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

Analysis of intracranial pressure pulse waveform in studies on cerebrospinal compliance: a narrative review

Continuous monitoring of mean intracranial pressure (ICP) has been an essential part of neurocritical care for more than half a century. Cerebrospinal pressure-volume compensation, i.e. the ability of the cerebrospinal system to buffer changes in volume without substantial increases in ICP, is considered an important factor in preventing adverse effects on the patient's condition that are associated with ICP elevation. However, existing assessment methods are poorly suited to the management of brain injured patients as they require external manipulation of intracranial volume. In the 1980s, studies suggested that spontaneous short-term variations in the ICP signal over a single cardiac cycle, called the ICP pulse waveform, may provide information on cerebrospinal compensatory reserve. In this review we discuss the approaches that have been proposed so far to derive this information, from pulse amplitude estimation and spectral techniques to most recent advances in morphological analysis based on artificial intelligence solutions. Each method is presented with focus on its clinical significance and the potential for application in standard clinical practice. Finally, we highlight the missing links that need to be addressed in future studies in order for ICP pulse waveform analysis to achieve widespread use in the neurocritical care setting.

Assessment of Cerebral Autoregulation Using Invasive and Noninvasive Methods of Intracranial Pressure Monitoring

BACKGROUND

Pulse amplitude index (PAx), a descriptor of cerebrovascular reactivity, correlates the changes of the pulse amplitude of the intracranial pressure (ICP) waveform (AMP) with changes in mean arterial pressure (MAP). AMP relies on cerebrovascular compliance, which is modulated by the state of the cerebrovascular reactivity. PAx can aid in prognostication after acute brain injuries as a tool for the assessment of cerebral autoregulation and could potentially tailor individual management; however, invasive measurements are required for its calculation. Our aim was to evaluate the relationship between noninvasive PAx (nPAx) derived from a novel noninvasive device for ICP monitoring and PAx derived from gold standard invasive methods.

METHODS

We retrospectively analyzed invasive ICP (external ventricular drain) and non-invasive ICP (nICP), via mechanical extensometer (Brain4Care Corp.). Invasive and non-invasive ICP waveform morphology data was collected in adult patients with brain injury with arterial blood pressure monitoring. The time series from all signals were first treated to remove movement artifacts. PAx and nPAx were calculated as the moving correlation coefficients of 10-s averages of AMP or non-invasive AMP (nAMP) and MAP. AMP/nAMP was determined by calculating the fundamental frequency amplitude of the ICP/nICP signal over a 10-s window, updated every 10-s. We then evaluated the relationship between invasive PAx and noninvasive nPAx using the methods of repeated-measures analysis to generate an estimate of the correlation coefficient and its 95% confidence interval (CI). The agreement between the two methods was assessed using the Bland-Altman test.

RESULTS

Twenty-four patients were identified. The median age was 53.5 years (interquartile range 40-70), and intracranial hemorrhage (84%) was the most common etiology. Twenty-one (87.5%) patients underwent mechanical ventilation, and 60% were sedated with a median Glasgow Coma Scale score of 8 (7-15). Mean PAx was 0.0296 ± 0.331, and nPAx was 0.0171 ± 0.332. The correlation between PAx and nPAx was strong (R = 0.70, p < 0.0005, 95% CI 0.687-0.717). Bland-Altman analysis showed excellent agreement, with a bias of - 0.018 (95% CI - 0.026 to - 0.01) and a localized regression trend line that did not deviate from 0.

CONCLUSIONS

PAx can be calculated by conventional and noninvasive ICP monitoring in a statistically significant evaluation with strong agreement. Further study of the applications of this clinical tool is warranted, with the goal of early therapeutic intervention to improve neurologic outcomes following acute brain injuries.

Initial intracranial pressure is an independent predictor of unfavorable functional outcomes after aneurysmal subarachnoid hemorrhage

The authors sought to evaluate whether initial intracranial pressure was associated with functional outcomes following aneurysmal subarachnoid hemorrhage. This retrospective analysis consisted of 54 consecutive patients with aneurysmal subarachnoid hemorrhage and acute symptomatic hydrocephalus requiring emergent placement of an external ventricular drain. Patient demographics, clinical data, intracranial pressure parameters, and radiographic imaging were collected. Functional outcomes were evaluated at 3 months using the modified Rankin Scale and dichotomized as favorable (modified Rankin Scale 0-2) or unfavorable (modified Rankin Scale 3-6). Univariate and multivariate logistic regression analyses were performed to investigate parameters independently associated with functional outcomes. In an adjusted multivariate logistic regression model, initial intracranial pressure (OR: 1.371, 95% CI: 1.119-1.679; p = 0.002) was found to be an independent predictor of unfavorable functional outcomes at 3 months. Receiver operating characteristic curve analysis for the prediction of unfavorable functional outcomes demonstrated that initial intracranial pressure exhibited an acceptable area under the curve (AUC = 0.901, 95% CI: 0.818-0.985; p < 0.001). The optimal predictive threshold to distinguish between favorable and unfavorable functional outcomes was identified at an initial intracranial pressure of 25 mmHg.

Noninvasive detection of elevated ICP using spontaneous tympanic membrane pulsation

Neurological conditions such as traumatic brain injury (TBI) and hydrocephalus may lead to intracranial pressure (ICP) elevation. Current diagnosis methods rely on direct pressure measurement, while CT, MRI and other expensive imaging may be used. However, these invasive or expensive testing methods are often delayed because symptoms of elevated ICP are non-specific. Invasive methods, such as intraventricular catheter, subdural screw, epidural sensor, lumbar puncture, are associated with an increased risk of infection and hemorrhage. On the other hand, noninvasive, low-cost, accurate methods of ICP monitoring can help avoid risks and reduce costs while expediting diagnosis and treatment. The current study proposes and evaluates a novel method for noninvasive ICP monitoring using tympanic membrane pulsation (TMp). These signals are believed to be transmitted from ICP to the auditory system through the cochlear aqueduct. Fifteen healthy subjects were recruited and TMp signals were acquired noninvasively while the subjects performed maneuvers that are known to change ICP. A custom made system utilizing a stethoscope headset and a pressure transducer was used to perform these measurements. Maneuvers included head-up-tilt, head-down-tilt and hyperventilation. When elevated ICP was induced, significant TMp waveform morphological changes were observed in each subject (p < 0.01). These changes include certain waveform slopes and high frequency wave features. The observed changes were reversed by the maneuvers that decreased ICP (p < .01). The study results suggest that TMp waveform measurement and analysis may offer an inexpensive, noninvasive, accurate tool for detection and monitoring of ICP elevations. Further studies are warranted to validate this technique in patients with pathologically elevated ICP.

An update on idiopathic intracranial hypertension in adults: a look at pathophysiology, diagnostic approach and management

Idiopathic intracranial hypertension is a neurological syndrome determined by a rise in intracranial pressure without a detectable cause. Course and prognosis may be changeable, requiring a multidisciplinary approach for its diagnosis and management. Although its precise pathogenesis is still unknown, many studies have been carried out to define the possible causal and associated factors, such as retinoids, steroid hormones, body mass index and recent weight gains, cytokines and adipokines levels. The clinical presentation can be variable including chronic headache, disturbance of vision, diplopia and tinnitus. Even if papilloedema is considered the most specific sign, it could not be observed in more than 5% of patients during the evaluation of the fundus oculi. Neuroradiological signs acquire greater importance in patients who do not present papilloedema and may suggest the diagnosis of idiopathic intracranial hypertension. Other assessments can be useful in the diagnostic process, such as optical coherence tomography, visual evoked potentials, ocular ultrasonography and fundus fluorescein angiography and autofluorescence. Nonetheless, cerebrospinal fluid pressure measurement is required to establish a definite diagnosis. Management may be different, since surgical procedures or lumbar punctures are often required when symptoms develop rapidly leading to a loss of visual function. Apart from these cases, patients can be treated with a pharmacological approach and low-calorie diet, but they also need to be monitored over time since relapses years later are not uncommon.

Intracranial hypertension in patients with aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis

Aneurysmal subarachnoid hemorrhage (aSAH) is a devastating and life-threatening condition with high mortality and morbidity. Even though there is an association with intracranial pressure (ICP) raise and aSAH, there is a lack of recommendations regarding the indications for ICP monitoring in patients with aSAH. Defining what patients are at a higher risk to develop intracranial hypertension and its role in the functional outcome and mortality in patients with aSAH will be the purpose of the following systematic review and meta-analysis. The primary endpoint is to determine the prevalence and impact on mortality of ICP in patients with aSAH. Secondary endpoints aim to describe the variables related to the development of ICP and the relationship between traumatic and aneurysmal etiology of intracranial hypertension. PubMed, Embase, Central Cochrane Registry of Controlled Trials, and research meeting abstracts were searched up to August 2019 for studies that performed ICP monitoring, assessed the prevalence of intracranial hypertension and the mortality, in adults. Newcastle Ottawa scale (NOS) was used to assess study quality. The statistical analysis was performed using the Mantel-Haenszel methodology for the prevalence and mortality of intracranial hypertension for reasons with a randomized effect analysis model. Heterogeneity was assessed by I². A total of 110 bibliographic citations were identified, 20 were considered potentially eligible, and after a review of the full text, 12 studies were considered eligible and 5 met the inclusion criteria for this review. One study obtained 7 points in the NOS, another obtained 6 points, and the rest obtained 5 points. Five studies were chosen for the final analysis, involving 793 patients. The rate of intracranial hypertension secondary to aSAH was 70.69% (95% CI 56.79-82.84%) showing high heterogeneity (I² = 92.48%, p = < 0.0001). The results of the meta-analysis of mortality rate associated with intracranial hypertension after aSAH found a total of four studies, which involved 385 patients. The mortality rate was 30.3% (95% CI: 14.79-48.57%). Heterogeneity was statistically significant (I² = 90.36%; p value for heterogeneity < 0.001). We found that in several studies, they reported that a high degree of clinical severity scale (Hunt and Hess or WNFS) and tomographic (Fisher) were significantly correlated with the increase in ICP above 20 mmHg (P < 0.05). The interpretation of the results could be underestimated for the design heterogeneity of the included studies. New protocols establishing the indications for ICP monitoring in aSAH are needed. Given the high heterogeneity of the studies included, we cannot provide clinical recommendations regarding this issue.

From paradigm to paradox: divergency between intracranial pressure and intracranial pulse pressure during atmospheric pressure fall: a case study

BACKGROUND

The main objectives are to determine relation between intracranial pressure and its amplitude and to ascertain meteorological variables as possible confounding factors. This is a retrospective observational study of a patient with suspicion of normotensive hydrocephalus.

METHODS

The intracranial pressure, the blood pressure, atmospheric pressure and geomagnetic activity were continuously monitored capturing extraordinary sudden and unexpected atmospheric pressure fall. The physiological changes exceptionally observed during suddenweather changes were described by means of statistical parameters. The data from 73 consecutive hourly measurements was eligible for this analysis. It contained 1022 data points corresponding to all recorded parameters, both climate and physiological ones.

RESULTS

After initial stable period, the atmospheric pressure started to decrease from 767 mmHg to 746 mmHg. In parallel, the mean intracranial pressure increased significantly from 4 mmHg to 14 mmHg. Thus, the mean intracranial pressure changed inversely during atmospheric pressure drop. Whereas mean intracranial pressure increased by 10 mmHg during atmospheric pressure fall, the intracranial amplitude decreased by 5 mmHg. On timescale of several dozen hours in this study, the short-term periodic diurnal variations of intracranial pressure and blood pressure were displayed. The association between diurnal atmospheric pressure oscillation and geomagnetic activity variation was observed. Both intracranial and blood pressure variations differed significantly between day and night.

CONCLUSIONS

This study shows that increasing intracranial pressure is associated with its paradoxically decreasing amplitude under the influence of sudden and unexpected barometric pressure fall. This study suggests that abrupt changes in atmospheric pressure might impact intracranial pressure.

The best marker for guiding the clinical management of patients with raised intracranial pressure-the RAP index or the mean pulse amplitude?

Raised intracranial pressure is a common problem in a variety of neurosurgical conditions including traumatic brain injury, hydrocephalus and intracranial haemorrhage. The clinical management of these patients is guided by a variety of haemodynamic, biochemical and clinical factors. However to date there is no single parameter that is used to guide clinical management of patients with raised intracranial pressure (ICP). However, the role of ICP indices, specifically the mean pulse amplitude (AMP) and RAP index [correlation coefficient (R) between AMP amplitude (A) and mean ICP pressure (P); index of compensatory reserve], as an indicator of true ICP has been investigated. Whilst the RAP index has been used both as a descriptor of neurological deterioration in TBI patients and as a way of characterising the compensatory reserve in hydrocephalus, more recent studies have highlighted the limitation of the RAP index due to the influence that baseline effect errors have on the mean ICP, which is used in the calculation of the RAP index. These studies have suggested that the ICP mean pulse amplitude may be a more accurate marker of true intracranial pressure due to the fact that it is uninfluenced by the mean ICP and, therefore, the AMP may be a more reliable marker than the RAP index for guiding the clinical management of patients with raised ICP. Although further investigation needs to be undertaken in order to fully assess the role of ICP indices in guiding the clinical management of patients with raised ICP, the studies undertaken to date provide an insight into the potential role of ICP indices to treat raised ICP proactively rather than reactively and therefore help prevent or minimise secondary brain injury.

Intracranial Pressure Assessment in Traumatic Head Injury with Hemorrhage Via Optic Nerve Sheath Diameter

Our purpose was to improve the technique of measuring optic nerve sheath diameter (ONSD) for intracranial pressure (ICP) monitoring in cases of traumatic head injury with hemorrhage. In a retrospective study, computed tomography (CT) data of 312 adult patients were collected and analyzed. ONSDs were measured at 3 mm and 8-10 mm distance from the globe together with the eyeball transverse diameter (ETD). The ONSD/ETD ratio was calculated. The correlation analysis was performed with gender, age, Glasgow Coma Scale score, and Glasgow Outcome Score. ONSD was enlarged in all cases when CT scans indicated hematoma. Enlarged right/left ONSDs were 6.5 ± 1.5/6.4 ± 1.3 mm at 3 mm and 6.6 ± 0.8/6.6 ± 0.6 mm at 8-10 mm from the globe (cut-off value > 5.5 mm). ONSD/ETD ratio was 0.29 ± 0.05, compared with 0.19 ± 0.02 in healthy adults (p < 0.01). We did not find a correlation between ONSD/ETD ratio and initial Glasgow Coma Scale score, but there was an inverse correlation between ONSD/ETD ratio and Glasgow Outcome Score (r = -0.83). We conclude that in cases with a traumatic head injury with hemorrhage, the ONSD is significantly enlarged, indicating elevated ICP. In ICP assessment, the most accurate results can be obtained if the ONSD is measured 8-10 mm from the globe and the ONSD/ETD ratio is calculated.

Multimodal MRI characterization of experimental subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is associated with significant morbidity and mortality. We implemented an in-scanner rat model of mild SAH in which blood or vehicle was injected into the cistern magna, and applied multimodal MRI to study the brain prior to, immediately after (5min to 4h), and upto 7days after SAH. Vehicle injection did not change arterial lumen diameter, apparent diffusion coefficient (ADC), T2, venous signal, vascular reactivity to hypercapnia, or foot-fault scores, but mildly reduce cerebral blood flow (CBF) up to 4h, and open-field activity up to 7days post injection. By contrast, blood injection caused: (i) vasospasm 30min after SAH but not thereafter, (ii) venous abnormalities at 3h and 2days, delayed relative to vasospasm, (iii) reduced basal CBF and to hypercapnia 1-4h but not thereafter, (iv) reduced ADC immediately after SAH but no ADC and T2 changes on days 2 and 7, and (v) reduced open-field activities in both SAH and vehicle animals, but no significant differences in open-field activities and foot-fault tests between groups. Mild SAH exhibited transient and mild hemodynamic disturbances and diffusion changes, but did not show apparent ischemic brain injury nor functional deficits.

Relationship between intracranial pressure and aneurysmal subarachnoid hemorrhage grades

OBJECTIVE

Intracranial pressure (ICP) is frequently elevated following aneurysmal subarachnoid hemorrhage (aSAH). In this prospective study, the factors associated with increased ICP and the relationship between ICP and the aSAH grade were evaluated.

METHODS

Consecutive patients with prospective aSAH were enrolled within 24h after disease onset. Clinical scoring, including the Hunt and Hess scale, the WFNS scale and the Fisher scale, was performed upon admission. Consciousness was evaluated based on the Glasgow Coma Scale, and the subarachnoid hemorrhage volume was determined according to a CT scan. Then, an ICP monitor was placed, and ICP was recorded. The relationship between ICP and the aSAH grade was examined using Spearman correlation coefficients. Additionally, some clinical characteristics of the patients, including age, sex, location and size of the aneurysm, hydrocephalus and rebleeding, were recorded and analyzed.

RESULTS

A total of 165 patients were enrolled in this study. Of these patients, 111 (67.2%) displayed elevated ICP (≥ 20 mm Hg). The patients who underwent intubation or who experienced rebleeding or hydrocephalus displayed an elevated ICP compared with those who did not (P = 0.002, P = 0.001 and P = 0.008, respectively). There was a positive linear correlation between ICP and both the Hunt and Hess grade and the WFNS grade (correlation coefficients of 0.731 and 0.761, respectively). The correlation between ICP and the Fisher grade was weak according to the correlation coefficient of only 0.093.

CONCLUSION

ICP following aSAH positively correlates with the patient's consciousness, but no relationship was detected between ICP and the subarachnoid hemorrhage volume.

Are intracranial pressure wave amplitudes measurable through lumbar puncture?

OBJECTIVE

The aim of this study was to investigate whether pulsations measured in the brain correspond to those measured in lumbar space, and subsequently whether lumbar punctures could replace invasive recordings.

METHODS

In ten patients with normal pressure hydrocephalus, simultaneous recordings of the intracranial pressure (ICP; intraparenchymal) and lumbar pressure (LP; cerebrospinal fluid pressure) were performed. During registration, pressure was altered between resting pressure and 45 mmHg using an infusion test. Data were analyzed regarding pulsations (i.e., amplitudes). Also, the pressure sensors were compared in a bench test.

RESULTS

The correlation between intracranial and lumbar amplitudes was 0.98. At resting pressure, and moderately elevated ICP, intracranial pulse amplitudes exceeded that of lumbar space with about 0.9 mmHg. At the highest ICP, the difference changed to -0.2 mmHg. The bench test showed that the agreement of sensor readings was good at resting pressure, but reduced at higher amplitudes.

CONCLUSIONS

Compared to intracranial registrations, amplitudes measured through lumbar puncture were slightly attenuated. The bench test showed that differences were not attributable to dissimilarities of the sensor systems. A lumbar pressure amplitude measurement is an alternative to ICP recording, but the thresholds for what should be interpreted as elevated amplitudes need to be adjusted.

Semi-supervised detection of intracranial pressure alarms using waveform dynamics

Patient monitoring systems in intensive care units (ICU) are usually set to trigger alarms when abnormal values are detected. Alarms are generated by threshold-crossing rules that lead to high false alarm rates. This is a recognized issue that causes alarm fatigue, waste of human resources, and increased patient risks. Recently developed smart alarm models require alarms to be validated by experts during the training phase. The manual annotation process involved is time-consuming and virtually impossible to achieve for the thousands of alarms recorded in the ICU every week. To tackle this problem, we investigate in this study if the use of semi-supervised learning methods, that can naturally integrate unlabeled data samples in the model, can be used to improve the accuracy of the alarm detection. As a proof of concept, the detection system is evaluated on intracranial pressure (ICP) signal alarms. Specific morphological and trending features are extracted from the ICP signal waveform to capture the dynamic of the signal prior to alarms. This study is based on a comprehensive dataset of 4791 manually labeled alarms recorded from 108 neurosurgical patients. A comparative analysis is provided between kernel spectral regression (SR-KDA) and support vector machine (SVM) both modified for the semi-supervised setting. Results obtained during the experimental evaluations indicate that the two models can significantly reduce false alarms using unlabeled samples; especially in the presence of a restrained number of labeled examples. At a true alarm recognition rate of 99%, the false alarm reduction rates improved from 9% (supervised) to 27% (semi-supervised) for SR-KDA, and from 3% (supervised) to 16% (semi-supervised) for SVM.

Continuous monitoring of cerebrovascular reactivity using pulse waveform of intracranial pressure

BACKGROUND

Guidelines for the management of traumatic brain injury (TBI) call for the development of accurate methods for assessment of the relationship between cerebral perfusion pressure (CPP) and cerebral autoregulation and to determine the influence of quantitative indices of pressure autoregulation on outcome. We investigated the relationship between slow fluctuations of arterial blood pressure (ABP) and intracranial pressure (ICP) pulse amplitude (an index called PAx) using a moving correlation technique to reflect the state of cerebral vasoreactivity and compared it to the index of pressure reactivity (PRx) as a moving correlation coefficient between averaged values of ABP and ICP.

METHODS

A retrospective analysis of prospective 327 TBI patients (admitted on neurocritical care unit of a university hospital in the period 2003-2009) with continuous ABP and ICP monitoring.

RESULTS

PAx was worse in patients who died compared to those who survived (-0.04 ± 0.15 vs. -0.16 ± 0.15, χ2 = 28, p < 0.001). In contrast to PRx, PAx was able to differentiate between fatal and non-fatal outcome in a group of 120 patients with ICP levels below 15 mmHg (-0.04 ± 0.16 vs. -0.14 ± 0.16, χ2 = 6, p = 0.01).

CONCLUSIONS

PAx is a new modified index of cerebrovascular reactivity which performs equally well as established PRx in long-term monitoring in severe TBI patients, but importantly is potentially more robust at lower values of ICP. In view of establishing an autoregulation-oriented CPP therapy, continuous determination of PAx is feasible but its value has to be evaluated in a prospective controlled trail.

A randomized and blinded single-center trial comparing the effect of intracranial pressure and intracranial pressure wave amplitude-guided intensive care management on early clinical state and 12-month outcome in patients with aneurysmal subarachnoid hemorrhage

BACKGROUND

In patients with aneurysmal subarachnoid hemorrhage (SAH), preliminary results indicate that the amplitude of the single intracranial pressure (ICP) wave is a better predictor of the early clinical state and 6-month outcome than the mean ICP.

OBJECTIVE

To perform a randomized and blinded single-center trial comparing the effect of mean ICP vs mean ICP wave amplitude (MWA)-guided intensive care management on early clinical state and outcome in patients with aneurysmal SAH.

METHODS

Patients were randomized to 2 different types of ICP management: maintenance of mean ICP less than 20 mm Hg and MWA less than 5 mm Hg. Early clinical state was assessed daily using the Glasgow Coma Scale. The primary efficacy variable was 12-month outcome in terms of the Rankin Stroke Score.

RESULTS

Ninety-seven patients were included in the study. There were no significant differences in treatment between the 2 groups apart from a larger volume of cerebrospinal fluid drained during week 1 in the MWA group. There was a tendency toward higher Glasgow Coma Scale scores in the MWA group during weeks 1 (P = .08) and 2 (P = .07). Outcome in terms of Rankin Stroke Score at 12 months was significantly better in the MWA group (P < .05).

CONCLUSION

This randomized and blinded trial disclosed a significant better primary efficacy variable (Rankin Stroke Score after 12 months) in the MWA patient group. We suggest that proactive intensive care management with MWA-tailored cerebrospinal fluid drainage during the first week improves aneurysmal SAH outcome.

Pulsatile intracranial pressure and cerebral autoregulation after traumatic brain injury

BACKGROUND

Strong correlation between mean intracranial pressure (ICP) and its pulse wave amplitude (AMP) has been demonstrated in different clinical scenarios. We investigated the relationship between invasive mean arterial blood pressure (ABP) and AMP to explore its potential role as a descriptor of cerebrovascular pressure reactivity after traumatic brain injury (TBI).

METHODS

We retrospectively analyzed data of patients suffering from TBI with brain monitoring. Transcranial Doppler blood flow velocity, ABP, ICP were recorded digitally. Cerebral perfusion pressure (CPP) and AMP were derived. A new index-pressure-amplitude index (PAx)-was calculated as the Pearson correlation between (averaged over 10 s intervals) ABP and AMP with a 5 min long moving average window. The previously introduced transcranial Doppler-based autoregulation index Mx was evaluated in a similar way, as the moving correlation between blood flow velocity and CPP. The clinical outcome was assessed after 6 months using the Glasgow outcome score.

RESULTS

293 patients were studied. The mean PAx was -0.09 (standard deviation 0.21). This negative value indicates that, on average, an increase in ABP causes a decrease in AMP and vice versa. PAx correlated strong with Mx (R (2) = 0.46, P < 0.0002). PAx also correlated with age (R (2) = 0.18, P < 0.05). PAx was found to have as good predictive outcome value (area under curve 0.71, P < 0.001) as Mx (area under curve 0.69, P < 0.001).

CONCLUSIONS

We demonstrated significant correlation between the known cerebral autoregulation index Mx and PAx. This new index of cerebrovascular pressure reactivity using ICP pulse wave information showed to have a strong association with outcome in TBI patients.

The pulsating brain: A review of experimental and clinical studies of intracranial pulsatility

The maintenance of adequate blood flow to the brain is critical for normal brain function; cerebral blood flow, its regulation and the effect of alteration in this flow with disease have been studied extensively and are very well understood. This flow is not steady, however; the systolic increase in blood pressure over the cardiac cycle causes regular variations in blood flow into and throughout the brain that are synchronous with the heart beat. Because the brain is contained within the fixed skull, these pulsations in flow and pressure are in turn transferred into brain tissue and all of the fluids contained therein including cerebrospinal fluid. While intracranial pulsatility has not been a primary focus of the clinical community, considerable data have accrued over the last sixty years and new applications are emerging to this day. Investigators have found it a useful marker in certain diseases, particularly in hydrocephalus and traumatic brain injury where large changes in intracranial pressure and in the biomechanical properties of the brain can lead to significant changes in pressure and flow pulsatility. In this work, we review the history of intracranial pulsatility beginning with its discovery and early characterization, consider the specific technologies such as transcranial Doppler and phase contrast MRI used to assess various aspects of brain pulsations, and examine the experimental and clinical studies which have used pulsatility to better understand brain function in health and with disease.

Static and pulsatile intracranial pressure in idiopathic intracranial hypertension

OBJECTIVE

The aim of this observational study was to characterize the static and pulsatile intracranial pressure (ICP) in conservatively (medically) treated idiopathic intracranial hypertension (IIH) patients in need of shunt surgery, and also in patients with chronic daily headache (CDH) without visual disturbances.

METHODS

The material includes 14 IIH patients and 7 CDH patients in whom ICP was monitored continuously over-night. Static ICP was characterized by mean ICP, pulsatile ICP was characterized by the wave amplitude, rise time, and rise time coefficient.

RESULTS

In the IIH group all 14 had headache and visual disturbances. Mean ICP was high (> 15 mmHg) in only 7 patients (50%), while mean ICP wave amplitude was high (≥ 4 mmHg) in all 14 (100%). All IIH patients were shunted and improved clinically thereafter (i.e., relief from visual disturbances and/or headache). None in the CDH group had high mean ICP or mean ICP wave amplitude, and none were shunted.

CONCLUSIONS

In this cohort of 14 conservatively treated IIH patients with lasting and shunt-responsive headache and visual disturbances, the mean ICP wave amplitude was elevated (≥ 4 mmHg) in all patients despite normal mean ICP (< 15 mmHg) in 7 patients (all but one on medication). Therefore, the pulsatile ICP may be more relevant than the static ICP in the diagnostic setting for patients with IIH. Further prospective standardized approaches are warranted.

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.

Intracranial pressure pulse amplitude during changes in head elevation: a new parameter for determining optimum cerebral perfusion pressure?

OBJECTIVE

During short-term postural changes, the factors determining the amplitude of intracranial pulse pressure (ICPPA) remain constant, except for cerebrovascular resistance (CVR). Therefore, it may be possible to draw conclusions from the ICPPA onto the cerebrovascular resistance (CVR) and thus the relative change in cerebral perfusion pressure (CPP).

METHODS

Age, sex, disease, Glasgow Coma Scale score, placement of ventricular drain, blood gas analysis, and parameters of airway management were prospectively recorded in 40 patients. The changes in intracranial pressure (ICP), CPP, mean arterial pressure (MAP), and ICPPA at head elevations of 0 degrees, 30 degrees, and 60 degrees were measured and analyzed online. Status of cerebrovascular autoregulation was checked using the pressure-reactivity index (PRx).

RESULTS

Altogether 36 subjects fulfilled the study conditions. Three patients had positive PRx indicating disturbed autoregulation and were excluded. Thus, 33 were left for analysis (18 females and 15 males). All of them were sedated and mechanically ventilated with Glasgow Coma scores ranging from 3-8. During change in head elevation from 0 degrees to 60 degrees, we found a significant (p < 0.05) improvement of the ICP, an increase of the ICCPA, a reduction of the MAP, and a decrease in the CPP. Increasing ICPPA was linked to decreasing CPP (0 degrees to 60 degrees, r = -0.42, p < 0.05).

CONCLUSIONS

Head elevation is an important part of the ICP and CPP therapy in neurointensive care. When searching for the patient-specific optimum upper body position, ICPPA may provide additional information. Providing that the cerebral autoregulation is intact, the lowest ICPPA of a patient corresponds to the individual upper body position with the highest CPP.

Predictors of 1-year outcome after coiling for poor-grade subarachnoid aneurysmal hemorrhage

OBJECTIVE

To describe features in patients admitted to the intensive care unit (ICU) for poor-grade aneurysmal subarachnoid hemorrhage (SAH) and to identify predictors of 12-month outcome.

METHODS

We conducted a controlled observational study of 51 consecutive patients treated with endovascular coiling within 96 h of rupture for poor-grade aneurysmal SAH (20 men and 31 women, age 54 +/- 12 years). We recorded co-morbidities; initial severity; aneurysm location; occurrence of acute hydrocephalus, initial seizures, and/or neurogenic lung edema; troponin values, Fisher grade; computed tomography (CT) findings; treatment intensity; and occurrence of vasospasm. The brain injury marker S100B was assayed daily over the first 8 days. Glasgow Outcome Scores (GOS) were recorded at ICU discharge, at 6 and 12 months. The main outcome criterion was the 1-year GOS score, which we used to classify patients as having a poor outcome (GOS 1-3) or a good outcome (GOS 4-5).

RESULTS

Overall, clinical status after 1 year was very good (GOS 5) in 41% of patients and good (GOS 4) in 16%. Neither baseline characteristics nor interventions differed significantly between patients with good outcome (GOS 4-5) and those with poor outcome (GOS 1-3). Persistent intracranial pressure elevation and higher mean 8-day S100B value significantly and independently predicted the 1-year GOS outcome (P = 0.008 and P = 0.001, respectively).

CONCLUSIONS

Patients in poor clinical condition after SAH have more than a 50:50 chance of a favorable outcome after 1 year. High mean 8-day S100B value and persistent intracranial hypertension predict a poor outcome (GOS 1-3) after 1 year.

Association between intracranial pulse pressure levels and brain energy metabolism in a patient with an aneurysmal subarachnoid haemorrhage

This report addresses whether intracranial pulse pressure amplitudes are associated with brain energy metabolism, examined by intracerebral microdialysis. We present a 65-year-old female with an aneurysmal subarachnoid haemorrhage (SAH) from a left posterior communicating artery (PCOM) aneurysm. She underwent simultaneous intracranial pressure (ICP) monitoring and microdialysis (MD) as part of a diagnostic workout because of a lack of clinical improvement after long-term intensive care management. Over a 4-day period, a total of 128 samples of metabolites (glutamate, glycerol, lactate and pyruvate) were gathered, allowing retrospective comparisons with the levels of intracranial pulse pressure amplitudes (the mean ICP wave amplitude). During this 4-day period, mean ICP was normal (<15 mmHg), while mean ICP wave amplitude was high (>/=5 mmHg) in 47% of the recording time. There was a highly significant relationship between the levels of the mean ICP wave amplitude and the levels of glutamate, glycerol and lactate/pyruvate ratio. The levels of metabolites were increased when the mean ICP wave amplitude was >/=5 mmHg as compared with mean ICP wave amplitude levels <5 mmHg. We tentatively suggest that increased mean ICP wave amplitudes indicative of reduced intracranial compliance can be associated with brain ischaemia.

The frequency domain versus time domain methods for processing of intracranial pressure (ICP) signals

Two methods for analyzing intracranial pressure (ICP) waveforms were compared. The frequency domain (FD) method converts the signal from the time domain to the frequency domain by a fast Fourier transform (FFT), while the time domain (TD) method calculates peak-to-peak value of the pulse waveform directly from the time samples. First, the ICP signal was regenerated from the first harmonic of the FFT and compared against the time domain raw ICP signal. We found that the FD method may underestimate pulse amplitude if there is heart rate variability or a high harmonic distortion. Second, to explore the significance in a larger data set, differences between FD- and TD-derived pulse amplitudes were determined for a total of 50,978 6-s time windows of 79 head injury patients. The mean difference in pulse pressure amplitude was 2.9 mmHg for the 50,978 6-s time windows. Differences between TD- and FD-derived pulse amplitudes were >or= 2.0 mmHg in 58.8% of the 50,978 time windows. In about 33% of time windows FD amplitudes were <2 mmHg when TD amplitudes were >or= 4 mmHg, and vice versa. Hence, the TD method is superior to the FD method for calculation of pulse amplitudes. Nevertheless, in this material both the TD and FD methods revealed significantly elevated pulse amplitudes in head injury patients with bad outcome (i.e. Glasgow Outcome Score 1-3).

From intracranial pressure to intracranial pressure wave-guided intensive care management of a patient with an aneurysmal subarachnoid haemorrhage

We report on a 65-year-old female with an aneurysmal subarachnoid hemorrhage (SAH) that was followed clinically, radiologically and electrophysiologically before and after converting from intracranial pressure (ICP)-guided to ICP wave-guided intensive care management. Intracranial pressure-guided management is aimed at keeping mean ICP < 15-20 mmHg, while ICP wave-guided management is aimed at keeping mean ICP wave amplitude < 5 mmHg. The aims of management were obtained by adjusting cerebrospinal fluid (CSF) draining volume from her external ventricular drain. No improvement was seen clinically or in cerebral magnetic resonance imaging (MRI) scans during the ICP-guided management. Clinical, MRI and neurophysiologic (electroencephalography and auditory evoked responses) improvements were obvious within 2 days after converting from ICP- to ICP wave-guided management. This case report describes how we used various ICP parameters to guide intensive care management of an aneurysmal SAH patient.