In vivo accuracy of two intraparenchymal intracranial pressure monitors

Ventriculostomy Associated with Reduced Mortality in Severe Traumatic Brain Injury Compared to Parenchymal ICP Monitoring: A Propensity Score-Adjusted Analysis

BACKGROUND

There is a lack of data on whether intracranial pressure (ICP)-guided therapy with an intraparenchymal fiberoptic monitor (IPM) or an external ventricular drain (EVD) leads to superior outcomes. Our goal is to determine the relationship between ICP-guided therapy with an EVD or IPM and mortality.

METHODS

Retrospective analysis of severe traumatic brain injury cases that required IPM or EVD placement for ICP-guided therapy from January 1, 2010 to December 31, 2020. The data were obtained from the Pennsylvania Trauma Systems Foundation registry.

RESULTS

A total of 2305 patients met the inclusion criteria, with 1048 (45.5%) IPM and 1257 (54.5%) EVD placed. Inpatient mortality occurred in 337 (32.2%) and 334 (26.6%) patients in the IPM and EVD cohorts, respectively (P = 0.003). Even among those treated medically only, inpatient mortality occurred in 171 (30.8%) of those with an IPM and in 100 (23.4%) of those with an EVD (P = 0.010). Multivariable logistic regression analysis showed that older age (odds ratio [OR] 1.03, P < 0.001), lower Glasgow Coma Scale (GCS) score (OR 1.16, P < 0.001), requiring surgery (OR 1.22, P = 0.049), and an IPM (OR 1.40, P = 0.001) were significant predictors of mortality. Propensity score-adjusted analysis using inverse probability of treatment weighted method revealed a 28% decrease in mortality and a 14% decrease in length of hospital stay with EVD use when adjusting for age, sex, GCS, Injury Severity Score, surgery, and Hispanic ethnicity.

CONCLUSIONS

A significant mortality benefit was associated with the use of EVD compared to IPM. This mortality benefit was observed regardless of whether patients required surgery or not.

Physiological Monitoring in Patients with Acute Brain Injury: A Multimodal Approach

Neurocritical care management of acute brain injury (ABI) is focused on identification, prevention, and management of secondary brain injury (SBI). Physiologic monitoring of the brain and other organ systems has a role to predict patient recovery or deterioration, guide individualized therapeutic interventions, and measure response to treatment, with the goal of improving patient outcomes. In this review, we detail how specific physiologic markers of brain injury and neuromonitoring tools are integrated and used in ABI patients to develop therapeutic approaches to prevent SBI.

Interactions of brain, blood, and CSF: a novel mathematical model of cerebral edema

Background

Previous models of intracranial pressure (ICP) dynamics have not included flow of cerebral interstitial fluid (ISF) and changes in resistance to its flow when brain swelling occurs. We sought to develop a mathematical model that incorporates resistance to the bulk flow of cerebral ISF to better simulate the physiological changes that occur in pathologies in which brain swelling predominates and to assess the model’s ability to depict changes in cerebral physiology associated with cerebral edema.

Methods

We developed a lumped parameter model which includes a representation of cerebral ISF flow within brain tissue and its interactions with CSF flow and cerebral blood flow (CBF). The model is based on an electrical analog circuit with four intracranial compartments: the (1) subarachnoid space, (2) brain, (3) ventricles, (4) cerebral vasculature and the extracranial spinal thecal sac. We determined changes in pressure and volume within cerebral compartments at steady-state and simulated physiological perturbations including rapid injection of fluid into the intracranial space, hyperventilation, and hypoventilation. We simulated changes in resistance to flow or absorption of CSF and cerebral ISF to model hydrocephalus, cerebral edema, and to simulate disruption of the blood–brain barrier (BBB).

Results

The model accurately replicates well-accepted features of intracranial physiology including the exponential-like pressure–volume curve with rapid fluid injection, increased ICP pulse pressure with rising ICP, hydrocephalus resulting from increased resistance to CSF outflow, and changes associated with hyperventilation and hypoventilation. Importantly, modeling cerebral edema with increased resistance to cerebral ISF flow mimics key features of brain swelling including elevated ICP, increased brain volume, markedly reduced ventricular volume, and a contracted subarachnoid space. Similarly, a decreased resistance to flow of fluid across the BBB leads to an exponential-like rise in ICP and ventricular collapse.

Conclusions

The model accurately depicts the complex interactions that occur between pressure, volume, and resistances to flow in the different intracranial compartments under specific pathophysiological conditions. In modelling resistance to bulk flow of cerebral ISF, it may serve as a platform for improved modelling of cerebral edema and blood–brain barrier disruption that occur following brain injury.

Intracranial and Cerebral Perfusion Pressure Thresholds Associated With Inhospital Mortality Across Pediatric Neurocritical Care

OBJECTIVES

Targets for treatment of raised intracranial pressure or decreased cerebral perfusion pressure in pediatric neurocritical care are not well defined. Current pediatric guidelines, based on traumatic brain injury, suggest an intracranial pressure target of less than 20 mm Hg and cerebral perfusion pressure minimum of 40-50 mm Hg, with possible age dependence of cerebral perfusion pressure. We sought to define intracranial pressure and cerebral perfusion pressure thresholds associated with inhospital mortality across a large single-center pediatric neurocritical care cohort.

DESIGN

Retrospective chart review.

SETTING

PICU, single quaternary-care center.

PATIENTS

Individuals receiving intracranial pressure monitoring from January 2012 to December 2016.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Intracranial pressure and cerebral perfusion pressure measurements from 262 neurocritical care patients (87 traumatic brain injury and 175 nontraumatic brain injury; 63% male; 8.3 ± 5.8 yr; mortality 11.1%). Mean intracranial pressure and cerebral perfusion pressure had area under the receiver operating characteristic curves of 0.75 and 0.64, respectively, for association of inhospital mortality. Cerebral perfusion pressure cut points increased with age (< 2 yr = 47, 2 to < 8 yr = 58 mm Hg, ≥ 8 yr = 73 mm Hg). In the traumatic brain injury subset, mean intracranial pressure and cerebral perfusion pressure had area under the receiver operating characteristic curves of 0.70 and 0.78, respectively, for association of inhospital mortality. Traumatic brain injury cerebral perfusion pressure cut points increased with age (< 2 yr = 45, 2 to < 8 yr = 57, ≥ 8 yr = 68 mm Hg). Mean intracranial pressure greater than 15 mm Hg, male sex, and traumatic brain injury status were independently associated with inhospital mortality (odds ratio, 14.23 [5.55-36.46], 2.77 [1.04-7.39], and 2.57 [1.03-6.38], respectively; all p < 0.05). Mean cerebral perfusion pressure less than 67 mm Hg and traumatic brain injury status were independently associated with inhospital mortality (odds ratio, 5.16 [2.05-12.98] and 3.71 [1.55-8.91], respectively; both p < 0.01). In the nontraumatic brain injury subset, mean intracranial pressure had an area under the receiver operating characteristic curve 0.77 with an intracranial pressure cut point of 15 mm Hg, whereas mean cerebral perfusion pressure was not predictive of inhospital mortality.

CONCLUSIONS

We identified mean intracranial pressure thresholds, utilizing receiver operating characteristic and regression analyses, associated with inhospital mortality that is below current guidelines-based treatment targets in both traumatic brain injury and nontraumatic brain injury patients, and age-dependent cerebral perfusion pressure thresholds associated with inhospital mortality that were above current guidelines-based targets in traumatic brain injury patients. Further study is warranted to identify data-driven intracranial pressure and cerebral perfusion pressure targets in children undergoing intracranial pressure monitoring, whether for traumatic brain injury or other indications.

Long-duration spaceflight alters estimated intracranial pressure and cerebral blood velocity

Key points

During long‐duration spaceflights, some astronauts develop structural ocular changes including optic disc oedema that resemble signs of intracranial hypertension.

In the present study, intracranial pressure was estimated non‐invasively (nICP) using a model‐based analysis of cerebral blood velocity and arterial blood pressure waveforms in 11 astronauts before and after long‐duration spaceflights.

Our results show that group‐averaged estimates of nICP decreased significantly in nine astronauts without optic disc oedema, suggesting that the cephalad fluid shift during long‐duration spaceflight rarely increased postflight intracranial pressure.

The results of the two astronauts with optic disc oedema suggest that both increases and decreases in nICP are observed post‐flight in astronauts with ocular alterations, arguing against a primary causal relationship between elevated ICP and spaceflight associated optical changes.

Cerebral blood velocity increased independently of nICP and spaceflight‐associated ocular alterations. This increase may be caused by the reduced haemoglobin concentration after long‐duration spaceflight.

Abstract

Persistently elevated intracranial pressure (ICP) above upright values is a suspected cause of optic disc oedema in astronauts. However, no systematic studies have evaluated changes in ICP from preflight. Therefore, ICP was estimated non‐invasively before and after spaceflight to test whether ICP would increase after long‐duration spaceflight. Cerebral blood velocity in the middle cerebral artery (MCAv) was obtained by transcranial Doppler sonography and arterial pressure in the radial artery was obtained by tonometry, in the supine and sitting positions before and after 4−12 months of spaceflight in 11 astronauts (10 males and 1 female, 46 ± 7 years old at launch). Non‐invasive ICP (nICP) was computed using a validated model‐based estimation method. Mean MCAv increased significantly after spaceflight (ANOVA, P = 0.007). Haemoglobin decreased significantly after spaceflight (14.6 ± 0.8 to 13.3 ± 0.7 g/dL, P < 0.001). A repeated measures correlation analysis indicated a negative correlation between haemoglobin and mean MCAv (r = −0.589, regression coefficient = −4.68). The nICP did not change significantly after spaceflight in the 11 astronauts. However, nICP decreased significantly by 15% in nine astronauts without optic disc oedema (P < 0.005). Only one astronaut increased nICP to relatively high levels after spaceflight. Contrary to our hypothesis, nICP did not increase after long‐duration spaceflight in the vast majority (>90%) of astronauts, suggesting that the cephalad fluid shift during spaceflight does not systematically or consistently elevate postflight ICP in astronauts. Independently of nICP and ocular alterations, the present results of mean MCAv suggest that long‐duration spaceflight may increase cerebral blood flow, possibly due to reduced haemoglobin concentration.

During long‐duration spaceflights, some astronauts develop structural ocular changes including optic disc oedema that resemble signs of intracranial hypertension.

In the present study, intracranial pressure was estimated non‐invasively (nICP) using a model‐based analysis of cerebral blood velocity and arterial blood pressure waveforms in 11 astronauts before and after long‐duration spaceflights.

Our results show that group‐averaged estimates of nICP decreased significantly in nine astronauts without optic disc oedema, suggesting that the cephalad fluid shift during long‐duration spaceflight rarely increased postflight intracranial pressure.

The results of the two astronauts with optic disc oedema suggest that both increases and decreases in nICP are observed post‐flight in astronauts with ocular alterations, arguing against a primary causal relationship between elevated ICP and spaceflight associated optical changes.

Cerebral blood velocity increased independently of nICP and spaceflight‐associated ocular alterations. This increase may be caused by the reduced haemoglobin concentration after long‐duration spaceflight.

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.

Pulsatility Index Reflects Intracranial Pressure Better than Resistive Index in Patients with Clinical Features of Intracranial Hypertension

Background  The intracranial pressure (ICP) is measured through various noninvasive methods to overcome complications of invasive ICP monitoring. In this study, transcranial Doppler was used to measure pulsatility index (PI) and resistive index (RI) that were correlated with opening intraventricular ICP. The opening intraventricular ICP was measured with the placement of intraventricular catheter in lateral ventricle without loss of cerebrospinal fluid. Methods  The prospective, observational study was conducted on 40 patients with clinical and radiological features of raised ICP who underwent either endoscopic third ventriculostomy or ventriculoperitoneal shunt surgery. The PI and RI were measured simultaneously with opening ICP measurements under general anesthesia. Both PI and RI were correlated with ICP by using Pearson correlation coefficient. The receiver operating characteristic (ROC) curve was used to get the optimal values of PI ad RI for corresponding ICP values. Results  The mean PI was 1.01 ± 0.41 and mean RI was 0.59 ± 0.32. The mean opening ICP value was 21.81 ± 8.68 mm Hg. The correlation between PI and RI with ICP was a statistically significant with correlation coefficient of 0.697 and 0.503, respectively. The ROC curve shown statistically significant association between PI and ICP from 15 to 40 mm Hg, whereas the association between RI and ICP was from 15 to 25 mm Hg, with various sensitivity and specificity. Conclusion  The opening intraventricular ICP correlated better with PI than RI in patients with features of raised ICP.

A Frequency-domain Approach to Noninvasive Intracranial Pressure Estimation

Intracranial pressure (ICP) is a cranial vital sign, crucial in the monitoring and treatment of several neurological injuries. The clinically accepted measurement modalities of ICP are highly invasive, carrying risks of infection and limiting the benefits of ICP measurement to a small subset of critically ill patients. This work aims to take a step towards developing an accurate noninvasive means of estimating ICP, by utilizing a model-based frequency-domain approach. The mean ICP and pulse pressures of ICP are estimated from arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) waveforms, and the estimates are validated on an adult population, comprising of around two hours of data from five patients. The algorithm was shown to have an accuracy (mean error) of -1.5 mmHg and a precision (standard deviation of the error) of 4.3 mmHg in estimating the mean ICP. These results are comparable to the previously reported errors among the currently accepted invasive measurement methods, and well within the clinically relevant range.

Differentiate the Source and Site of Intracranial Pressure Measurements Using More Precise Nomenclature

BACKGROUND

Intracranial pressure (ICP) monitoring is fundamental for neurocritical care patient management. For many years, ventricular and parenchymal devices have been available for this aim. The purpose of this paper is to review the published literature comparing ICP recordings via an intraventricular catheter or an intraparenchymal (brain tissue) catheter.

METHODS

Literature search of Medline, CINAHL, Embase, and Scopus was performed in which manuscripts discussed both ICP monitoring via an intraventricular catheter and ICP monitoring through intraparenchymal (brain tissue) catheter. Keywords and MeSH terms used include critical care, intracranial pressure, ICP, monitoring, epidural catheter, intracranial hypertension, ventriculostomy, ventricular drain, external ventricular drain, and physiologic monitoring.

RESULTS

Eleven articles met inclusion criteria. The published literature shows differences in simultaneously recorded ICP between the intraventricular and intraparenchymal sites.

CONCLUSIONS

We propose two new terms that more accurately identify the anatomical site of recording for the referenced ICP: intracranial pressure ventricular (ICP-v) and intracranial pressure brain tissue (ICP-bt). Further delineation of the conventional term "ICP" into these two new terms will clarify the difference between ICP-v and ICP-bt and their respective measurement locations.

Pseudo-Bayesian Model-Based Noninvasive Intracranial Pressure Estimation and Tracking

OBJECTIVE

A noninvasive intracranial pressure (ICP) estimation method is proposed that incorporates a model-based approach within a probabilistic framework to mitigate the effects of data and modeling uncertainties.

METHODS

A first-order model of the cerebral vasculature relates measured arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) to ICP. The model is driven by the ABP waveform and is solved for a range of mean ICP values to predict the CBFV waveform. The resulting errors between measured and predicted CBFV are transformed into likelihoods for each candidate ICP in two steps. First, a baseline ICP estimate is established over five data windows of 20 beats by combining the likelihoods with a prior distribution of the ICP to yield an a posteriori distribution whose median is taken as the baseline ICP estimate. A single-state model of cerebral autoregulatory dynamics is then employed in subsequent data windows to track changes in the baseline by combining ICP estimates obtained with a uniform prior belief and model-predicted ICP. For each data window, the estimated model parameters are also used to determine the ICP pulse pressure.

RESULTS

On a dataset of thirteen pediatric patients with a variety of pathological conditions requiring invasive ICP monitoring, the method yielded for mean ICP estimation a bias (mean error) of 0.6 mmHg and a root-mean-squared error of 3.7 mmHg.

CONCLUSION

These performance characteristics are well within the acceptable range for clinical decision making.

SIGNIFICANCE

The method proposed here constitutes a significant step towards robust, continuous, patient-specific noninvasive ICP determination.

Intracranial pressure monitoring: Gold standard and recent innovations

Intracranial pressure monitoring (ICP) is based on the doctrine proposed by Monroe and Kellie centuries ago. With the advancement of technology and science, various invasive and non-invasive modalities of monitoring ICP continue to be developed. An ideal monitor to track ICP should be easy to use, accurate, reliable, reproducible, inexpensive and should not be associated with infection or haemorrhagic complications. Although the transducers connected to the extra ventricular drainage continue to be Gold Standard, its association with the likelihood of infection and haemorrhage have led to the search for alternate non-invasive methods of monitoring ICP. While Camino transducers, Strain gauge micro transducer based ICP monitoring devices and the Spiegelberg ICP monitor are the emerging technology in invasive ICP monitoring, optic nerve sheath diameter measurement, venous opthalmodynamometry, tympanic membrane displacement, tissue resonance analysis, tonometry, acoustoelasticity, distortion-product oto-acoustic emissions, trans cranial doppler, electro encephalogram, near infra-red spectroscopy, pupillometry, anterior fontanelle pressure monitoring, skull elasticity, jugular bulb monitoring, visual evoked response and radiological based assessment of ICP are the non-invasive methods which are assessed against the gold standard.

Best zero level for external ICP transducer

BACKGROUND

Continuous monitoring of intracranial pressure (ICP) was introduced in the 1950s. For correct ICP recordings, the zero-reference point for the external pressure gauge must be placed next to a head anatomical structure. We evaluated different anatomical points as zero reference for the ICP device at different head positions and their relation to brain centre (BC), foramen of Monro (Monro), and brain surface.

METHODS

Patients referred for neuroimaging due to e.g. headache all having normal 3D MRI scans were selected. Monro, BC, Orbit(O), external auditory meatus (EAM), and orbito-meatal (OM) line were identified and projected to mid-sagittal, or axial images. Each scan was evaluated like lying supine, 45° head elevations, upright, and 45° lateral position. Distances from skin to brain surface, BC, and Monro were measured. All values are presented as mean ± SD and/or range in millimetre. For conversion to mmHg, millimetre was multiplied by 0.074.

RESULTS

Twenty MRI scans were examined. A zero reference at EAM or glabella was ideal at BC when head was strict supine or in the lateral position. At 45° head elevation, an overestimation of the BC-ICP by 4.8 ± 0.8 and in upright 5.6 ± 0.5 mmHg was found, and 45° lateral underestimated ICP-BC by 6.3 ± 1.0 mmHg. Monro was situated 45 ± 5 mm rostral to the mid-OM line and 24 (18-31) mm inferior and 13 (8-17) mm in front of BC. A zero-reference point aligned with the highest point of the head underestimated BC-ICP and Monro-ICP. If the ICP reading was added 5.9 or 6.3 mmHg, respectively, a deviation from BC-ICP was ≤ 1.8 mmHg and Monro-ICP was ≤ 0.9 mmHg in all head positions.

CONCLUSIONS

EAM and glabella are defined anatomical structures representing BC when strict supine or lateral but with 12 mmHg variation with different head positions used in clinical practice. The OM line follows Monro at head elevation, but not when the head is turned. When the highest external point on the head is used, ICP values at brain surface as well as Monro and BC are underestimated. This underestimation is fairly constant and, when corrected for, provides the most exact ICP reading.

Intracranial pressure monitoring in normal dogs using subdural and intraparenchymal miniature strain-gauge transducers

Background

Monitoring of intracranial pressure (ICP) is a critical component in the management of intracranial hypertension. Safety, efficacy, and optimal location of microsensor devices have not been defined in dogs.

Hypothesis/Objective

Assessment of ICP using a microsensor transducer is feasible in anesthetized and conscious animals and is independent of transducer location. Intraparenchymal transducer placement is associated with more adverse effects.

Animals

Seven adult, bred‐for‐research dogs.

Methods

In a prospective investigational study, microsensor ICP transducers were inserted into subdural and intraparenchymal locations at defined rostral or caudal locations within the rostrotentorial compartment under general anesthesia. Mean arterial pressure and ICP were measured continuously during physiological maneuvers, and for 20 hours after anesthesia.

Results

Baseline mean ± SD values for ICP and cerebral perfusion pressure were 7.2 ± 2.3 and 78.9 ± 7.6 mm Hg, respectively. Catheter position did not have a significant effect on ICP measurements. There was significant variation from baseline ICP accompanying physiological maneuvers (P < .001) and with normal activities, especially with changes in head position (P < .001). Pathological sequelae were more evident after intraparenchymal versus subdural placement.

Conclusions and Clinical Importance

Use of a microsensor ICP transducer was technically straightforward and provided ICP measurements within previously reported reference ranges. Results support the use of an accessible dorsal location and subdural positioning. Transient fluctuations in ICP are normal events in conscious dogs and large variations associated with head position should be accounted for when evaluating animals with intracranial hypertension.

Multimodality Monitoring in Neurocritical Care: Decision-Making Utilizing Direct And Indirect Surrogate Markers

Substantial progress has been made to create innovative technology that can monitor the different physiological characteristics that precede the onset of secondary brain injury, with the ultimate goal of intervening prior to the onset of irreversible neurological damage. One of the goals of neurocritical care is to recognize and preemptively manage secondary neurological injury by analyzing physiologic markers of ischemia and brain injury prior to the development of irreversible damage. This is helpful in a multitude of neurological conditions, whereby secondary neurological injury could present including but not limited to traumatic intracranial hemorrhage and, specifically, subarachnoid hemorrhage, which has the potential of progressing to delayed cerebral ischemia and monitoring postneurosurgical interventions. In this study, we examine the utilization of direct and indirect surrogate physiologic markers of ongoing neurologic injury, including intracranial pressure, cerebral blood flow, and brain metabolism.

Evaluation of a novel noninvasive ICP monitoring device in patients undergoing invasive ICP monitoring: preliminary results

OBJECTIVE There is no established method of noninvasive intracranial pressure (NI-ICP) monitoring that can serve as an alternative to the gold standards of invasive monitoring with external ventricular drainage or intraparenchymal monitoring. In this study a new method of NI-ICP monitoring performed using algorithms to determine ICP based on acoustic properties of the brain was applied in patients undergoing invasive ICP (I-ICP) monitoring, and the results were analyzed. METHODS In patients with traumatic brain injury and subarachnoid hemorrhage who were undergoing treatment in a neurocritical intensive care unit, the authors recorded ICP using the gold standard method of invasive external ventricular drainage or intraparenchymal monitoring. In addition, the authors simultaneously measured the ICP noninvasively with a device (the HS-1000) that uses advanced signal analysis algorithms for acoustic signals propagating through the cranium. To assess the accuracy of the NI-ICP method, data obtained using both I-ICP and NI-ICP monitoring methods were analyzed with MATLAB to determine the statistical significance of the differences between the ICP measurements obtained using NI-ICP and I-ICP monitoring. RESULTS Data were collected in 14 patients, yielding 2543 data points of continuous parallel ICP values in recordings obtained from I-ICP and NI-ICP. Each of the 2 methods yielded the same number of data points. For measurements at the ≥ 17-mm Hg cutoff, which was arbitrarily chosen for this preliminary analysis, the sensitivity and specificity for the NI-ICP monitoring were found to be 0.7541 and 0.8887, respectively. Linear regression analysis indicated that there was a strong positive relationship between the measurements. Differential pressure between NI-ICP and I-ICP was within ± 3 mm Hg in 63% of data-paired readings and within ± 5 mm Hg in 85% of data-paired readings. The receiver operating characteristic-area under the curve analysis revealed that the area under the curve was 0.895, corresponding to the overall performance of NI-ICP monitoring in comparison with I-ICP monitoring. CONCLUSIONS This study provides the first clinical data on the accuracy of the HS-1000 NI-ICP monitor, which uses advanced signal analysis algorithms to evaluate properties of acoustic signals traveling through the brain in patients undergoing I-ICP monitoring. The findings of this study highlight the capability of this NI-ICP device to accurately measure ICP noninvasively. Further studies should focus on clinical validation for elevated ICP values.

Intracranial Multimodality Monitoring for Delayed Cerebral Ischemia

Management of patients with aneurysmal subarachnoid hemorrhage focuses on prevention of rebleeding by early treatment of the aneurysm, as well as detection and management of neurologic and medical complications. Early detection of delayed cerebral ischemia and management of modifiable contributing causes such as vasospasm take a central role, with the goal of preventing irreversible cerebral injury. In efforts to prevent delayed cerebral ischemia, multimodality monitoring has emerged as a promising tool in detecting subclinical physiologic changes before infarction occurs. However, there has been much variability in the utilization of this technology. Recent consensus guidelines discuss the role of multimodality monitoring in acute brain injury. In this review, we evaluate these guidelines and the utility of each modality of multimodality monitoring in aneurysmal subarachnoid hemorrhage.

Brain Multimodality Monitoring: Updated Perspectives

The challenges posed by acute brain injury (ABI) involve the management of the initial insult in addition to downstream inflammation, edema, and ischemia that can result in secondary brain injury (SBI). SBI is often subclinical, but can be detected through physiologic changes. These changes serve as a surrogate for tissue injury/cell death and are captured by parameters measured by various monitors that measure intracranial pressure (ICP), cerebral blood flow (CBF), brain tissue oxygenation (PbtO2), cerebral metabolism, and electrocortical activity. In the ideal setting, multimodality monitoring (MMM) integrates these neurological monitoring parameters with traditional hemodynamic monitoring and the physical exam, presenting the information needed to clinicians who can intervene before irreversible damage occurs. There are now consensus guidelines on the utilization of MMM, and there continue to be new advances and questions regarding its use. In this review, we examine these recommendations, recent evidence for MMM, and future directions for MMM.

Increasing Intracranial Pressure After Head Injury: Impact on Respiratory Oscillations in Cerebral Blood Flow Velocity

Experiments have shown that closed-box conditions alter the transmission of respiratory oscillations (R waves) to organ blood flow already at a marginal pressure increase. How does the increasing intracranial pressure (ICP) interact with R waves in cerebral blood flow after head injury (HI)?Twenty-two head-injured patients requiring sedation and mechanical ventilation were monitored for ICP, Doppler flow velocity (FV) in the middle cerebral arteries, and arterial blood pressure (ABP). The analysis included transfer function gains of R waves (9-20 cpm) from ABP to FV, and indices of pressure-volume reserve (RAP) and autoregulation (Mx). Increasing ICP has dampened R-wave gains from day 1 to day 4 after HI in all patients. A large impact (ΔGain /ΔICP right: 0.14 ± 0.06; left: 0.18 ± 0.08) was associated with exhausted reserves (RAP ≥0.85). When RAP was <0.85, rising ICP had a lower impact on R-wave gains (ΔGain /ΔICP right: 0.05 ± 0.02; left: 0.06 ± 0.04; p < 0.05), but increased the pulsatility indices (right: 1.35 ± 0.55; left: 1.25 ± 0.52) and Mx indices (right: 0.30 ± 0.12; left: 0.28 ± 0.08, p < 0.05). Monitoring of R waves in blood pressure and cerebral blood flow velocity has suggested that rising ICP after HI might have an impact on cerebral blood flow directly, even before autoregulation is impaired.

Clinical Validation of a Transcranial Doppler-Based Noninvasive Intracranial Pressure Meter: A Prospective Cross-Sectional Study

BACKGROUND

Noninvasive intracranial pressure (ICP) measurement would represent a major advance for patients with neurological problems. The Vittamed ICP meter is an ultrasound-based device reported to have high agreement with lumbar puncture cerebrospinal fluid (CSF) pressure measurement. However, previous studies included mostly patients with normal levels of ICP. The purpose of our study was to perform an independent clinical validation study of a transcranial Doppler-based noninvasive ICP meter in patients anticipated to have a wide range of ICP.

METHODS

In a prospective cross-sectional design, we simultaneously measured ICP with the Vittamed device and the invasive lumbar CSF pressure. The operator of each procedure was blinded to the result of the other method. Data were analyzed using Bland-Altman plots, Pearson correlation coefficients, and receiver operator characteristic curves.

RESULTS

Twenty-four independent paired measurements of Vittamed and lumbar CSF pressure were obtained; with mean absolute difference between paired measures of 4.5 mmHg (standard deviation 3.1). The 95% limits of agreement were -10.5 to +11.0. The systematic bias (mean of paired differences) was negligible at 0.25 mmHg. The sensitivity, specificity, and area under the curve for ICP >20 mmHg were 0.73, 0.77, and 0.71, respectively.

CONCLUSIONS

The Vittamed ICP meter had fair agreement with lumbar CSF pressure measurement. The wide limits of agreement would preclude using this version of the device as a stand-alone method for ICP determination, but may be useful if combined with other ICP screening methods. Ongoing improvements to the Vittamed hardware and software may lead to improvements in accuracy and clinical utility of this device.

Accuracy of intracranial pressure monitoring: systematic review and meta-analysis

Introduction

Intracranial pressure (ICP) measurement is used to tailor interventions and to assist in formulating the prognosis for traumatic brain injury patients. Accurate data are therefore essential. The aim of this study was to verify the accuracy of ICP monitoring systems on the basis of a literature review.

Methods

A PubMed search was conducted from 1982 to 2014, plus additional references from the selected papers. Accuracy was defined as the degree of correspondence between the pressure read by the catheter and a reference “real” ICP measurement. Studies comparing simultaneous readings from at least two catheters were included. Drift was defined as the loss of accuracy over the monitoring period. Meta-analyses of data from the studies were used to estimate the overall mean difference between simultaneous ICP measurements and their variability. Individual studies were weighted using both a fixed and a random effects model.

Results

Of 163 articles screened, 83 compared two intracranial catheters: 64 reported accuracy and 37 drift (some reported both). Of these, 10 and 17, respectively, fulfilled the inclusion criteria for accuracy and zero drift analysis. The combined mean differences between probes were 1.5 mmHg (95 % confidence interval (CI) 0.7–2.3) with the random effects model and 1.6 mmHg (95 % CI 1.3–1.9) with the fixed effects model. The reported mean drift over a long observation period was 0.75 mmHg. No relation was found with the duration of monitoring or differences between various probes.

Conclusions

This study confirms that the average error between ICP measures is clinically negligible. The random effects model, however, indicates that a high percentage of readings may vary over a wide range, with clinical implications both for future comparison studies and for daily care.

Intracranial pressure and cerebral perfusion pressure monitoring in non-TBI patients: special considerations

The effect of intracranial pressure (ICP) and the role of ICP monitoring are best studied in traumatic brain injury (TBI). However, a variety of acute neurologic illnesses e.g., subarachnoid hemorrhage, intracerebral hemorrhage, ischemic stroke, meningitis/encephalitis, and select metabolic disorders, e.g., liver failure and malignant, brain tumors can affect ICP. The purpose of this paper is to review the literature about ICP monitoring in conditions other than TBI and to provide recommendations how the technique may be used in patient management. A PubMed search between 1980 and September 2013 identified 989 articles; 225 of which were reviewed in detail. The technique used to monitor ICP in non-TBI conditions is similar to that used in TBI; however, indications for ICP monitoring often are intertwined with the presence of obstructive hydrocephalus and hence the use of ventricular catheters is more frequent. Increased ICP can adversely affect outcome, particularly when it fails to respond to treatment. However, patients with elevated ICP can still have favorable outcomes. Although the influence of ICP-based care on outcome in non-TBI conditions appears less robust than in TBI, monitoring ICP and cerebral perfusion pressure can play a role in guiding therapy in select patients.

Intracranial pressure monitoring: fundamental considerations and rationale for monitoring

Traumatic brain injury (TBI) is a major cause of death and disability worldwide. In large part critical care for TBI is focused on the identification and management of secondary brain injury. This requires effective neuromonitoring that traditionally has centered on intracranial pressure (ICP). The purpose of this paper is to review the fundamental literature relative to the clinical application of ICP monitoring in TBI critical care and to provide recommendations on how the technique maybe applied to help patient management and enhance outcome. A PubMed search between 1980 and September 2013 identified 2,253 articles; 244 of which were reviewed in detail to prepare this report and the evidentiary tables. Several important concepts emerge from this review. ICP monitoring is safe and is best performed using a parenchymal monitor or ventricular catheter. While the indications for ICP monitoring are well established, there remains great variability in its use. Increased ICP, particularly the pattern of the increase and ICP refractory to treatment is associated with increased mortality. Class I evidence is lacking on how monitoring and management of ICP influences outcome. However, a large body of observational data suggests that ICP management has the potential to influence outcome, particularly when care is targeted and individualized and supplemented with data from other monitors including the clinical examination and imaging.

Optical Fibre Pressure Sensors in Medical Applications

This article is focused on reviewing the current state-of-the-art of optical fibre pressure sensors for medical applications. Optical fibres have inherent advantages due to their small size, immunity to electromagnetic interferences and their suitability for remote monitoring and multiplexing. The small dimensions of optical fibre-based pressure sensors, together with being lightweight and flexible, mean that they are minimally invasive for many medical applications and, thus, particularly suited to in vivo measurement. This means that the sensor can be placed directly inside a patient, e.g., for urodynamic and cardiovascular assessment. This paper presents an overview of the recent developments in optical fibre-based pressure measurements with particular reference to these application areas.

Comparison of parenchymal and ventricular intracranial pressure readings utilizing a novel multi-parameter intracranial access system

Introduction

Both ventricular and parenchymal devices are available for measurement of intracranial pressure (ICP). The Hummingbird^® Synergy Ventricular System is a novel device allowing multi-parametric neurological monitoring, including both ventricular and parenchymal ICP. The purpose of this study is to compare the congruence of the device’s ventricular and parenchymal ICP readings.

Methods

This single-center, quantitative, interventional study compared parenchymal and ventricular ICP readings from 35 patients with the Hummingbird^® System. If a difference of > ± 3 mmHg existed between an individual patient’s parenchymal and ventricular values, progressive intervention strategies were applied to correct identified issues.

Results

From a total of 2,259 observations, statistical analysis revealed congruence (within ±0-3 mmHg) of 93% of readings comparing parenchymal and ventricular ICP. Of the observations requiring intervention, 58% involved the parenchymal component, 30% involved the ventricular component, and 12% involved both components. Following prescribed interventions, 98% of readings became congruent (within ±0-3 mmHg). The adjusted mean difference between the two methods was -0.95 (95% CI: -0.97,-0.93) mmHg and all mean ICP readings fell between -2 and 2 mmHg.

Conclusion

The Hummingbird^® Synergy Ventricular System demonstrates congruence between ventricular and parenchymal ICP measurements within accepted parameters. Interventions required to realign parenchymal and ventricular readings serve as reminders to clinicians to be vigilant with catheter/cable connections and to maintain appropriate positioning of the ventricular drainage system. The results of this study support the recommendation to use the parenchymal ICP component for routine ICP monitoring, allowing dedication of the ventricular catheter to drainage of cerebrospinal fluid (CSF).

Traumatic brain injury: increasing ICP attenuates respiratory modulations of cerebral blood flow velocity

In vitro experiments have suggested that respiratory oscillations (R waves) in cerebral blood flow velocity are reduced as soon as the intracranial pressure-volume reserve is exhausted. Could R waves hence, provide indication for increasing ICP after traumatic brain injury (TBI)? On days 1 to 4 after TBI, 22 sedated and ventilated patients were monitored for intracranial pressure (ICP) in brain parenchyma, Doppler flow velocity (FV) in the middle cerebral arteries (MCA), and arterial blood pressure (ABP). The analysis included the transfer function gains of R waves (respiratory rate of 9-20 cpm) between ABP and FV (GainFv) as well as between ABP and ICP (GainICP). Also, the index of the intracranial pressure-volume reserve (RAP) was calculated. The rise of ICP (day 1: 14.10 ± 6.22 mmHg; to day 4: 29.69 ± 12.35 mmHg) and increase of RAP (day 1: 0.72 ± 0.22; to day 4: 0.85 ± 0.18) were accompanied by a decrease of GainFv (right MCA; day 1: 1.78 ± 1.0; day 4: 0.84 ± 0.47; left MCA day 1: 1.74 ± 1.10; day 4: 0.86 ± 0.46; p < 0.01) but no significant change in GainICP day 1: 1.50 ± 0.77; day 4: 1.15 ± 0.47; p = 0.07). The transfer of ventilatory oscillations to the intracerebral arteries after TBI appears to be dampened by increasing ICP and exhausted intracranial pressure-volume reserves. Results warrant prospective studies of whether respiratory waves in cerebral blood flow velocity may anticipate intracranial hypertension non-invasively.

Evaluation of a new large animal model for controlled intracranial pressure changes induced by capnoperitoneum

BACKGROUND

A standardized large animal model for controlled ICP manipulation within a relevant range and repetitive ICP measurements is missing. We sought to develop such a model on the base of controlled IPP changes induced by capnoperitoneum.

METHODS

We utilized six female pigs (mean body weight 59.5 ± 18.4 kg) for experiments. A ventricular catheter connected with a burr hole reservoir was implanted. ICP was measured directly as cm H2O within a riser tube after percutaneous cannulation of the reservoir. A noninvasive intraperitoneal pressure (IPP) measurement was established (intravesical). Animals were placed in lateral position and a capnoperitoneum was induced. Measurements of ICP, IPP, MAP and respiratory parameters were performed at baseline IPP and after CO2 insufflation to IPP levels of 20 and 30 mmHg.

RESULTS

Baseline IPP in lateral position referenced to median line was 9.8 (±2) mm Hg, while corresponding ICP was 10 (±2.2) mm Hg. After IPP elevation to 20 mmHg, ICP increased to 18.8 (±1.9) mm Hg. At 30 mmHg IPP, ICP increased to 22.8 (±2.8) mm Hg. Except peak airway pressure, all other parameters were kept constantly. Mean ICP variation in the individual subject was 13.4 (±2.5) mm Hg, while a ICP range from minimum 9 to maximum 31 mmHg was documented.

CONCLUSIONS

We report a large animal model that allows (1) repeated measurement of the ICP and (2) manipulation of the ICP within a large pressure range by controlled IPP changes due to capnoperitoneum.

Intracranial Pressure Monitoring: Invasive versus Non-Invasive Methods-A Review

Monitoring of intracranial pressure (ICP) has been used for decades in the fields of neurosurgery and neurology. There are multiple techniques: invasive as well as noninvasive. This paper aims to provide an overview of the advantages and disadvantages of the most common and well-known methods as well as assess whether noninvasive techniques (transcranial Doppler, tympanic membrane displacement, optic nerve sheath diameter, CT scan/MRI and fundoscopy) can be used as reliable alternatives to the invasive techniques (ventriculostomy and microtransducers). Ventriculostomy is considered the gold standard in terms of accurate measurement of pressure, although microtransducers generally are just as accurate. Both invasive techniques are associated with a minor risk of complications such as hemorrhage and infection. Furthermore, zero drift is a problem with selected microtransducers. The non-invasive techniques are without the invasive methods' risk of complication, but fail to measure ICP accurately enough to be used as routine alternatives to invasive measurement. We conclude that invasive measurement is currently the only option for accurate measurement of ICP.