Transient intracranial pressure elevations (B waves) are associated with sleep apnea.

BACKGROUND: Repetitive transient intracranial pressure waveform elevations up to 50 mmHg (ICP B-waves) are often used to define pathological conditions and determine indications for ICP-reducing treatment. We recently showed that nocturnal transient ICP elevations are present in patients without structural brain lesions or hydrocephalus in whom they are associated with sleep apnea. However, whether this signifies a general association between ICP macropatterns and sleep apnea remains unknown. METHODS: We included 34 patients with hydrocephalus, or idiopathic intracranial hypertension (IIH), who were referred to the Neurosurgical Department, Copenhagen, Denmark, from 2017 to 2021. Every patient underwent diagnostic overnight ICP monitoring for clinical indications, with simultaneous polysomnography (PSG) sleep studies. All transient ICP elevations were objectively quantified in all patients. Three patients were monitored with continuous positive airway pressure (CPAP) treatment for an additional night. RESULTS: All patients had transient ICP elevations associated with sleep apnea. The mean temporal delay from sleep apnea to transient ICP elevations for all patients was 3.6 s (SEM 0.2 s). Ramp-type transient ICP elevations with a large increase in ICP were associated with rapid eye movement (REM) sleep and sinusoidal-type elevations with non-REM (NREM) sleep. In three patients treated with CPAP, the treatment reduced the number of transient ICP elevations with a mean of 37%. CPAP treatment resulted in insignificant changes in the average ICP in two patients but elevated the average ICP during sleep in one patient by 5.6 mmHg. CONCLUSION: The findings suggest that sleep apnea causes a significant proportion of transient ICP elevations, such as B-waves, and sleep apnea should be considered in ICP evaluation. Treatment of sleep apnea with CPAP can reduce the occurrence of transient ICP elevations. More research is needed on the impact of slow oscillating mechanisms on transient ICP elevations during high ICP and REM sleep.

k-Shape clustering for extracting macro-patterns in intracranial pressure signals.

BACKGROUND: Intracranial pressure (ICP) monitoring is a core component of neurosurgical diagnostics. With the introduction of telemetric monitoring devices in the last years, ICP monitoring has become feasible in a broader clinical setting including monitoring during full mobilization and at home, where a greater diversity of ICP waveforms are present. The need for identification of these variations, the so-called macro-patterns lasting seconds to minutes-emerges as a potential tool for better understanding the physiological underpinnings of patient symptoms. METHODS: We introduce a new methodology that serves as a foundation for future automatic macro-pattern identification in the ICP signal to comprehensively understand the appearance and distribution of these macro-patterns in the ICP signal and their clinical significance. Specifically, we describe an algorithm based on k-Shape clustering to build a standard library of such macro-patterns. RESULTS: In total, seven macro-patterns were extracted from the ICP signals. This macro-pattern library may be used as a basis for the classification of new ICP variation distributions based on clinical disease entities. CONCLUSIONS: We provide the starting point for future researchers to use a computational approach to characterize ICP recordings from a wide cohort of disorders.

Empirical Mode Decomposition-Based Method for Artefact Removal in Raw Intracranial Pressure Signals.

Intracranial pressure (ICP) signals are often contaminated by artefacts and segments of missing values. Some of these artefacts can be observed as very high and short spikes with a physiologically impossible high slope. The presence of these spikes reduces the accuracy of pattern recognition techniques. Thus, we propose a modified empirical mode decomposition (EMD) method for spike removal in raw ICP signals. The EMD breaks down the signal into 16 intrinsic mode functions (IMFs), combines the first 4 to localize spikes using adaptive thresholding, and then either removes or imputes the identified ICP spikes.

Physical Model for Investigating Intracranial Pressure with Clinical Pressure Sensors and Diagnostic Ultrasound: Preliminary Results.

INTRODUCTION: Intracranial pressure (ICP) is a commonly collected neurocritical parameter, but accurate signal modelling remains challenging. The goal of this project was to mimic clinical ICP waveforms using a physical model. MATERIALS AND METHODS: A physical head model was developed. The skull was segmented from a head computed tomography (CT) scan, remodelled, 3D-printed, and filled with a brain tissue mimicking material and a pressure generator. Pressure measurements and tissue displacement around an attached pressure sensor were explored. RESULTS: Analysis of the measured pressure demonstrated that the waveform did not perfectly resemble that of the clinical ICP. Through iterative improvements and using a revised second pressure generator, subpeaks could be seen in the waveform. A speckle image recorded using ultrasound during pressure application enabled visualization of tissue displacement around the pressure sensor. Comparison with measured ICP signals revealed that minuscule patterns were not distinct in the displacement images. DISCUSSION: We present the first steps towards mimicking clinical ICP using a physical head phantom model. The physical model enabled pressure tests and visualization of tissue displacement and will be foundational for further improvements.

Lumbar puncture position influences intracranial pressure.

BACKGROUND: The standard lumbar puncture position involves maximum flexion of both lumbar and cervical spine. The cerebrospinal fluid opening pressure (CSFop) is measured in a horizontal position. This study investigated if flexion of hip and neck both separately and simultaneously influence intracranial pressure (ICP) to a clinically relevant extent. METHODS: Thirty-nine patients, undergoing invasive ICP monitoring as part of diagnostic work-up, were included. The patients underwent either a vertical postural examination (n = 24) or a horizontal postural examination (n = 15) to examine a varying degree of spine flexion. RESULTS: The vertical examination showed that ICP decreased by 15.2 mmHg when straightening the neck in a sitting lumbar puncture position (n = 24, IQR - 20.1 to - 9.7). In the horizontal examination, ICP increased in all but one patient when changing from supine position to lateral recumbent position (n = 15, median increase of 6.9 mmHg, IQR 3.1 to 9.9). Straightening the hips alone decreased ICP with 0.2 mmHg (n = 15, IQR - 0.5 to 2.0), while straightening the neck alone decreased ICP by 4.0 mmHg (n = 15, IQR - 5.9 to - 1.7). However, when straightening the hip and neck simultaneously ICP decreased by 6.4 mmHg (n = 6, IQR - 9.5 to - 4.4). CONCLUSIONS: Neck flexion alone, and neck flexion and hip flexion in combination, has significant confounding influence on ICP. This may cause patients to shift from a normal ICP range to a pathological ICP range, which will potentially affect treatment decisions. Consensus on guidelines for body position including neck and hip flexion measuring CSFop may be needed.

Long-Term Effect of Decompressive Craniectomy on Intracranial Pressure and Possible Implications for Intracranial Fluid Movements.

BACKGROUND: Decompressive craniectomy (DC) is used in cases of severe intracranial hypertension or impending intracranial herniation. DC effectively lowers intracranial pressure (ICP) but carries a risk of severe complications related to abnormal ICP and/or cerebrospinal fluid (CSF) circulation, eg, hygroma formation, hydrocephalus, and "syndrome of the trephined." OBJECTIVE: To study the long-term effect of DC on ICP, postural ICP regulation, and intracranial pulse wave amplitude (PWA). METHODS: Prospective observational study including patients undergoing DC during a 12-mo period. Telemetric ICP sensors (Neurovent-P-tel; Raumedic, Helmbrechts, Germany) were implanted in all patients. Following discharge from the neuro intensive care unit (NICU), scheduled weekly ICP monitoring sessions were performed during the rehabilitation phase. RESULTS: A total of 16 patients (traumatic brain injury: 7, stroke: 9) were included (median age: 55 yr, range: 19-71 yr). Median time from NICU discharge to cranioplasty was 48 d (range: 16-98 d) and during this period, mean ICP gradually decreased from 7.8 ± 2.0 mm Hg to -1.8 ± 3.3 mm Hg (P = .02). The most pronounced decrease occurred during the first month. Normal postural ICP change was abolished after DC for the entire follow-up period, ie, there was no difference between ICP in supine and sitting position (P = .67). PWA was markedly reduced and decreased from initially 1.2 ± 0.7 mm Hg to 0.4 ± 0.3 mm Hg (P = .05). CONCLUSION: Following NICU discharge, ICP decreases to negative values within 4 wk, normal postural ICP regulation is lost and intracranial PWA is diminished significantly. These abnormalities might have implications for intracranial fluid movements (eg, CSF and/or glymphatic flow) following DC and warrants further investigations.

B waves: a systematic review of terminology, characteristics, and analysis methods.

BACKGROUND: Although B waves were introduced as a concept in the analysis of intracranial pressure (ICP) recordings nearly 60 years ago, there is still a lack consensus on precise definitions, terminology, amplitude, frequency or origin. Several competing terms exist, addressing either their probable physiological origin or their physical characteristics. To better understand B wave characteristics and ease their detection, a literature review was carried out. METHODS: A systematic review protocol including search strategy and eligibility criteria was prepared in advance. A literature search was carried out using PubMed/MEDLINE, with the following search terms: B waves + review filter, slow waves + review filter, ICP B waves, slow ICP waves, slow vasogenic waves, Lundberg B waves, MOCAIP. RESULTS: In total, 19 different terms were found, B waves being the most common. These terminologies appear to be interchangeable and seem to be used indiscriminately, with some papers using more than five different terms. Definitions and etiologies are still unclear, which makes systematic and standardized detection difficult. CONCLUSIONS: Two future lines of action are available for automating macro-pattern identification in ICP signals: achieving strict agreement on morphological characteristics of "traditional" B waveforms, or starting a new with a fresh computerized approach for recognition of new clinically relevant patterns.

Intracranial pressure before and after cranioplasty: insights into intracranial physiology.

OBJECTIVE: Decompressive craniectomy (DC) is an emergency neurosurgical procedure used in cases of severe intracranial hypertension or impending intracranial herniation. The procedure is often lifesaving, but it exposes the brain to atmospheric pressure in the subsequent rehabilitation period, which changes intracranial physiology and probably leads to complications such as hydrocephalus, hygromas, and "syndrome of the trephined." The objective of the study was to study the effect of cranioplasty on intracranial pressure (ICP), postural ICP changes, and intracranial pulse wave amplitude (PWA). METHODS: The authors performed a prospective observational study including patients who underwent DC during a 12-month period. Telemetric ICP sensors were implanted in all patients at the time of DC. ICP was evaluated before and after cranioplasty during weekly measurement sessions including a standardized postural change program. RESULTS: Twelve of the 17 patients enrolled in the study had cranioplasty performed and were included in the present investigation. Their mean ICP in the supine position increased from -0.5 ± 4.8 mm Hg the week before cranioplasty to 6.3 ± 2.5 mm Hg the week after cranioplasty (p < 0.0001), whereas the mean ICP in the sitting position was unchanged (-1.2 ± 4.8 vs -1.1 ± 3.6 mm Hg, p = 0.90). The difference in ICP between the supine and sitting positions was minimal before cranioplasty (1.1 ± 1.8 mm Hg) and increased to 7.4 ± 3.6 mm Hg in the week following cranioplasty (p < 0.0001). During the succeeding 2 weeks of the follow-up period, the mean ICP in the supine and sitting positions decreased in parallel to, respectively, 4.6 ± 3.0 mm Hg (p = 0.0003) and -3.9 ± 2.7 mm Hg (p = 0.040), meaning that the postural ICP difference remained constant at around 8 mm Hg. The mean intracranial PWA increased from 0.7 ± 0.7 mm Hg to 2.9 ± 0.8 mm Hg after cranioplasty (p < 0.0001) and remained around 3 mm Hg throughout the following weeks. CONCLUSIONS: Cranioplasty restores normal intracranial physiology regarding postural ICP changes and intracranial PWA. These findings complement those of previous investigations on cerebral blood flow and cerebral metabolism in patients after decompressive craniectomy.

Feasibility of Telemetric Intracranial Pressure Monitoring in the Neuro Intensive Care Unit.

Intracranial pressure (ICP) monitoring is crucial in the management of acute neurosurgical conditions such as traumatic brain injury (TBI). However, pathological ICP may persist beyond the admission to the neuro intensive care unit (NICU). We investigated the feasibility of telemetric ICP monitoring in the NICU, as this technology provides the possibility of long-term ICP assessment beyond NICU discharge. In this prospective investigation, we implanted telemetric ICP sensors (Raumedic Neurovent-P-tel) instead of conventional, cabled ICP sensors in patients undergoing decompressive craniectomy. We recorded ICP curves, duration of ICP monitoring, signal quality, and complications. Seventeen patients were included (median age 55 years) and diagnoses were: severe TBI (8), malignant middle cerebral artery infarction (8), and spontaneous intracerebral hemorrhage (1). In total, 3015 h of ICP monitoring were performed, and the median duration of ICP monitoring was 188 h (interquartile range [IQR] 54-259). The ICP signal was lost 613 times (displacement of the reader unit on the skin) for a median of 1.5 min, corresponding to 0.8% of the total monitoring period. When the signal was lost, it could always be restored by realignment of the reader unit on the skin above the telemetric sensor. Sixteen of 17 patients survived the NICU admission, and ICP gradually decreased from 10.7 mm Hg (IQR 7.5-13.6) during the first postoperative day to 6.3 mm Hg (IQR 4.0-8.3) after 1 week in the NICU. All 17 implanted telemetric sensors functioned throughout the NICU admission, and no wound infections were observed. Therefore, telemetric ICP monitoring in an acute neurosurgical setting is feasible. Signal quality and stability are sufficient for clinical decision making based on mean ICP. The low sampling frequency (5 Hz) does not permit analysis of intracranial pulse wave morphology, but resolution is sufficient for calculation of derived indices such as the pressure reactivity index (PRx).

Further Controversies About Brain Tissue Oxygenation Pressure-Reactivity After Traumatic Brain Injury.

BACKGROUND: Continuous monitoring of cerebral autoregulation is considered clinically useful due to its ability to warn against brain ischemic insults, which may translate to a relationship with adverse outcome. It is typically performed using the pressure reactivity index (PRx) based on mean arterial pressure and intracranial pressure. A new ORx index based on brain tissue oxygenation and cerebral perfusion pressure (CPP) has been proposed that similarly allows for evaluation of cerebrovascular reactivity. Conflicting results exist concerning its clinical utility. METHODS: Retrospective analysis was performed in 85 patients with traumatic brain injury (TBI). ORx was calculated using three time windows of 5, 20, and 60 min. Correlation coefficients and individual "optimal CPP" (CPPopt) were calculated using both PRx and ORx, and relation to patient outcome investigated. RESULTS: Correlation coefficients for all comparisons between PRx and ORx indicated poor association between these indices (range from -0.04 to 0.07). PRx was significantly lower in patients with good outcome (p = 0.01), while none of the ORx indices proved to be significantly different in the two outcome groups. Higher mortality related to average CPP < CPPopt was found regardless of which index was used to calculate CPPopt. CONCLUSION: In the TBI setting, ORx does not appear to correlate with vascular pressure reactivity as assessed with PRx. Its potential use for individualizing CPP thresholds remains unclear.

The Relationship Between Intracranial Pressure and Age-Chasing Age-Related Reference Values.

BACKGROUND: No true reference values for intracranial pressure (ICP) in humans exist; current values are estimated from measurements in adults who undergo treatment in order to correct ICP. We report ICP values in a "pseudonormal" group of children and adults to examine if age affects ICP. METHODS: We analyzed data from all nonshunted patients undergoing a 24-hour ICP monitoring as part of a diagnostic work-up and included patients with no subsequent suspicion of increased ICP and no need for pressure-relieving treatment with a minimum follow-up period of 3 years. RESULTS: From February 2008 to November 2014, a 24-hour ICP monitoring was performed in 221 patients. Of these patients, 35 (14 children, 21 adults) met the inclusion criteria. Follow-up time to confirm absence of ICP-related disease was 3-9 years. Daytime ICP was 2.8 mmHg ± 2.2 in children and 1.9 mmHg ± 4.2 in adults (P = 0.39). Of 35 patients, 32 had higher nighttime ICP. The difference between daytime and nighttime ICP was similar in children (ΔICP = 5.8 mmHg ± 4.0, P < 0.0001) and adults (ΔICP = 6.1 mm Hg ± 3.3, P < 0.0001). ICP could be described as a decreasing function of age, with an ICP decrement of 0.69 mmHg per decade (P = 0.015). CONCLUSIONS: We found similar differences in daytime and nighttime ICP between children and adults with no ICP-related disease. ICP seems to decrease with age across all ages. This has implications for therapeutic interventions (e.g., shunt valve selection or resistance in external ventricular drainage).

Evaluation of Intracranial Pressure in Different Body Postures and Disease Entities.

We currently do not have sufficient knowledge regarding appropriate boundaries between "normal" and "abnormal" intracranial pressure (ICP) in humans. Our objective in this study was to quantify the effects of postural changes on ICP in normal and ill subjects. As a model for normal patients, we included adult patients scheduled for complete removal of a solitary, clearly demarcated, small brain tumor and performed long-term ICP monitoring using a telemetric device. The ill subjects included required invasive ICP monitoring as part of their diagnostic workup or monitoring of the effect of shunt treatment at our department. All patients were included prospectively for a session of monitored changes in body posture. In our preliminary results from 19 patients, we were able to statistically distinguish between patient groups and assumed body postures, highlighting the need for the further characterization of the effects of postural changes on ICP to inform diagnostic and therapeutic decisions.

Intra-arterial nimodipine for cerebral vasospasm after subarachnoid haemorrhage: Influence on clinical course and predictors of clinical outcome.

Intra-arterial nimodipine (IAN) has shown a promising effect on cerebral vasospasm (CV) after aneurysmal subarachnoid haemorrhage. At our institution, Rigshospitalet, IAN treatment has been used since 2009, but the short- and long-term clinical efficacy of IAN has not yet been assessed. The purpose was to evaluate the efficacy and clinical outcome of IAN treatment of symptomatic CV, and to assess the predictors of clinical outcome. Medical records of 25 patients undergoing a total of 41 IAN treatment sessions were retrospectively reviewed. Data on angiographic results, blood-flow velocities and the clinical condition before and after the IAN treatment were recorded. Predictors of the clinical outcome were assessed with a linear regression model. Positive angiographic response was achieved in 95.1% of 41 IAN treatment sessions. Flow-velocity measurements showed no relationship with angiographic responses of IAN. The immediate clinical improvement was observed in three patients (12%). Five patients (20%) had a favourable outcome at discharge and at three-month follow-up; 10 patients (40%) had a moderate to poor outcome; and the rest (40%) died. Increased number of affected vessels and number of procedures carried out per patient, and a trend toward an increased delay time from symptomatic CV to confirming angiographic CV and thus instituting IAN treatment predicted the poor clinical outcome. IAN treatment appears to be effective in reversing angiographic CV. However, it is not always effective in reversing clinical deterioration, as several other factors including treatment delay affect the clinical course.

Valved or valveless ventriculoperitoneal shunting in the treatment of post-haemorrhagic hydrocephalus: a population-based consecutive cohort study.

BACKGROUND: Implant infection and obstruction are major complications for ventriculoperitoneal shunts in patients with post-haemorrhagic hydrocephalus. In an effort to (1) reduce the incidence of these complications, (2) reduce the rate of shunt failure and (3) shorten the duration of neurosurgical hospitalisation, we have implemented valveless ventriculoperitoneal shunts at our department for adult patients with post-haemorrhagic hydrocephalus and haemorrhagic cerebrospinal fluid at the time of shunt insertion. METHODS: All adult patients (>18 years old) treated for post-haemorrhagic hydrocephalus with ventriculoperitoneal shunting at our institution from 1 January 2008 to 31 December 2014 were included in this retrospective population-based consecutive cohort study. Data were collected by retrospectively reviewing medical records. We compared two different shunt modalities (valveless vs valve-regulated), analysing frequencies of complications, shunt survival and duration of neurosurgical hospitalisation. RESULTS: A total of 214 patients aged 22-86 (mean age, 60.5 ± 11.5 years) were included, comprising 137 valveless and 77 valve-regulated shunts. We found no difference in the rate of surgical shunt revision (p = 0.65) or differences in time interval from insertion to first surgical revision (p = 0.31) between the two shunt modalities. The duration of neurosurgical hospitalisation was shorter for patients receiving a valveless shunt (p = 0.004). Patients with valveless shunts had a lower rate of shunt infection (5.1 % vs 14.3 %, p = 0.02), but a higher rate of overdrainage (10.3 % vs 2.6 %, p = 0.04). CONCLUSION: The use of a valveless shunting for patients with post-haemorrhagic hydrocephalus results in shorter duration of neurosurgical hospitalisation and lower rate of shunt infection, although these advantages should be held up against the risk of overdrainage. We propose valveless shunting to be used as first-line shunting strategy in this patient category, with careful follow-up ensuring that these are substituted by a valve-bearing system if necessary.

Effect of postural changes on ICP in healthy and ill subjects.

BACKGROUND: Reference values and physiological measurements of intracranial pressure (ICP) are primarily reported in the supine position, while reports of ICP in the vertical position are surprisingly rare considering that humans maintain the vertical position for the majority of the day. In order to distinguish normal human physiology from disease entities such as idiopathic intracranial hypertension and normal pressure hydrocephalus, we investigated ICP in different body postures in both normal and ill subjects. METHODS: Thirty-one patients were included: four normal patients following complete removal of a solitary clearly demarcated small brain tumour and fitted with a telemetric ICP monitoring device for long-term ICP monitoring; 27 patients requiring invasive ICP monitoring as a part of their diagnostic work-up or monitoring of shunt treatment effect. ICP was recorded in the following body positions: upright standing, sitting in a chair, supine and right lateral lumbar puncture position. RESULTS: Linear regression of median ICP based on patient posture, group, and purpose of monitoring presented a significant model (p < 0.001), but could not distinguish between patient groups (p = 0.88). Regression of differences in median ICP between body postures and supine ICP as the baseline, presented a highly significant model (p < 0.001) and adjusted R (2) = 0.86. Both body posture (p < 0.001) and patient group (p < 0.001) were highly significant factors. CONCLUSIONS: Differences in ICP between body postures enabled us to distinguish the normal group from patient groups. Normal patients appear able to more tightly regulate ICP when switching body postures.

Evaluation of pre-hospital transport time of stroke patients to thrombolytic treatment.

BACKGROUND: Effective treatment of stroke is time dependent. Pre-hospital management is an important link in reducing the time from occurrence of stroke symptoms to effective treatment. The aim of this study was to evaluate time used by emergency medical services (EMS) for stroke patients during a five-year period in order to identify potential delays and evaluate the reorganization of EMS in Copenhagen in 2009. METHODS: We performed a retrospective analysis of ambulance records from stroke patients suitable for thrombolysis from 1 January 2006 to 7 July 2011. We noted response time from dispatch of the ambulance to arrival at the scene, on-scene time and transport time to the hospital-in total, alarm-to-door time. In addition, we noted baseline characteristics. RESULTS: We reviewed 481 records (58% male, median age 66 years). The median (IQR) alarm-to-door time in minutes was 41 (33-52), of which 18 (12-24) minutes were spent on scene. Response time was reduced from the period before to the period after reorganization (7 vs. 5 minutes, p <0.001). In a linear multiple regression model, higher patient age and longer distance to the hospital correlated with significantly longer transportation time (p <0.001). CONCLUSIONS: This study shows an unchanged alarm-to-door time of 41 minutes over a five-year period. Response time, but not total alarm-to-door time, was reduced during the five years. On-scene time constituted nearly half of the total alarm-to-door time and is thus a point of focus for improvement.

Subacute bacterial endocarditis and subsequent shunt nephritis from ventriculoatrial shunting 14†years after shunt implantation.

Fourteen years after shunt implantation, a 26-year-old patient with myelomeningocele, concomitant hydrocephalus and a ventriculoatrial cerebrospinal fluid (CSF) shunt presented with brief but recurrent episodes of fever predominantly when taking showers or during physical exertion. After 4 years of inconclusive multidisciplinary investigations, the patient progressed into end-stage renal disease before an echocardiogram revealed a vegetative plaque on the tendinous chords of the tricuspid valve. CSF cultures were grown from the shunt valve, confirming bacterial growth of Propionibacterium acnes suspected of causing subacute bacterial endocarditis and subsequent shunt nephritis. The patient was successfully treated with antibiotics combined with ventriculoatrial shunt removal and endoscopic third ventriculocisternostomy (VCS). This case illustrates the nowadays rare, but potentially severe complication of subacute bacterial endocarditis and shunt nephritis. It also exemplifies the VCS as an alternative to implanting foreign shunt systems for CSF diversion.

Intracranial pressure following complete removal of a small demarcated brain tumor: a model for normal intracranial pressure in humans.

OBJECTIVES: Current published normal values for intracranial pressure (ICP) are extrapolated from lumbar CSF pressure measurements and ICP measurements in patients treated for CSF pressure disorders. There is an emerging agreement that true normal ICP values are needed for diagnostic and therapeutic purposes. This study documents normal ICP in humans. METHODS: In this study the authors included adult patients scheduled for complete removal of a solitary, clearly demarcated, small brain tumor. The mean age of these patients was 67 years old (range 58-85 years old). Exclusion criteria were intended to create a study population with as normal brains as possible. A new telemetric ICP monitoring device was implanted at the end of surgery and monitoring was conducted 2 and 4 weeks postoperatively. RESULTS: In the supine position, mean ICP was 0.5 ± 4.0 mm Hg at 4 weeks postoperatively. Postural change to the standing position resulted in a decrease in mean ICP to -3.7 ± 3.8 mm Hg. These results show ICP to be considerably lower than previously estimated. CONCLUSIONS: This study provides a preliminary reference range for normal ICP in humans. It is the first study to show that ICP in the healthy human brain decreases to negative values when assuming the upright position. If these results are later confirmed in a larger series, they might provide reference values for diagnosis and treatment in patients with CSF-related disorders. New normal values also have implications for future shunt design and the ICP target range in hydrocephalus treatment.

Clinical experience with telemetric intracranial pressure monitoring in a Danish neurosurgical center.

BACKGROUND: Monitoring of intracranial pressure (ICP) is important in the optimal treatment of various neurological and neurosurgical diseases. Telemetric ICP monitoring allows long-term measurements in the patient's everyday life and the possibility to perform additional measurements without the procedure related risks of repeated transducer insertions. MATERIALS AND METHODS: We identified all patients in our clinic with an implanted Raumedic(®) telemetric ICP probe (NEUROVENT(®)-P-tel). For each patient we identified diagnosis, indication for implantation, surgical complications, duration of ICP reading, number of ICP recording sessions (in relation to symptoms of increased ICP) and their clinical consequence. RESULTS: We included 21 patients in the evaluation (11 female and 10 male). Median age was 28 (2-83) years and median duration of disease was 11 (0-30) years. Eleven patients had various kinds of hydrocephalus, seven patients had idiopathic intracranial hypertension (IIH) and three patients had normal pressure hydrocephalus (NPH). Fifteen patients had a shunt prior to implantation. Median duration of implantation was 248 (49-666) days and median duration from implantation to last recording session was 154 (8-433) days. In total, 86 recording sessions were performed; 29 resulted in surgical shunt revision, 30 in change of acetazolamide dose or programmable valve setting, 20 required no action and 5 resulted in a new recording session. No surgical complications occurred, except for late wound infection at the surgical site in two patients. CONCLUSION: Telemetric ICP monitoring is useful in patients with complicated CSF dynamic disturbances who would otherwise require repeated invasive pressure monitoring. It seems to be a feasible method to guide adjustment of programmable valve settings and to identify patients with chronic or repeated shunt problems.