as well as to the clinical outcome (GOS) 6 months after SAH. Similar relationships were not found for mean ICP or the mean CPP, except for a higher mean ICP in those who died than in those with moderate disability/good recovery.

Concept of "true ICP" in monitoring and prognostication in head trauma

OBJECTIVE

To propose a new coefficient, which contains information about both the absolute ICP and the position of the 'working point' on the pressure-volume curve.

METHOD

ICP was monitored continuously in 187 sedated and ventilated patients. The RAP coefficient was calculated as the running (3 minutes) correlation coefficient between slow changes in pulse amplitude and mean ICP. RAP has value 0 on the flat part of the Pressure-Volume Curve and +1 on the ascending exponential part. Then RAP decreases to zero or becomes negative when ICP increases further and affects cerebrovascular pressure-reactivity (which flattens the pressure-volume curve). Variable tICP = ICP* (1 - RAP) has been called 'trueICP'. It magnifies the critical values of ICP when cerebrovascular reactivity is exhausted and dampens those states where absolute ICP is elevated but vascular reactivity is not affected.

RESULTS

Both Mean ICP and RAP were independently correlated with outcome (ANOVA:ICP-GOS: F = 22; p < 0.00001, RAP-GOS: F = 9; p < 0.001). 'TrueICP' had stronger association with outcome: F = 28; p < 0.000001. Mortality in those patients having 'trueICP' above the threshold of 19 mm Hg was above 80%, while the mortality in those having cICP below 19 mm Hg was only 20% (F = 80; p < 10(-8)). 'TrueICP' was also suitable for continuous monitoring: sustained rise in tICP above 19 mm Hg was strongly associated with fatal complications.

CONCLUSION

The proposed variable is a powerful predictor of fatal outcome following head injury. It is sensitive to both the rising absolute ICP and the critical loss of cerebrovascular regulation.

Intracranial pressure parameters in idiopathic normal pressure hydrocephalus patients treated with ventriculo-peritoneal shunts

BACKGROUND

Although the mean intracranial pressure (ICP) is normal in patients with idiopathic normal pressure hydrocephalus (iNPH), there could possibly be alterations in their single ICP waves.

METHOD

Thirty-nine consecutive patients treated for iNPH with ventriculo-peritoneal shunts were followed prospectively with regard to clinical and radiological findings. Changes in clinical state 12 months after shunt surgery were assessed as change on a 15-3 score NPH Grading Scale, while the changes in ventricular size were assessed by linear measures. The ICP recordings were performed as part of routine pre-operative assessment, stored as raw data files, and analyzed retrospectively. The mean ICP as well as single ICP wave amplitudes were computed and analysed in consecutive 6 second time windows.

FINDINGS

Twelve months after shunt surgery, changes in NPH score of 5 or more (very significant improvement) were observed in 12 patients (31%), of 3 to 4 (significant improvement) in 6 patients (15%), of 1 to 2 (slight improvement) in 9 patients (23%) and of -4 to 0 (non-responders) in 12 patients (31%). The ventricular size did not change in any of the outcome categories. While the pre-operative mean ICP was similar between outcome groups, the mean ICP wave amplitude was significantly higher in patients improving clinically as compared to the non-responders.

CONCLUSIONS

While pre-operative mean ICP was similar, the mean ICP wave amplitudes were significantly higher in iNPH patients improving clinically after shunt treatment as compared to the non-responders.

A new method for processing of continuous intracranial pressure signals

This paper describes a new method for processing of continuous pressure signals. Continuous intracranial pressure (ICP) signals were sampled at 100 Hz, converted into digital data and processed during 6s time windows. According to a new algorithm, cardiac beat-induced single ICP waves were identified; pressure waves caused by noise in the signal were rejected for further analysis. The amplitude and latency values of the accepted single ICP waves were determined. For accepted 6s time windows, the mean ICP wave was computed as mean ICP wave amplitude and mean ICP wave latency. Mean ICP for every time window was computed according to current practice as sum of pressure levels divided by number of samples. The mean ICP wave parameters provide information about the single ICP waves that is not given by mean ICP. The method has been implemented in software to be used during online ICP monitoring, revealing mean ICP wave amplitude, mean ICP wave latency and mean ICP as numerical values every 6s. The values are presented in trend plots. Verification of correct single ICP wave identification can be done during online ICP monitoring. The clinical significance of the method was illustrated in four patients by observations that mean wave amplitudes corresponded better to the acute clinical state than the mean ICP; mean wave amplitudes could be elevated despite a normal mean ICP. In one patient with ICP and arterial blood pressure (ABP) signals monitored simultaneously with identical time reference, there was a weak correlation between mean ICP and ABP wave amplitudes. It is tentatively suggested that the mean ICP wave parameters are related to intracranial pressure-volume compensatory reserve capacity (compliance).

Assessment of childhood intracranial pressure recordings using a new method of processing intracranial pressure signals

BACKGROUND

Intracranial compliance may be more reliably predicted by the pulsatile component (pulse pressure) than the steady (mean pressure) component of intracranial pressure (ICP). A new method of processing continuous ICP signals assessing both components of ICP is described and applied to the ICP recordings of 6 pediatric cases.

METHOD

The new method was applied to each subsequent 6-second time sequence window of a continuous ICP signal. For time sequence windows including single ICP waves, the following time sequence (TS.x)-related parameters were computed: (a) mean ICP (i.e. TS.MeanP) was computed according to the currently used and known technology; (b) the mean ICP wave was computed according to the new method, characterized by mean wave amplitude (i.e. TS.MeanWavedP) and mean wave latency (i.e. TS.MeanWavedT). Cases No. 1-4 were treated for hydrocephalus and cases No. 5 and 6 for craniosynostosis.

RESULTS

In 5 children, clinical intracranial hypertension was associated with elevations of mean ICP above 15-20 mm Hg of variable durations. The ICP recordings of the 5 children with intracranial hypertension and successful outcome after surgery revealed mean wave amplitude values above 5 mm Hg. Mean wave latency was more variable, ranging between 0.10 and 0.25 s.

CONCLUSIONS

In the children with intracranial hypertension and successful outcome after surgery, mean wave amplitude was variably above 5 mm Hg. It is suggested that mean wave amplitude may be a useful parameter by more directly predicting cerebral compliance than mean ICP.

Raised Intracranial Pressure

Raised intracranial pressure is a relatively common problem facing the clinician treating neurocritically ill patients. It is a leading cause of death in patients with intracranial pathology. There is a lack of controlled clinical trials evaluating most of the therapies currently available for raised intracranial pressure. The basic pathophysiologic and clinical principles of raised intracranial pressure are discussed and the major treatment options are presented. Patients with raised intracranial pressure should be evaluated immediately with particular attention to airway and hemodynamic status. Controlled hyperventilation and hyperosmolality (using mannitol or hypertonic saline solutions) frequently are administered simultaneously. In patients with refractory elevation of intracranial pressure other therapies such as barbiturate coma and surgical interventions are available.

Admission Perfusion CT: Prognostic Value in Patients with Severe Head Trauma

PURPOSE

To assess the prognostic value of admission perfusion computed tomography (CT) in patients with severe head trauma.

MATERIALS AND METHODS

This prospective study included 130 patients with severe trauma, aged 19-86 years, admitted with a Glasgow Coma Scale score of 8 or less. They underwent perfusion CT as part of their admission CT survey. Clinical data, unenhanced cerebral CT findings, and perfusion CT scans were evaluated with respect to the Glasgow Outcome Scale (GOS) score at 3 months. Perfusion CT features were evaluated in patients with intracranial hypertension, cerebral contusions, and juxtadural hematomas. Ordered logistic regression was used to determine risk factors for an unfavorable GOS score at 3 months.

RESULTS

Perfusion CT was more sensitive than conventional unenhanced CT in the detection of cerebral contusions. Perfusion CT featured specific patterns with respect to patient outcome, with normal brain perfusion or hyperemia in patients with favorable outcome, and oligemia in patients with unfavorable outcome. The number of arterial territories with low regional cerebral blood volume at perfusion CT was an independent prognostic factor (P =.008), as were mean arterial pressure at the scene of accident (P =.083), base excess at admission (P =.002), presence of skull fractures (P =.041), and signs of herniation (P =.013) at admission unenhanced cerebral CT. Perfusion CT also showed a range of brain perfusion alterations in patients with juxtadural collections, cerebral edema, or intracranial hypertension.

CONCLUSION

Perfusion CT in patients with severe head trauma provides independent prognostic information regarding functional outcome.

What is the optimal cerebral perfusion pressure in children suffering from traumatic coma?

Head injury is a major cause of death and disability in children. Despite advances in resuscitation, emergency care, intensive care monitoring, and clinical practices, there are few data demonstrating the predictive value of certain physiological variables regarding outcome in this patient population. Mean arterial blood pressure (MABP), intracranial pressure (ICP), and cerebral perfusion pressure (CPP = MABP − ICP) are routinely monitored in patients in many neurological intensive care units throughout the world, but there is little evidence indicating that advances in care have been matched with corresponding improvements in outcome.

Nonetheless, there is evidence that hypotension immediately following head injury is predictive of early death, and many patients with these features die with clinical signs of brain herniation caused by intracranial hypertension. Furthermore, available data indicate that a minimal and a mean CPP measured during intensive care are good predictors of outcome in survivors, but a target threshold to improve outcome has yet to be defined.

Some medical management strategies can have detrimental effects, and there is now a good case for undertaking a controlled trial of immediate or delayed craniectomy. Independent outcome in children following severe head injury is associated with higher levels of CPP. The ability to tolerate different levels of CPP may be related to age, and therefore any such surgical trial would need a carefully defined protocol so that the potential benefit of such a treatment is maximized.

Monitoring of cerebral perfusion pressure during intracranial hypertension: a sufficient parameter of adequate cerebral perfusion and oxygenation?

OBJECTIVE

A cerebral perfusion pressure (CPP) oriented treatment is a widely accepted standard for patients with intracranial hypertension. In an animal model of controlled intracranial hypertension we investigated whether CPP is a reliable parameter of sufficient cerebral perfusion and oxygenation. Using near-infrared reflexion spectroscopy the effect of decreasing CPP due to increasing intracranial pressure (ICP) on cerebral tissue oxygenation was studied.

METHODS

Ten rabbits were subjected to artificially elevated ICP using the cisterna-magna infusion technique. Regional cerebral O(2) saturation of hemoglobin (tiSO(2)), regional tissue concentration of hemoglobin (tiHb), and CPP were recorded continuously. CPP was investigated with respect to tiSO(2). Electrocortical activity was simultaneously recorded by two-channel EEG to determine the onset of ischemia.

RESULTS

Reduced CPP due to increased ICP led to a continuous decrease in tiSO(2.) There was progressive suppression of EEG frequency and amplitude with decreasing CPP in all animals. Onset of EEG-silence due to elevated ICP was observed in a wide range of CPP-values between 9 and 42 mmHg. At the same time tiSO(2) varied merely between 0 and 5%.

CONCLUSIONS

Regarding the EEG effects due to increased ICP (EEG silence), CPP values showed a wide interindividual variability, in contrast to tiSO(2). In our animal model the sole calculation of CPP did not reflect adequate cerebral perfusion.

Comparison of dopamine and norepinephrine after traumatic brain injury and hypoxic-hypotensive insult

After severe brain trauma, blood-brain barrier disruption and alteration of cerebral arteriolar vasoreactive properties may modify the cerebral response to catecholamines. Therefore, the goal of the present study was to compare the effects of dopamine and norepinephrine in a model of brain injury that consisted of a weight-drop model of injury complicated by a 15-min hypoxic-hypotensive insult (HH). Sprague-Dawley rats (n = 7 in each group) received, after brain injury, an infusion of either norepinephrine (TNE group) or dopamine (TDA group) in order to increase cerebral perfusion pressure (CPP) above 70 mm Hg. In addition, a control group (C group, no trauma) and a trauma group (T group, brain injury, no catecholamine infusion) were studied. Mean arterial pressure (MAP), intracranial pressure (ICP, intraparenchymal fiberoptic device), and local cerebral blood flow (LCBF, extradural laser-Doppler fiber) were measured throughout the protocol. In T group, brain injury and HH induced a decrease in CPP (by an increase of ICP and a decrease of MAP), and a decrease of LCBF. Both norepinephrine and dopamine failed to increase CPP, and ICP was significantly higher in TNE and TDA groups than in T group. Interestingly, norepinephrine was not able to alleviate the decrease in MAP. Neither norepinephrine or dopamine could induce an increase of MAP. LCBF decreased similarly in T, TNE and TDA groups. In conclusion, norepinephrine and dopamine are not able to restore values of CPP above 70 mm Hg in a model of severe brain trauma. Furthermore, their systemic vasopressor properties are altered.