Intracranial Compliance Assessed by Intracranial Pressure Pulse Waveform

Validation of a Noninvasive Approach for Cerebrospinal Compliance Monitoring

BACKGROUND

Intracranial pressure (ICP) monitoring is a cornerstone of neurointensive care. However, some limitations of invasive techniques for ICP monitoring to acknowledge are the risk for complications and the lack of robust evidence supporting individualized ICP safety thresholds. Cerebrospinal compliance (CSC) may serve as a more reliable indicator of brain health than ICP alone. Previously, intracranial compliance (Ci), was described as a mathematical model from invasive ICP to assess CSC, using ICP waveform amplitudes and cerebral arterial blood volume (CaBV) waveform amplitudes via transcranial Doppler (TCD). This study aimed to compare Ci with a surrogate parameter based on CaBV waveform amplitudes and pulsatile micrometric skull waveforms (Skw) amplitudes. This noninvasive parameter was named Bcomp.

METHODS

Neurocritical patients undergoing ICP monitoring were evaluated using TCD and the skull micrometric deformation sensor (B4C). ICP waveform (from invasive ICP probes) and Skw (from noninvasive B4C) were analyzed to extract pulse amplitudes, whereas TCD provided cerebral blood velocities from the middle cerebral arteries for CaBV calculation. CSC was measured using the volume/pressure relationship, with CaBV amplitude serving as the volume surrogate, and ICP and B4C pulse amplitudes as surrogates for ICP values. Agreement and correlation analysis was calculated between Ci and Bcomp.

RESULTS

Data from 71 patients were analyzed, with 68% of the sample having suffered traumatic brain injury. Maximum CaBV was significantly delayed in patients with poor CSC (p < 0.001). Ci and Bcomp showed strong agreement and linear correlation (mean difference of - 0.28 and Spearman correlation of 0.88, p < 0.001).

CONCLUSIONS

Using CaBV, which reflects changes in arterial blood volume during the cardiac cycle and Skw pulse amplitudes, Bcomp demonstrated high agreement and correlation with Ci, defined as the product of CaBV and ICP pulse amplitude. The observed shift in CaBV among patients with poor CSC suggests that this vascular marker is influenced by intracranial resistance. These findings are promising for the real-time, noninvasive assessment of CSC in clinical settings and warrant further research.

Machine learning approach for noninvasive intracranial pressure estimation using pulsatile cranial expansion waveforms

Noninvasive methods for intracranial pressure (ICP) monitoring have emerged, but none has successfully replaced invasive techniques. This observational study developed and tested a machine learning (ML) model to estimate ICP using waveforms from a cranial extensometer device (brain4care [B4C] System). The model explored multiple waveform parameters to optimize mean ICP estimation. Data from 112 neurocritical patients with acute brain injuries were used, with 92 patients randomly assigned to training and testing, and 20 reserved for independent validation. The ML model achieved a mean absolute error of 3.00 mmHg, with a 95% confidence interval within ±7.5 mmHg. Approximately 72% of estimates from the validation sample were within 0-4 mmHg of invasive ICP values. This proof-of-concept study demonstrates that noninvasive ICP estimation via the B4C System and ML is feasible. Prospective studies are needed to validate the model's clinical utility across diverse settings.

Evolving concepts in intracranial pressure monitoring - from traditional monitoring to precision medicine

A wide range of acute brain injuries, including both traumatic and non-traumatic causes, can result in elevated intracranial pressure (ICP), which in turn can cause further secondary injury to the brain, initiating a vicious cascade of propagating injury. Elevated ICP is therefore a neurological injury that requires intensive monitoring and time-sensitive interventions. Patients at high risk for developing elevated ICP undergo placement of invasive ICP monitors including external ventricular drains, intraparenchymal ICP monitors, and lumbar drains. These monitors all generate an ICP waveform, but each has its own unique caveats in monitoring and accuracy. Current ICP monitoring and management clinical guidelines focus on the mean ICP derived from the ICP waveform, with standard thresholds of treating ICP greater than 20 ​mmHg or 22 ​mmHg applied broadly to a wide range of patients. However, this one-size fits all approach has been criticized and there is a need to develop personalized, evidence-based and possibly multi-factorial precision-medicine based approaches to the problem. This paper provides historical and physiological context to the problem of elevated ICP, provides an overview of the challenges of the current paradigm of ICP management strategies, and discusses advances in ICP waveform analysis, emerging non-invasive ICP monitoring techniques, and applications of machine learning to create predictive algorithms.

Cerebral compliance assessment from intracranial pressure waveform analysis: Is a positional shift-related increase in intracranial pressure predictable?

Real-time monitoring of intracranial pressure (ICP) is a routine part of neurocritical care in the management of brain injury. While mainly used to detect episodes of intracranial hypertension, the ICP signal is also indicative of the volume-pressure relationship within the cerebrospinal system, often referred to as intracranial compliance (ICC). Several ICP signal descriptors have been proposed in the literature as surrogates of ICC, but the possibilities of combining these are still unexplored. In the present study, a rapid ICC assessment consisting of a 30-degree postural shift was performed on a cohort of 54 brain-injured patients. 73 ICP signal features were calculated over the 20 minutes prior to the ICC test. After a selection step, different combinations of these features were provided as inputs to classification models. The goal was to predict the level of induced ICP elevation, which was categorized into three classes: less than 7 mmHg ("good ICC"), between 7 and 10 mmHg ("medium ICC"), and more than 10 mmHg ("poor ICC"). A logistic regression model fed with a combination of 5 ICP signal features discriminated the "poor ICC" class with an area under the receiving operator curve (AUROC) of 0.80 (95%-CI: [0.73-0.87]). The overall one-versus-one classification task was achieved with an averaged AUROC of 0.72 (95%-CI: [0.61-0.83]). Adding more features to the input set and/or using nonlinear machine learning algorithms did not significantly improve classification performance. This study highlights the potential value of analyzing the ICP signal independently to extract information about ICC status. At the patient's bedside, such univariate signal analysis could be implemented without dependence on a specific setup.

The Development of Non-Invasive Optical Brain Pulse Monitoring: A Review

Early detection of neurological deterioration in serious acute brain injury is seen as an important goal to reduce death and disability, but monitoring for neurological deterioration remains challenging. Routine methods, such as neurological examination and brain imaging, often identify brain injuries only after they have progressed to an irreversible stage. Alternate approaches such as invasive brain monitoring, are complex, costly and carry inherent risks. The optical brain pulse monitor (OBPM) is a novel, non-invasive, safe, and continuous monitoring device designed to provide earlier detection of neurological deterioration and address the limitations of traditional approaches. This review presents the development, technical aspects, and clinical results from past and ongoing trials over the last five years.

A Comprehensive Perspective on Intracranial Pressure Monitoring and Individualized Management in Neurocritical Care: Results of a Survey with Global Experts

BACKGROUND

Numerous trials have addressed intracranial pressure (ICP) management in neurocritical care. However, identifying its harmful thresholds and controlling ICP remain challenging in terms of improving outcomes. Evidence suggests that an individualized approach is necessary for establishing tolerance limits for ICP, incorporating factors such as ICP waveform (ICPW) or pulse morphology along with additional data provided by other invasive (e.g., brain oximetry) and noninvasive monitoring (NIM) methods (e.g., transcranial Doppler, optic nerve sheath diameter ultrasound, and pupillometry). This study aims to assess current ICP monitoring practices among experienced clinicians and explore whether guidelines should incorporate ancillary parameters from NIM and ICPW in future updates.

METHODS

We conducted a survey among experienced professionals involved in researching and managing patients with severe injury across low-middle-income countries (LMICs) and high-income countries (HICs). We sought their insights on ICP monitoring, particularly focusing on the impact of NIM and ICPW in various clinical scenarios.

RESULTS

From October to December 2023, 109 professionals from the Americas and Europe participated in the survey, evenly distributed between LMIC and HIC. When ICP ranged from 22 to 25 mm Hg, 62.3% of respondents were open to considering additional information, such as ICPW and other monitoring techniques, before adjusting therapy intensity levels. Moreover, 77% of respondents were inclined to reassess patients with ICP in the 18-22 mm Hg range, potentially escalating therapy intensity levels with the support of ICPW and NIM. Differences emerged between LMIC and HIC participants, with more LMIC respondents preferring arterial blood pressure transducer leveling at the heart and endorsing the use of NIM techniques and ICPW as ancillary information.

CONCLUSIONS

Experienced clinicians tend to personalize ICP management, emphasizing the importance of considering various monitoring techniques. ICPW and noninvasive techniques, particularly in LMIC settings, warrant further exploration and could potentially enhance individualized patient care. The study suggests updating guidelines to include these additional components for a more personalized approach to ICP management.

The Neurological and Hemodynamics Safety of an Airway Clearance Technique in Patients with Acute Brain Injury: An Analysis of Intracranial Pressure Pulse Morphology Using a Non-Invasive Sensor

Patients with acute brain injury (ACI) often require mechanical ventilation (MV) and are subject to pulmonary complications, thus justifying the use of Airway Clearance Techniques (ACTs), but their effects on intracranial pressure (ICP) are unknown. This study investigates the neurological and hemodynamics safety of an ACT called ventilator hyperinflation (VHI) in patients with ACI. This was a randomized clinical equivalence trial, which included patients aged ≥ 18 years with a clinical diagnosis of hemorrhagic stroke, with symptom onset within 48 h. The participants were randomly allocated to the Experimental Group (EG, n = 15), which underwent VHI followed by tracheal aspiration (TA), and the Control Group (CG, n = 15), which underwent TA only. Neurological safety was verified by analyzing the morphology of the ICP wave through the non-invasive B4C sensor, which detects bone deformation of the skull, resulting in a P2/P1 ratio and TTP, and hemodynamics through a multi-parameter monitor. Evaluations were recorded during five instances: T1 (baseline/pre-VHI), T2 (post-VHI and before TA), T3 (post-TA), T4 and T5 (monitoring 10 and 20 min after T3). The comparison between groups showed that there was no effect of the technique on the neurological variables with a mean P2/P1 ratio [F (4,112) = 1.871; p = 0.120; np2 = 0.063] and TTP [F (4,112) = 2.252; p = 0.068; np2 = 0.074], and for hemodynamics, heart rate [F (4,112) = 1.920; p = 0.112; np2 = 0.064] and mean arterial pressure [F(2.73, 76.57) = 0.799; p = 0.488; np2 = 0.028]. Our results showed that VHI did not pose a neurological or hemodynamics risk in neurocritical patients after ACI.

Noninvasive intracranial pressure profile in 31 patients submitted to fullendoscopic spine surgery

PURPOSE

Full-endoscopic spine surgery (FESS) is associated with specific complications, possibly linked to increased intracranial pressure (ICP) resulting from continuous saline infusion into the epidural space. This study aimed to assess the impact of saline irrigation and its correlation with noninvasively obtained ICP waveform changes.

METHODS

Patients undergoing FESS between January 2019 and November 2020 were included. Noninvasive ICP (n-ICP) monitoring utilized an extracranial strain sensor generating ICP waveforms, from which parameters P2/P1 ratio and time to peak (TTP) values were derived and correlated to irrigation and vital parameters. Documentation occurred at specific surgical intervals (M0-preoperatively; M1 to M4-intraoperatively; M5-postoperatively). Mixed-model analysis of variance and multiple comparisons tests were applied, with M0 as the baseline.

RESULTS

Among 31 enrolled patients, three experienced headaches unrelated to increased ICP at M5. The P2/P1 ratio and TTP decreased during surgery (p < 0.001 and p < 0.004, respectively). Compared to baseline, P2/P1 ratio and vital parameters remained significantly lower at M5. No significant differences were observed for fluid parameters throughout surgery.

CONCLUSIONS

This study demonstrated a decline in the n-ICP parameters after anesthetic induction despite the anticipated increase in ICP due to constant epidural irrigation. The n-ICP parameters behaved independently of fluid parameters, suggesting a potential protective effect of anesthesia.

ICP wave morphology as a screening test to exclude intracranial hypertension in brain-injured patients: a non-invasive perspective

Intracranial hypertension (IH) is a life-threating condition especially for the brain injured patient. In such cases, an external ventricular drain (EVD) or an intraparenchymal bolt are the conventional gold standard for intracranial pressure (ICPi) monitoring. However, these techniques have several limitations. Therefore, identifying an ideal screening method for IH is important to avoid the unnecessary placement of ICPi and expedite its introduction in patients who require it. A potential screening tool is the ICP wave morphology (ICPW) which changes according to the intracranial volume-pressure curve. Specifically, the P2/P1 ratio of the ICPW has shown promise as a triage test to indicate normal ICP. In this study, we propose evaluating the noninvasive ICPW (nICPW-B4C sensor) as a screening method for ICPi monitoring in patients with moderate to high probability of IH. This is a retrospective analysis of a prospective, multicenter study that recruited adult patients requiring ICPi monitoring from both Federal University of São Paulo and University of São Paulo Medical School Hospitals. ICPi values and the nICPW parameters were obtained from both the invasive and the noninvasive methods simultaneously 5 min after the closure of the EVD drainage. ICP assessment was performed using a catheter inserted into the ventricle and connected to a pressure transducer and a drainage system. The B4C sensor was positioned on the patient's scalp without the need for trichotomy, surgical incision or trepanation, and the morphology of the ICP waves acquired through a strain sensor that can detect and monitor skull bone deformations caused by changes in ICP. All patients were monitored using this noninvasive system for at least 10 min per session. The area under the curve (AUC) was used to describe discriminatory power of the P2/P1 ratio for IH, with emphasis in the Negative Predictive value (NPV), based on the Youden index, and the negative likelihood ratio [LR-]. Recruitment occurred from August 2017 to March 2020. A total of 69 patients fulfilled inclusion and exclusion criteria in the two centers and a total of 111 monitorizations were performed. The mean P2/P1 ratio value in the sample was 1.12. The mean P2/P1 value in the no IH population was 1.01 meanwhile in the IH population was 1.32 (p < 0.01). The best Youden index for the mean P2/P1 ratio was with a cut-off value of 1.13 showing a sensitivity of 93%, specificity of 60%, and a NPV of 97%, as well as an AUC of 0.83 to predict IH. With the 1.13 cut-off value for P2/P1 ratio, the LR- for IH was 0.11, corresponding to a strong performance in ruling out the condition (IH), with an approximate 45% reduction in condition probability after a negative test (ICPW). To conclude, the P2/P1 ratio of the noninvasive ICP waveform showed in this study a high Negative Predictive Value and Likelihood Ratio in different acute neurological conditions to rule out IH. As a result, this parameter may be beneficial in situations where invasive methods are not feasible or unavailable and to screen high-risk patients for potential invasive ICP monitoring.Trial registration: At clinicaltrials.gov under numbers NCT05121155 (Registered 16 November 2021-retrospectively registered) and NCT03144219 (Registered 30 September 2022-retrospectively registered).

Continuous monitoring methods of cerebral compliance and compensatory reserve: a scoping review of human literature

Objective.Continuous monitoring of cerebrospinal compliance (CC)/cerebrospinal compensatory reserve (CCR) is crucial for timely interventions and preventing more substantial deterioration in the context of acute neural injury, as it enables the early detection of abnormalities in intracranial pressure (ICP). However, to date, the literature on continuous CC/CCR monitoring is scattered and occasionally challenging to consolidate.Approach.We subsequently conducted a systematic scoping review of the human literature to highlight the available continuous CC/CCR monitoring methods.Main results.This systematic review incorporated a total number of 76 studies, covering diverse patient types and focusing on three primary continuous CC or CCR monitoring metrics and methods-Moving Pearson's correlation between ICP pulse amplitude waveform and ICP, referred to as RAP, the Spiegelberg Compliance Monitor, changes in cerebral blood flow velocity with respect to the alternation of ICP measured through transcranial doppler (TCD), changes in centroid metric, high frequency centroid (HFC) or higher harmonics centroid (HHC), and the P2/P1 ratio which are the distinct peaks of ICP pulse wave. The majority of the studies in this review encompassed RAP metric analysis (n= 43), followed by Spiegelberg Compliance Monitor (n= 11), TCD studies (n= 9), studies on the HFC/HHC (n= 5), and studies on the P2/P1 ratio studies (n= 6). These studies predominantly involved acute traumatic neural injury (i.e. Traumatic Brain Injury) patients and those with hydrocephalus. RAP is the most extensively studied of the five focused methods and exhibits diverse applications. However, most papers lack clarification on its clinical applicability, a circumstance that is similarly observed for the other methods.Significance.Future directions involve exploring RAP patterns and identifying characteristics and artifacts, investigating neuroimaging correlations with continuous CC/CCR and integrating machine learning, holding promise for simplifying CC/CCR determination. These approaches should aim to enhance the precision and accuracy of the metric, making it applicable in clinical practice.

Improved Transcranial Doppler Waveform Analysis for Intracranial Hypertension Assessment in Patients with Traumatic Brain Injury

BACKGROUND

Transcranial Doppler (TCD) is a noninvasive bedside tool for cerebral hemodynamic assessments in multiple clinical scenarios. TCD, by means of measuring systolic and diastolic blood velocities, allows the calculation of the pulsatility index (PI), a parameter that is correlated with intracranial pressure (ICP). Nevertheless, the predictive value of the PI for raised ICP appears to be low, as it is subjected to several, often confounding, factors not related to ICP. Recently, the pulsatile apparent resistance (PaR) index was developed as a PI corrected for arterial blood pressure, reducing some of the confounding factors influencing PI. This study compares the predictive value of PaR versus PI for intracranial hypertension (IH) (ICP > 20 mm Hg) in patients with traumatic brain injury.

METHODS

Patients with traumatic brain injury admitted to the neurocritical care unit who required invasive ICP monitoring were included prospectively within 5 days of admission. TCD measurements were performed in both middle cerebral arteries, allowing calculations of the PI and PaR. The optimal cutoff, discriminative power of these parameters for ICP ≥ 20 mm Hg, was assessed by calculating the area under the receiver operator characteristics curve (AUC).

RESULTS

In total, 93 patients were included. A total of 20 (22%) patients experienced IH during the recording sessions. The discriminative power was low for PI (AUC 0.63) but slightly higher for PaR (AUC 0.77). Nonparametric analysis indicated significant difference for PaR when comparing patients with (median 0.169) and without IH (median - 0.052, p = 0.001), whereas PI medians for patients with and without IH were 0.86 and 0.77, respectively (p =  0.041). Regarding subanalyses, the discriminative power of these parameters increased after exclusion of patients who had undergone a neurosurgical procedure. This was especially true for the PaR (AUC 0.89) and PI (AUC 0.72). Among these patients, a PaR cutoff value of - 0.023 had 100% sensitivity and 52.9% specificity.

CONCLUSIONS

In the present study, discriminative power of the PaR for discriminating IH was superior to the PI. The PaR seems to be a reliable noninvasive parameter for detecting IH. Further studies are warranted to define its clinical application, especially in aiding neurosurgical decision making, following up in intensive care units, and defining its ability to indicate responses according to the therapies administered.

Cerebrovascular Responses in a Patient with Lundberg B Waves Following Subarachnoid Haemorrhage Assessed with a Novel Non-Invasive Brain Pulse Monitor: A Case Report

Subarachnoid haemorrhage (SAH) can trigger a range of poorly understood cerebrovascular responses that may play a role in delayed cerebral ischemia. The brain pulse monitor is a novel non-invasive device that detects a brain photoplethysmography signal that provides information on intracranial pressure (ICP), compliance, blood flow and tissue oxygen saturation. We monitored the cerebrovascular responses in a patient with Lundberg B waves following a SAH. The patient presented with a Fischer grade 4 SAH that required urgent left posterior communicating artery aneurysm coiling and ventricular drain insertion. On hospital day 4 oscillations or spikes on the invasive ICP were noted, consistent with Lundberg B waves. Brain pulse monitoring demonstrated concurrent pulse waveform features consistent with reduced brain compliance and raised ICP over both brain hemispheres. Oxygen levels also demonstrated slow oscillations correlated with the ICP spikes. Brief infrequent episodes of reduced and absent brain pulses were also noted over the right hemisphere. Our findings suggest that the brain pulse monitor holds promise for early detection of delayed cerebral ischemia and could offer insights into the vascular mechanisms at play.

Non-invasive Intracranial Pressure Waveform Analysis in Chiari Malformation Type 1: A Pilot Trial

OBJECTIVE

This pilot study aimed to investigate the role of Posterior Fossa Decompression (PFD) on the intracranial pressure (ICP) waveform in patients with Chiari Malformation type 1 (CM1). It also sought to explore the relationship between symptom improvement and ICP waveform behavior.

METHODS

This exploratory cohort study evaluated adult patients diagnosed with CM1. The patients underwent PFD using a standard technique at our institution, which involved a 3 × 3 cm posterior craniectomy and excision of the posterior arch of C1. The ICP waveform was measured using an external strain-gauge device connected to a pin attached to the skull. Measurements were collected pre- and post-PFD, and the P2/P1 ratio was calculated pre- and postoperatively.

RESULTS

The pilot study comprised 6 participants, 3 men and 3 women, with ages ranging from 39 to 68 years. The primary symptoms were cerebellar ataxia and typical headaches. The study found that most patients who showed clinical improvement, as judged by the Gestalt method, had a postoperative decrease in the P2/P1 ratio. However, 1 patient did not show an improvement in the P2/P1 ratio despite a good clinical outcome.

CONCLUSIONS

This study suggests that the P2/P1 ratio may decrease after PFD. However, we highlight the need for further research with a larger sample size to confirm these preliminary results.

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.

Influence of head-over-body and body-over-head posture on craniospinal, vascular, and abdominal pressures in an acute ovine in-vivo model

INTRODUCTION

Optimal shunt-based hydrocephalus treatments are heavily influenced by dynamic pressure behaviors between proximal and distal ends of shunt catheters. Posture-dependent craniospinal, arterial, venous, and abdominal dynamics thereby play an essential role.

METHODS

An in-vivo ovine trial (n = 6) was conducted to evaluate communication between craniospinal, arterial, venous, and abdominal dynamics. Tilt-testing was performed between -13° and + 13° at 10-min intervals starting and ending at 0° prone position. Mean pressure, pulse pressure, and Pearson correlation (r) to the respective angle were calculated. Correlations are defined as strong: |r|≥ 0.7, mild: 0.3 <|r|< 0.7, and weak: |r|≤ 0.3. Transfer functions (TFs) between the arterial and adjacent compartments were derived.

RESULTS

Strong correlations were observed between posture and: mean carotid/femoral arterial (r = - 0.97, r = - 0.87), intracranial, intrathecal (r = - 0.98, r = 0.94), jugular (r = - 0.95), abdominal cranial, dorsal, caudal, and intravesical pressure (r = - 0.83, r = 0.84, r = - 0.73, r = 0.99) while mildly positive correlation exists between tilt and central venous pressure (r = 0.65). Only dorsal abdominal pulse pressure yielded a significant correlation to tilt (r = 0.21). TFs followed general lowpass behaviors with resonant peaks at 4.2 ± 0.4 and 11.5 ± 1.5 Hz followed by a mean roll-off of - 15.9 ± 6.0 dB/decade.

CONCLUSIONS

Tilt-tests with multi-compartmental recordings help elucidate craniospinal, arterial, venous, and abdominal dynamics, which is essential to optimize shunt-based therapy. Results motivate hydrostatic influences on mean pressure, with all pressures correlating to posture, with little influence on pulse pressure. TF results quantify the craniospinal, arterial, venous, and abdominal compartments as compliant systems and help pave the road for better quantitative models of the interaction between the craniospinal and adjacent spaces.

Can a new noninvasive method for assessment of intracranial pressure predict intracranial hypertension and prognosis?

PURPOSE

Individuals with TBI are at risk of intracranial hypertension (ICH), and monitoring of intracranial pressure (ICP) is usually indicated. However, despite many new noninvasive devices, none is sufficiently accurate and effective for application in clinical practice, particularly in the management of TBIs. This study aimed to compare the noninvasive Brain4Care system (nICP) with invasive ICP (iICP) curve parameters in their ability to predict ICH and functional prognosis in severe TBI.

METHODS

Observational, descriptive-analytical, and prospective study of 22 patients between 2018 and 2021, simultaneously monitored with nICP and iICP. The independent variables evaluated were the presence of ICH and functional prognoses. The dependent variables were the P2/P1 pressure ratio metrics, time to peak (TTP), and TTP × P2/P1.

RESULTS

We found a good nonlinear correlation between iICP and nICP waveforms, despite a moderate Pearson's linear correlation. The noninvasive parameters of P2/P1, P2/P1 × TTP, and TTP were not associated with outcomes or ICH. The nICP P2/P1 ratio showed sensitivity/specificity/accuracy (%) of 100/0/56.3, respectively for 1-month outcomes and 77.8/22.2/50 for 6-month outcomes. The nICP TTP ratio had values of 100/0/56.3 for 1-month and 99.9/42.9/72.2 for 6-month outcomes. The nICP P2/P1 × TTP values were 100/0/56.3 for 1-month outcomes and 81.8/28.6/61.1 for 6-month outcomes.

CONCLUSION

Brain4Care's noninvasive method showed low specificity and accuracy and cannot be used as the sole means of monitoring ICP in patients with severe TBI. Future studies with a larger sample of patients with P2 > P1 and new nICP curve parameters are warranted.

Contribution of intracranial pressure to human dynamic cerebral autoregulation after acute brain injury

Cerebral perfusion pressure (CPP) is normally expressed by the difference between mean arterial blood pressure (MAP) and intracranial pressure (ICP) but comparison of the separate contributions of MAP and ICP to human cerebral blood flow autoregulation has not been reported. In patients with acute brain injury (ABI), internal jugular vein compression (IJVC) was performed for 60 s. Dynamic cerebral autoregulation (dCA) was assessed in recordings of middle cerebral artery blood velocity (MCAv, transcranial Doppler), and invasive measurements of MAP and ICP. Patients were separated according to injury severity as having whole/undamaged skull, large fractures, or craniotomies, or following decompressive craniectomy. Glasgow coma score was not different for the three groups. IJVC induced changes in MCAv, MAP, ICP, and CPP in all three groups. The MCAv response to step changes in MAP and ICP expressed the dCA response to these two inputs and was quantified with the autoregulation index (ARI). In 85 patients, ARI was lower for the ICP input as compared with the MAP input (2.25 ± 2.46 vs. 3.39 ± 2.28; P < 0.0001), and particularly depressed in the decompressive craniectomy (DC) group (n = 24, 0.35 ± 0.62 vs. 2.21 ± 1.96; P < 0.0005). In patients with ABI, the dCA response to changes in ICP is less efficient than corresponding responses to MAP changes. These results should be taken into consideration in studies aimed to optimize dCA by manipulation of CPP in neurocritical patients.

The intracranial pressure-volume relationship following decompressive hinge craniotomy compared to decompressive craniectomy-a human cadaver study

OBJECTIVE

Decompressive hinge craniotomy (DHC) is an alternative treatment option to decompressive craniectomy (DC) for elevated intracranial pressure (ICP). The aim of this study was to characterize the difference in pressure-volume relationship between DHC and DC.

METHODS

We compared the intracranial pressure-volume relationship in a human cadaver model following either DHC, DC, or fixing of the bone plate by titanium clamps. We inserted an intracranial expandable device in two human cadaver specimens, performed either DHC, DC, or bone plate fixation, and gradually increased the intracranial volume while measuring ICP. Following DHC, we also performed CT-scans at pre-defined intervals.

RESULTS

Before ICP exceeded a threshold of 20 mmHg, a fixed bone plate tolerated an increase of 130 ml of intracranial volume, while DHC and DC allowed an increase of 190 ml and 290 ml, respectively. CT-derived calculations following DHC determined that the increase in intracranial volume at ICP 22 mmHg was 65 ml, the maximal increase of intracranial volume was 84 ml, the maximal bone displacement was 21 mm, and the bone plate volume to be 82 ml. Manual stress test of the hinged bone plate did not allow misalignment or intracranial displacement of the bone plate.

CONCLUSION

DHC increases the intracranial volume by up to 84 ml and allows for approximately 60 ml increase of intracranial volume before ICP exceeds 20 mmHg. This indicates, when comparing with results from previous studies of herniation volumes, that DHC will be sufficient in many patients with head injury or cerebral infarction with treatment refractory intracranial hypertension.

Assessment of a Non-Invasive Brain Pulse Monitor to Measure Intra-Cranial Pressure Following Acute Brain Injury

Background

Intracranial pressure (ICP) monitoring requires placing a hole in the skull through which an invasive pressure monitor is inserted into the brain. This approach has risks for the patient and is expensive. We have developed a non-invasive brain pulse monitor that uses red light to detect a photoplethysmographic (PPG) signal arising from the blood vessels on the brain's cortical surface. The brain PPG and the invasive ICP waveform share morphological features which may allow measurement of the intracranial pressure.

Methods

We enrolled critically ill patients with an acute brain injury with invasive ICP monitoring to assess the new monitor. A total of 24 simultaneous invasive ICP and brain pulse monitor PPG measurements were undertaken in 12 patients over a range of ICP levels.

Results

The waveform morphologies were similar for the invasive ICP and brain pulse monitor PPG approach. Both methods demonstrated a progressive increase in the amplitude of P2 relative to P1 with increasing ICP levels. An automated algorithm was developed to assess the PPG morphological features in relation to the ICP level. A correlation was demonstrated between the brain pulse waveform morphology and ICP levels, R²=0.66, P < 0.001.

Conclusion

The brain pulse monitor's PPG waveform demonstrated morphological features were similar to the invasive ICP waveform over a range of ICP levels, these features may provide a method to measure ICP levels.

Trial Registration

ACTRN12620000828921.

Noninvasive intracranial pressure waveforms for estimation of intracranial hypertension and outcome prediction in acute brain-injured patients

Analysis of intracranial pressure waveforms (ICPW) provides information on intracranial compliance. We aimed to assess the correlation between noninvasive ICPW (NICPW) and invasively measured intracranial pressure (ICP) and to assess the NICPW prognostic value in this population. In this cohort, acute brain-injured (ABI) patients were included within 5 days from admission in six Intensive Care Units. Mean ICP (mICP) values and the P2/P1 ratio derived from NICPW were analyzed and correlated with outcome, which was defined as: (a) early death (ED); survivors on spontaneous breathing (SB) or survivors on mechanical ventilation (MV) at 7 days from inclusion. Intracranial hypertension (IHT) was defined by ICP > 20 mmHg. A total of 72 patients were included (mean age 39, 68% TBI). mICP and P2/P1 values were significantly correlated (r = 0.49, p < 0.001). P2/P1 ratio was significantly higher in patients with IHT and had an area under the receiving operator curve (AUROC) to predict IHT of 0.88 (95% CI 0.78–0.98). mICP and P2/P1 ratio was also significantly higher for ED group (n = 10) than the other groups. The AUROC of P2/P1 to predict ED was 0.71 [95% CI 0.53–0.87], and the threshold P2/P1 > 1.2 showed a sensitivity of 60% [95% CI 31–83%] and a specificity of 69% [95% CI 57–79%]. Similar results were observed when decompressive craniectomy patients were excluded. In this study, P2/P1 derived from noninvasive ICPW assessment was well correlated with IHT. This information seems to be as associated with ABI patients outcomes as ICP.

Trial registration: NCT03144219, Registered 01 May 2017 Retrospectively registered, https://www.clinicaltrials.gov/ct2/show/NCT03144219.

A Novel Noninvasive Technique for Intracranial Pressure Waveform Monitoring in Critical Care

BACKGROUND

We validated a new noninvasive tool (B4C) to assess intracranial pressure waveform (ICPW) morphology in a set of neurocritical patients, correlating the data with ICPW obtained from invasive catheter monitoring.

MATERIALS AND METHODS

Patients undergoing invasive intracranial pressure (ICP) monitoring were consecutively evaluated using the B4C sensor. Ultrasound-guided manual internal jugular vein (IJV) compression was performed to elevate ICP from the baseline. ICP values, amplitudes, and time intervals (P2/P1 ratio and time-to-peak [TTP]) between the ICP and B4C waveform peaks were analyzed.

RESULTS

Among 41 patients, the main causes for ICP monitoring included traumatic brain injury, subarachnoid hemorrhage, and stroke. Bland-Altman's plot indicated agreement between the ICPW parameters obtained using both techniques. The strongest Pearson's correlation for P2/P1 and TTP was observed among patients with no cranial damage (r = 0.72 and 0.85, respectively) to the detriment of those who have undergone craniotomies or craniectomies. P2/P1 values of 1 were equivalent between the two techniques (area under the receiver operator curve [AUROC], 0.9) whereas B4C cut-off 1.2 was predictive of intracranial hypertension (AUROC 0.9, p < 000.1 for ICP > 20 mmHg).

CONCLUSION

B4C provided biometric amplitude ratios correlated with ICPW variation morphology and is useful for noninvasive critical care monitoring.