The effect of baseline pressure errors on an intracranial pressure-derived index: results of a prospective observational study

Utility of intracranial pressure monitoring as a diagnostic tool in pediatric ventriculomegaly

OBJECTIVE

Intracranial pressure (ICP) monitoring is commonly utilized for identifying pathologic ICP in cases of traumatic brain injury; however, its utility in hydrocephalic children has not been elucidated. Although patients with typical (pressure-active) hydrocephalus present with clear signs and/or symptoms and the need for cerebrospinal fluid (CSF) diversion is often clear, others may have arrested or pressure-compensated hydrocephalus with pathologic ICP elevation masked by ambiguous signs or are completely asymptomatic. Without treatment these pathologic ICP elevations may affect neurologic development or crescendo over time leading to neurological decline. The purpose of this study is to investigate the utility of ICP monitoring as a diagnostic tool in this relatively common patient population and identify ventriculomegaly patients with and without pathologic ICP, thus improving accuracy of identifying those with and without surgical needs.

METHODS

36 patients (≤ 17 years old) underwent 41 inpatient ICP recording sessions between 2016 and 2022 and were retrospectively reviewed. This included patients with a history of severe, nonprogressive ventriculomegaly and normal fundoscopic examinations lacking traditional signs and symptoms concerning for elevated ICP. Nighttime pathological plateau waves were defined as sustained elevations of ICP ≥ 2x baseline for a duration of ≥ 5 minutes.

RESULTS

The mean age of patients was 5.5 years old (range 0-17 years old). 46.3% of patients had prior endoscopic third ventriculostomy (ETV), 14.6% had prior ventriculoperitoneal shunt (VPS), and 39% were without prior surgical intervention. Roughly half (51.2%) of patients had congenital ventriculomegaly while other patients had ventriculomegaly due to other pathologies such as germinal matrix hemorrhage/intraventricular hemorrhage (GMH/IVH) (29.3%), stroke (4.9%), cerebral infections/meningitis (2.4%), or unknown etiology (12.2%). The average procedure time was 19.1 ± 10.5 minutes, and mean length of stay was 2.8 ± 0.7 days. Pathologic ICP was demonstrated in 12 cases (29.3%), 4 (33.3%) of which were asymptomatic. Pathologic ICP was found in 7 of 19 (36.8%) in the prior ETV group, 1 of 6 (16.7%) in prior shunt group, and 4 of 16 (25%) in the non-surgical group (p = 0.649). Among those with pathologic ICP, 6 (50%) cases received an ETV, 5 (41.7%) cases underwent VPS placement, and 1 (8.3%) case underwent a VPS revision. There were no infectious complications or cases of hemorrhage. 4 patients required repositioning of the ICP monitor due to dislodgement.

CONCLUSION

Inpatient ICP monitoring is a safe and effective diagnostic tool for evaluating the presence of pathologic ICP in severe, persistent non-progressive ventriculomegaly. The use of ICP monitoring may aid in identifying patients with pressure-compensated hydrocephalus who demonstrate pathologic ICP where surgical intervention may be warranted, while preventing unnecessary CSF diversion in those without pathology.

Relationship between the shape of intracranial pressure pulse waveform and computed tomography characteristics in patients after traumatic brain injury

BACKGROUND

Midline shift and mass lesions may occur with traumatic brain injury (TBI) and are associated with higher mortality and morbidity. The shape of intracranial pressure (ICP) pulse waveform reflects the state of cerebrospinal pressure-volume compensation which may be disturbed by brain injury. We aimed to investigate the link between ICP pulse shape and pathological computed tomography (CT) features.

METHODS

ICP recordings and CT scans from 130 TBI patients from the CENTER-TBI high-resolution sub-study were analyzed retrospectively. Midline shift, lesion volume, Marshall and Rotterdam scores were assessed in the first CT scan after admission and compared with indices derived from the first 24 h of ICP recording: mean ICP, pulse amplitude of ICP (AmpICP) and pulse shape index (PSI). A neural network model was applied to automatically group ICP pulses into four classes ranging from 1 (normal) to 4 (pathological), with PSI calculated as the weighted sum of class numbers. The relationship between each metric and CT measures was assessed using Mann-Whitney U test (groups with midline shift > 5 mm or lesions > 25 cm3 present/absent) and the Spearman correlation coefficient. Performance of ICP-derived metrics in identifying patients with pathological CT findings was assessed using the area under the receiver operating characteristic curve (AUC).

RESULTS

PSI was significantly higher in patients with mass lesions (with lesions: 2.4 [1.9-3.1] vs. 1.8 [1.1-2.3] in those without; p << 0.001) and those with midline shift (2.5 [1.9-3.4] vs. 1.8 [1.2-2.4]; p < 0.001), whereas mean ICP and AmpICP were comparable. PSI was significantly correlated with the extent of midline shift, total lesion volume and the Marshall and Rotterdam scores. PSI showed AUCs > 0.7 in classification of patients as presenting pathological CT features compared to AUCs ≤ 0.6 for mean ICP and AmpICP.

CONCLUSIONS

ICP pulse shape reflects the reduction in cerebrospinal compensatory reserve related to space-occupying lesions despite comparable mean ICP and AmpICP levels. Future validation of PSI is necessary to explore its association with volume imbalance in the intracranial space and a potential complementary role to the existing monitoring strategies.

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.

Intracranial Pressure and Intracranial Elastance Monitoring in Neurocritical Care

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

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

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

Assessing Cerebral Hemodynamic Stability After Brain Injury

OBJECTIVE

Following brain injury, unstable cerebral hemodynamics can be characterized by abnormal rises in intracranial pressure (ICP). This behavior has been quantified by the RAP index: the correlation (R) between ICP pulse amplitude (A) and mean (P). While RAP could be a valuable indicator of autoregulatory processes, its prognostic ability is not well established and its validity has been questioned due to potential errors in measurement. Here, we test (1) whether RAP is a consistent measure of intracranial hemodynamics and (2) whether RAP has prognostic value in predicting hemodynamic instability following brain injury.

MATERIALS AND METHODS

RAP was tested in seven brain injured patients treated in a surgical intensive care unit. A sample of ICP data was randomly chosen and segmented into 1 hour periods. Hours were then categorized as either stable, which contained no sharp rises in ICP, or unstable, which contained ≥1 sharp rise-where a sharp rise is defined as ICP exceeding a mean slope of 0.15 mmHg/s. Equal numbers of stable and unstable segments were then selected for each patient. RAP was calculated as the Pearson's correlation coefficient between ICP pulse amplitude (AMP) and mean (mICP), determined in 6 second windows, according to established methods.

RESULTS

Results showed that (1) average AMP and ICP levels were similar between stable and unstable periods and (2) unstable periods were identified by RAP values exceeding 0.6 with an average positive predictive value of 74%.

CONCLUSIONS

We conclude that RAP can provide a valid measure of ICP dynamics, is not affected by sensor drift, and can better distinguish periods of instability than ICP or AMP alone.

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.

Comparative observational study on the clinical presentation, intracranial volume measurements, and intracranial pressure scores in patients with either Chiari malformation Type I or idiopathic intracranial hypertension

OBJECTIVE Several lines of evidence suggest common pathophysiological mechanisms in Chiari malformation Type I (CMI) and idiopathic intracranial hypertension (IIH). It has been hypothesized that tonsillar ectopy, a typical finding in CMI, is the result of elevated intracranial pressure (ICP) combined with a developmentally small posterior cranial fossa (PCF). To explore this hypothesis, the authors specifically investigated whether ICP is comparable in CMI and IIH and whether intracranial volumes (ICVs) are different in patients with CMI and IIH, which could explain the tonsillar ectopy in CMI. The authors also examined whether the symptom profile is comparable in these 2 patient groups. METHODS The authors identified all CMI and IIH patients who had undergone overnight diagnostic ICP monitoring during the period from 2002 to 2014 and reviewed their clinical records and radiological examinations. Ventricular CSF volume (VV), PCF volume (PCFV), and total ICV were calculated from initial MRI studies by using volumetric software. The static and pulsatile ICP scores during overnight monitoring were analyzed. Furthermore, the authors included a reference (REF) group consisting of patients who had undergone ICP monitoring due to suspected idiopathic normal-pressure hydrocephalus or chronic daily headache and showed normal pressure values. RESULTS Sixty-six patients with CMI and 41 with IIH were identified, with comparable demographics noted in both groups. The occurrence of some symptoms (headache, nausea, and/or vomiting) was comparable between the cohorts. Dizziness and gait ataxia were significantly more common in patients with CMI, whereas visual symptoms, diplopia, and tinnitus were significantly more frequent in patients with IIH. The cranial volume measurements (VV, PCFV, and ICV) of the CMI and IIH patients were similar. Notably, 7.3% of the IIH patients had tonsillar descent qualifying for diagnosis of CMI (that is, > 5 mm). The extent of tonsillar ectopy was significantly different between the CMI and IIH cohorts (p < 0.001) but also between these 2 cohorts and the REF group. Pulsatile ICP was elevated in both cohorts without any significant between-group differences; however, static ICP was significantly higher (p < 0.001) in the IIH group. CONCLUSIONS This study showed comparable and elevated pulsatile ICP, indicative of impaired intracranial compliance, in both CMI and IIH cohorts, while static ICP was higher in the IIH cohort. The data did not support the hypothesis that reduced PCFV combined with increased ICP causes tonsillar ectopy in CMI. Even though impaired intracranial compliance seems to be a common pathophysiological mechanism behind both conditions, the mechanisms explaining the different clinical and radiological presentations of CMI and IIH remain undefined.