Mean Intracranial Pressure Wave Amplitude Research Articles

Preoperative estimation of intracranial compliance in symptomatic children with Chiari malformation type 1: impact on outcome and risk of complications

BackgroundThe role of reduced intracranial compliance (ICC) in the outcome after foramen magnum decompression (FMD) was demonstrated in adults with Chiari malformation Type 1 (CMI). However, similar observations from children treated for CMI are missing.MethodsWe reviewed pediatric cases of CMI referred to FMD between 2006 and 2022. Children with clinical and/or radiological signs suggesting reduced ICC (Group A) underwent overnight measurements of the pulsatile intracranial pressure (ICP): mean ICP wave amplitude (MWA) served as a surrogate marker of ICC. Children with more typical symptoms of CMI (Group B) underwent FMD without preoperative ICC estimation. This study presents the clinical, radiological, and outcome differences between these groups.ResultsSixty-four children (mean age 11.1 ± 4.3 years) underwent FMD: In Group A (n = 30), the finding of reduced ICC as estimated from preoperative ICP measurement resulted in CSF diversion (ventriculoperitoneal shunt) before FMD in 11 children. Two patients required shunt due to complications after FMD (total shunt rate 43%). In Group B (n = 34) treated with FMD without preoperative ICC estimation, five children (15%) required shunting due to complications. In Group A, we found a significantly higher frequency of headache, nausea, fatigue, and dizziness. The outcome assessed by the modified Chicago Chiari Outcome Scale (mean follow-up 83 ± 57 months) was comparable between the groups, but the complication rate after FMD was significantly lower in Group A (7% vs. 32%; p = 0.011). The number of procedures (ICP measurement, FMD, shunt, re-do FMD, shunt revisions) was significantly higher in Group A (2.6 ± 0.9 vs. 1.5 ± 1.1 per patient; p < 0.001).ConclusionIn symptomatic children with CMI, the preoperative estimation of ICC from the overnight measurement of pulsatile ICP was more reliable for identifying those with reduced ICC than clinical and radiological assessment alone. When children with abnormally reduced ICC were identified and treated with CSF diversion before FMD, the complication rate was significantly reduced.

Intracranial Pressure Monitoring for Acute Brain Injured Patients: When, How, What Should We Monitor.

While there is no level I recommendation for intracranial pressure (ICP) monitoring, it is typically indicated for patients with severe traumatic brain injury (TBI) with a Glasgow Coma Scale (GCS) score of 3-8 (class II). Even for moderate TBI patients with GCS 9-12, ICP monitoring should be considered for risk of increased ICP. The impact of ICP monitoring on patient outcomes is still not well-established, but recent studies reported a reduction of early mortality (class III) in TBI patients. There is no standard protocol for the application of ICP monitoring. In cases where cerebrospinal fluid drainage is required, an external ventricular drain is commonly used. In other cases, parenchymal ICP monitoring devices are generally employed. Subdural or non-invasive forms are not suitable for ICP monitoring. The mean value of ICP is the parameter recommended for observation in many guidelines. In TBI, values above 22 mmHg are associated with increased mortality. However, recent studies proposed various parameters including cumulative time with ICP above 20 mmHg (pressure-time dose), pressure reactivity index, ICP waveform characteristics (pulse amplitude of ICP, mean ICP wave amplitude), and the compensatory reserve of the brain (reserve-amplitude-pressure), which are useful in predicting patient outcomes and guiding treatment. Further research is required for validation of these parameters compared to simple ICP monitoring.

Noninvasive Estimation of Pulsatile and Static Intracranial Pressure by Optical Coherence Tomography.

PurposeTo explore the ability of optical coherence tomography (OCT) to noninvasively estimate pulsatile and static intracranial pressure (ICP).MethodsAn OCT examination was performed in patients who underwent continuous overnight monitoring of the pulsatile and static ICP for diagnostic purpose. We included two patient groups, patients with idiopathic intracranial hypertension (IIH; n = 20) and patients with no verified cerebrospinal fluid disturbances (reference; n = 12). Several OCT parameters were acquired using spectral-domain OCT (RS-3000 Advance; NIDEK, Singapore). The ICP measurements were obtained using a parenchymal sensor (Codman ICP MicroSensor; Johnson & Johnson, Raynham, MA, USA). The pulsatile ICP was determined as the mean ICP wave amplitude (MWA), and the static ICP was determined as the mean ICP.ResultsThe peripapillary Bruch's membrane angle (pBA) and the optic nerve head height (ONHH) differed between the IIH and reference groups and correlated with both MWA and mean ICP. Both OCT parameters predicted elevated MWA. Area under the curve and cutoffs were 0.82 (95% confidence interval [CI], 0.66–0.98) and -0.65° (sensitivity/specificity; 0.75/0.92) for pBA and 0.84 (95% CI, 0.70–0.99) and 405 µm (0.88/0.67) for ONHH. Adjusting for age and body mass index resulted in nonsignificant predictive values for mean ICP, whereas the predictive value for MWA remained significant.ConclusionsThis study provides evidence that the OCT parameters pBA and ONHH noninvasively can predict elevated pulsatile ICP, represented by the MWA.Translational RelevanceOCT shows promise as a method for noninvasive estimation of ICP.

Predictive values of parameters of intracranial pressure wave for postoperative global cerebral edema in patients with aneurysmal subarachnoid hemorrhage

Objective To investigate the correlation between the parameters of intracranial pressure (ICP) wave and global cerebral edema for providing basis of early prediction and intervention for global cerebral edema after operation in patients with aneurysmal subarachnoid hemorrhage (aSAH). Methods A total of 80 patients with aSAH admitted to Department of Neurosurgery, the First Affiliated Hospital of Chongqing Medical University from May 2017 to December 2017 were retrospectively enrolled. The parameters of ICP wave and clinical data of 80 patients within 3 days after intracranial aneurysm clipping were collected and analyzed. The aSAH patients were divided into the global cerebral endema (GCE) group (n=13) and NO-GCE group (n=67)to compare the clinical data and parameters of ICP wave. The multivariate logistic regression analysis was used to determine the risk factors that might lead to GCE. According to receiver operating characteristic (ROC) curve, diagnostic threshold values for GCE were evaluated and sensitivity and specificity were calculated for optimal thresholds to investigate the predictive value of parameters of intracranial pressure wave for postoperative GCE. Results The difference of mFisher(modified Fisher) grading, mean ICP wave amplitude (MWA) and R-symbol of correlation between amplitude and pressure (RAP) were significant between NO-GCE group and GCE group (P value: 0.012, 0.005, 0.001, respectively). The result of multivariate logistic regression analysis showed that mFisher grading (OR=8.896, 95%CI: 1.678-47.165, P=0.010), RAP (OR=2.130, 95%CI: 1.155-3.931, P=0.016) were independent risk factors of postoperative GCE. The optimal threshold values of MWA and RAP were 3.853 and 0.480 respectively, which had high diagnostic value in prediction of GCE. The relevant sensitivity and specificity were 84.6% and 70.1% for MWA and 92.3% and 74.6% for RAP. Conclusions The mFisher grading, MWA and RAP might be related to postoperative GCE in patients with aSAH.The mFisher grading and RAP are independent risk factors of postoperative GCE in patients with aSAH. Monitoring of MWA and RAP could help identify the early occurrence of GCE. Key words: Intracranial aneurysm; Subarachnoid hemorrhage; Intracranial pressure; Global cerebral edema; Predictive value

Intracranial volume versus static and pulsatile intracranial pressure values in children with craniosynostosis.

Reduced intracranial volume (ICV) and raised intracranial pressure (ICP) are assumed to be principal pathophysiological mechanisms in childhood craniosynostosis. This study examined the association between ICV and ICP and whether ICV can be used to estimate the ICP. The authors analyzed ICV and ICP measurements from children with craniosynostosis without concurrent hydrocephalus and from age-matched individuals without craniosynostosis who underwent diagnostic ICP measurement. The study included 19 children with craniosynostosis (mean age 2.2 ± 1.9 years) and 12 reference individuals without craniosynostosis (mean age 2.5 ± 1.6 years). There was no difference in ICV between the patient and reference cohorts. Both mean ICP (17.1 ± 5.6 mm Hg) and mean wave amplitude (5.9 ± 2.6 mm Hg) were higher in the patient cohort. The results disclosed no significant association between ICV and ICP values in the patient or reference cohorts, and no association was seen between change in ICV and ICP values after cranial vault expansion surgery (CVES) in 5 children in whom ICV and ICP were measured before and after CVES. In this cohort of children with craniosynostosis, there was no significant association between ICV and ICP values prior to CVES and no significant association between change in ICV and ICP values after CVES in a subset of patients. Therefore, ICV could not reliably estimate the ICP values. The authors suggest that intracranial hypertension in childhood craniosynostosis may not be caused by reduced ICV alone but rather by a distorted relationship between ICV and the volume of intracranial content (brain tissue, CSF, and blood).

Non-invasive Estimation of the Intracranial Pressure Waveform from the Central Arterial Blood Pressure Waveform in Idiopathic Normal Pressure Hydrocephalus Patients

This study explored the hypothesis that the central aortic blood pressure (BP) waveform may be used for non-invasive estimation of the intracranial pressure (ICP) waveform. Simultaneous invasive ICP and radial artery BP waveforms were measured in 29 individuals with idiopathic normal pressure hydrocephalus (iNPH). The central aortic BP waveforms were estimated from the radial artery BP waveforms using the SphygmoCor system. For each individual, a transfer function estimate between the central aortic BP and the invasive ICP waveforms was found (Intra-patient approach). Thereafter, the transfer function estimate that gave the best fit was chosen and applied to the other individuals (Inter-patient approach). To validate the results, ICP waveform parameters were calculated for the estimates and the measured golden standard. For the Intra-patient approach, the mean absolute difference in invasive versus non-invasive mean ICP wave amplitude was 1.9 ± 1.0 mmHg among the 29 individuals. Correspondingly, the Inter-patient approach resulted in a mean absolute difference of 1.6 ± 1.0 mmHg for the 29 individuals. This method gave a fairly good estimate of the wave for about a third of the individuals, but the variability is quite large. This approach is therefore not a reliable method for use in clinical patient management.

The pathophysiology of chronic noncommunicating hydrocephalus: lessons from continuous intracranial pressure monitoring and ventricular infusion testing.

OBJECTIVE The pathophysiology of chronic noncommunicating hydrocephalus (ncHC) is poorly understood. This present study explored whether lessons about the pathophysiology of this clinical entity might be retrieved from results of overnight monitoring of pulsatile and static intracranial pressure (ICP) and ventricular infusion testing. METHODS The study cohort included adult patients (> 20 years of age) with chronic ncHC due to aqueductal stenosis in whom symptoms had lasted a minimum of 6 months. A reference cohort consisted of age- and sex-matched patients managed for communicating HC (cHC). Information about symptoms and clinical improvement following surgery was retrieved from a quality register, and results of overnight ICP recordings and ventricular infusion testing were retrieved from the hospital ICP database. RESULTS The cohort with ncHC consisted of 61 patients of whom 6 (10%) were managed conservatively, 34 (56%) by endoscopic third ventriculostomy (ETV), and 21 (34%) using ETV and subsequent shunt surgery. In patients responding to surgery, pulsatile ICP (mean ICP wave amplitude) was significantly increased to a similar magnitude in patients with ncHC and the reference cohort (cHC). Furthermore, intracranial compliance (ICC) was reduced in clinical responders. The results of ventricular infusion testing provided evidence that patients responding to ETV have impaired ventricular CSF absorption, while those requiring shunt placement after ETV present with impaired CSF absorption both in the intraventricular and extraventricular compartments. CONCLUSIONS The study may provide some lessons about the pathophysiology of chronic ncHC. First, increased pulsatile ICP and impaired ICC characterize patients with chronic ncHC who respond clinically to CSF diversion surgery, even though static ICP is not increased. Second, in patients responding clinically to ETV, impaired ventricular CSF absorption may be a key factor. Patients requiring shunt placement for clinical response appear to have both intraventricular and extraventricular CSF absorption failure. A subgroup of patients with ncHC due to aqueductal stenosis has normal ventricular CSF absorption and normal ICC and may not be in need of surgical CSF diversion.

The association between the pulse pressure gradient at the cranio-cervical junction derived from phase-contrast magnetic resonance imaging and invasively measured pulsatile intracranial pressure in symptomatic patients with Chiari malformation type 1.

In symptomatic Chiari malformation type 1 (CMI), impaired intracranial compliance (ICC) is associated with an increased cranio-spinal pulsatile pressure gradient. Phase-contrast magnetic resonance imaging (MRI) represents a non-invasive modality for the assessment of the pulse pressure gradient at the cranio-cervical junction (CCJ). We wished to explore how the MRI-derived pulse pressure gradient (MRI-dP) compares with invasively measured pulsatile intracranial pressure (ICP) in CMI, and with healthy controls. From phase-contrast MRI of CMI patients and healthy controls, we computed cerebrospinal fluid (CSF) flow velocities and MRI-dP at the CCJ. We assessed bidirectional flow and compared the flow between the anterior and the posterior subarachnoid space at the CCJ. We computed total intracranial volume (ICV), ventricular CSF volume (VV), and posterior cranial fossa volume (PCFV). We analyzed the static and pulsatile ICP scores from overnight monitoring in CMI patients. Five CMI patients and four healthy subjects were included. The CMI group had a significantly larger extent of tonsillar ectopia, smaller PCFV, and a smaller area of CSF in the FM. The pulsatile ICP (mean ICP wave amplitude, MWA) was abnormally increased in 4/5 CMI patients and correlated positively with MRI-dP. However, the MRI-dP as well as the CSF flow velocities did not differ significantly between CMI and healthy subjects. Moreover, bidirectional flow was observed in both CMI as well as healthy subjects, with no significant difference. In symptomatic CMI patients, we found a significant association between the pulse pressure gradient at the CCJ derived from phase-contrast MRI and the pulsatile ICP (MWA) measured invasively. However, the MRI-dP was close to identical in CMI patients and healthy subjects. Moreover, the CSF flow velocities at the CCJ and the occurrence of bidirectional flow were not different in CMI patients and healthy individuals. Further studies are required to determine the diagnostic role of phase-contrast MRI in CMI patients.

Antisecretory factor (AF) exerts no effects on intracranial pressure (ICP) waves and ICP in patients with idiopathic normal pressure hydrocephalus and idiopathic intracranial hypertension

BackgroundAntisecretory factor (AF) and derivates thereof counteract brain edema and inflammation, and normalize ICP dynamics. The aim of the present study was to assess whether AF normalized the abnormal ICP waves, indicative of impaired intracranial compliance, seen in patients with idiopathic normal pressure hydrocephalus (iNPH) and idiopathic intracranial hypertension (IIH). The hypothesis was that brain swelling contributes to the abnormal ICP waves. MethodsThe study enrolled patients undergoing diagnostic ICP wave monitoring for either iNPH or IIH. The ICP waves and ICP were recorded continuously before and after oral administration of Salovum® (0.5g/kg body weight/day divided by three doses), a freeze-dried egg yolk enriched in AF activity. Mean ICP wave amplitude (MWA), mean ICP wave rise time coefficient (MWRTC), and mean ICP were compared before and after Salovum® administration. ResultsA total of 10 iNPH patients and 8 IIH patients were included. No significant changes in the ICP wave indices or ICP were seen after Salovum® administration. Neither any significant time-dependent effect was observed. ConclusionThe lack of effect of Salovum® on ICP wave indices and ICP in iNPH and IIH may provide indirect evidence that brain swelling does not play a crucial role in the ICP wave indices or ICP of these conditions.

A Randomized and Blinded Single-Center Trial Comparing the Effect of Intracranial Pressure and Intracranial Pressure Wave Amplitude-Guided Intensive Care Management on Early Clinical State and 12-Month Outcome in Patients With Aneurysmal Subarachnoid Hemorrhage

In patients with aneurysmal subarachnoid hemorrhage (SAH), preliminary results indicate that the amplitude of the single intracranial pressure (ICP) wave is a better predictor of the early clinical state and 6-month outcome than the mean ICP. To perform a randomized and blinded single-center trial comparing the effect of mean ICP vs mean ICP wave amplitude (MWA)-guided intensive care management on early clinical state and outcome in patients with aneurysmal SAH. Patients were randomized to 2 different types of ICP management: maintenance of mean ICP less than 20 mm Hg and MWA less than 5 mm Hg. Early clinical state was assessed daily using the Glasgow Coma Scale. The primary efficacy variable was 12-month outcome in terms of the Rankin Stroke Score. Ninety-seven patients were included in the study. There were no significant differences in treatment between the 2 groups apart from a larger volume of cerebrospinal fluid drained during week 1 in the MWA group. There was a tendency toward higher Glasgow Coma Scale scores in the MWA group during weeks 1 (P = .08) and 2 (P = .07). Outcome in terms of Rankin Stroke Score at 12 months was significantly better in the MWA group (P < .05). This randomized and blinded trial disclosed a significant better primary efficacy variable (Rankin Stroke Score after 12 months) in the MWA patient group. We suggest that proactive intensive care management with MWA-tailored cerebrospinal fluid drainage during the first week improves aneurysmal SAH outcome.

Static and pulsatile intracranial pressure in idiopathic intracranial hypertension

Objective The aim of this observational study was to characterize the static and pulsatile intracranial pressure (ICP) in conservatively (medically) treated idiopathic intracranial hypertension (IIH) patients in need of shunt surgery, and also in patients with chronic daily headache (CDH) without visual disturbances. Methods The material includes 14 IIH patients and 7 CDH patients in whom ICP was monitored continuously over-night. Static ICP was characterized by mean ICP, pulsatile ICP was characterized by the wave amplitude, rise time, and rise time coefficient. Results In the IIH group all 14 had headache and visual disturbances. Mean ICP was high ( >15 mmHg) in only 7 patients (50%), while mean ICP wave amplitude was high (≥4 mmHg) in all 14 (100%). All IIH patients were shunted and improved clinically thereafter (i.e., relief from visual disturbances and/or headache). None in the CDH group had high mean ICP or mean ICP wave amplitude, and none were shunted. Conclusions In this cohort of 14 conservatively treated IIH patients with lasting and shunt-responsive headache and visual disturbances, the mean ICP wave amplitude was elevated (≥4 mmHg) in all patients despite normal mean ICP (<15 mmHg) in 7 patients (all but one on medication). Therefore, the pulsatile ICP may be more relevant than the static ICP in the diagnostic setting for patients with IIH. Further prospective standardized approaches are warranted.

A dynamic nonlinear relationship between the static and pulsatile components of intracranial pressure in patients with subarachnoid hemorrhage

In the search for optimal monitoring and predictive tools in neurocritical care, the relationship of the pulsatile component of intracranial pressure (ICP) and the pressure itself has long been of great interest. Higher pressure often correlates with a higher pulsatile response to the heartbeat, interpreted as a type of compliance curve. Various mathematical approaches have been used, but regardless of the formula used, it is implicitly assumed that a reproducible curve exists. The authors investigated the stability of the correlation between static and pulsatile ICPs in patients with subarachnoid hemorrhage (SAH) who were observed for several hours by using data sets large enough to allow such calculations to be made. The ICP recordings were obtained in 39 patients with SAH and were parsed into 6-second time windows (1,998,944 windows in 197 recordings). The ICP parameters were computed for each window as follows: static ICP was defined as the mean ICP, and pulsatile ICP was characterized by mean ICP wave amplitude, rise time, and rise time coefficient. The mean ICP and ICP wave amplitudes were simultaneously high or low (the expected correlation) in only approximately 60% of observations. Furthermore, static and pulsatile ICP correlated well only over short intervals; the degree of correlation weakened over periods of hours and was inconsistent across patients and within individual patients over time. Decorrelation originated with abrupt shifting and gradual drifting of mean ICP and ICP wave amplitude over several hours. The relationship between the static and pulsatile components of ICPs changes over time. It evolves, even in individual patients, over a number of hours. This can be one reason the observation of high pulsatile ICP (indicative of reduced intracranial compliance) despite normal mean ICP that is seen in some patients with SAH. The meaning and potential clinical usefulness of such changes in the curves is uncertain, but it implies that clinical events result not only from moving further out on a compliance curve; in practice, the curve, and the biological system that underlies the curve, may itself change.

Cerebrospinal fluid pulse pressure amplitude during lumbar infusion in idiopathic normal pressure hydrocephalus can predict response to shunting

BackgroundWe have previously seen that idiopathic normal pressure hydrocephalus (iNPH) patients having elevated intracranial pressure (ICP) pulse amplitude consistently respond to shunt surgery. In this study we explored how the cerebrospinal fluid pressure (CSFP) pulse amplitude determined during lumbar infusion testing, correlates with ICP pulse amplitude determined during over-night ICP monitoring and with response to shunt surgery. Our goal was to establish a more reliable screening procedure for selecting iNPH patients for shunt surgery using lumbar intrathecal infusion.MethodsThe study population consisted of all iNPH patients undergoing both diagnostic lumbar infusion testing and continuous over-night ICP monitoring during the period 2002-2007. The severity of iNPH was assessed using our NPH grading scale before surgery and 12 months after shunting. The CSFP pulse was characterized from the amplitude of single pressure waves.ResultsTotally 62 iNPH patients were included, 45 of them underwent shunt surgery, in whom 78% were shunt responders. Among the 45 shunted patients, resistance to CSF outflow (Rout) was elevated (≥ 12 mmHg/ml/min) in 44. The ICP pulse amplitude recorded over-night was elevated (i.e. mean ICP wave amplitude ≥ 4 mmHg) in 68% of patients; 92% of these were shunt responders. In those with elevated overnight ICP pulse amplitude, we found also elevated CSFP pulse amplitude recorded during lumbar infusion testing, both during the opening phase following lumbar puncture and during a standardized period of lumbar infusion (15 ml Ringer over 10 min). The clinical response to shunting after 1 year strongly associated with the over-night ICP pulse amplitude, and also with the pulsatile CSFP during the period of lumbar infusion. Elevated CSFP pulse amplitude during lumbar infusion thus predicted shunt response with sensitivity of 88 and specificity of 60 (positive and negative predictive values of 89 and 60, respectively).ConclusionsIn iNPH patients, shunt response can be anticipated in 9/10 patients with elevated overnight ICP pulse amplitude, while in only 1/10 with low ICP pulse amplitude. Additionally, the CSFP pulse amplitude during lumbar infusion testing was elevated in patients with elevated over-night ICP pulse amplitude. In particular, measurement of CSFP pulse amplitude during a standardized infusion of 15 ml Ringer over 10 min was useful in predicting response to shunt surgery and can be used as a screening procedure for selection of iNPH patients for shunting.

Impact of sampling rate for time domain analysis of continuous intracranial pressure (ICP) signals

Time domain analysis of the intracranial pressure (ICP) waveform is critically dependent on the exact reproduction of the ICP waveform. This study explored how the sampling rate of the ICP signal affects the time domain analysis. It was also assessed through this study how upsampling (interpolation) improves the time domain analysis. From the hospital database, a set of 55 ICP waveforms were retrieved from 48 patients (28 children and 20 adults). First, the ICP signals originally sampled at 200 or 100 Hz were compared with the ICP signals downsampled to 5, 10, 20, 25, 50 Hz (and 100 Hz). Second, the original ICP signals were compared with ICP signals upsampled (i.e. interpolated) to 100 Hz (from 5, 10, 20, 25 or 50 Hz). For each ICP recording the output of time domain analysis was the average value and the quantitative distribution of mean ICP wave amplitudes determined every six second (6 s) time window. The total material incorporated a total of 373,371 6 s time windows. Downsampling revealed that the time domain analysis could be most faithfully applied to ICP signals sampled at 50 Hz or above, while ICP signals sampled at 25 Hz deviated more from the original signal than we would accept from a clinical perspective. The use of interpolation gave better representation of the peaks, and should be applied to all ICP signals sampled at lower rate than 100 Hz.

Changes in intracranial pulse pressure amplitudes after shunt implantation and adjustment of shunt valve opening pressure in normal pressure hydrocephalus

We have previously reported that the intracranial pulse pressure amplitudes were elevated in idiopathic normal pressure hydrocephalus (NPH) patients responding to shunt surgery. Whether or not shunt implantation or adjustment of the shunt valve opening pressure modifies the intracranial pulse pressure amplitudes in NPH patients remains to be established. This report summarises our observations. Thirteen patients with NPH (idiopathic in nine and secondary in four) are presented in whom continuous intracranial pressure (ICP) monitoring was done before and after shunt implantation. In two, ICP monitoring was also done during adjustment of shunt valve opening pressure. The mean ICP and mean ICP wave amplitude (i.e. pulse pressure amplitudes) were determined in 6-s time windows. After shunt implantation there was a fall in both mean ICP and mean ICP wave amplitude; the reduction in the two ICP parameters correlated significantly. However, mean ICP in the supine position was normal (i.e. <15 mmHg) in 12 of 13 patients before shunt placement, and remained normal after shunting. According to our criteria, the mean ICP wave amplitudes were elevated before shunting in 12 of 13 patients and became "normalised" the day after shunting in nine patients. The reduction in mean ICP wave amplitude after shunt was highly significant at the group level. Moreover, adjustment of shunt valve opening pressure modified the levels of mean ICP wave amplitudes. The present observations in 13 NPH patients indicate that shunt implantation reduces mean ICP wave amplitudes. Moreover, the level of reduction can be tailored by adjustment of the shunt valve opening pressure.

Rapid and severe rise in static and pulsatile intracranial pressures during a generalized epileptic seizure

In a patient with no prior history of seizures we were able to record static (mean) intracranial pressure (ICP) and pulsatile ICP (mean ICP wave amplitude) continuously during a first-time generalized epileptic seizure. The patient experienced episodic headache five months after a subarachnoid haemorrhage. In order to rule out low-pressure hydrocephalus she was admitted for a 24-hour intracranial pressure registration. ICP parameters were normal prior to the seizure. We observed an immediate and enormous rise in both static (mean) ICP and pulsatile ICP (mean ICP wave amplitude). Mean ICP and ICP wave amplitude peaked at 93 mmHg and 22 mmHg, respectively. Pulsatile ICP remained elevated after normalization of static ICP and may indicate impairment of intracranial compliance even after the static ICP was normalized.

Association among intracranial compliance, intracranial pulse pressure amplitude and intracranial pressure in patients with intracranial bleeds

Objective: To investigate the association among intracranial compliance (ICC), intracranial pulse pressure amplitude and intracranial pressure (ICP) in patients with intracranial bleeds.Methods: Five patients with intracranial bleeds had their ICC and ICP monitored during days 1–8 after ictus. The recordings were stored as raw data files and analysed retrospectively. The parameters mean ICC, mean ICP wave amplitude and mean ICP were determined and average values were calculated in 1 hour time periods.Results: A total of 2621 hour recordings were analysed. There was a significant correlation between mean ICC and mean ICP wave amplitude and between mean ICC and mean ICP. The mean ICP wave amplitude was significantly higher during the 1 hour periods with mean ICC<0.5 ml/mmHg and significantly lower during 1 hour periods with mean ICC 1.5–3.0 ml/mmHg. Correspondingly, in the 1591 hour recordings with mean ICP wave amplitude≥5.0 mmHg, mean ICC was significantly lower than in the 103 recordings with mean ICP wave amplitude<5.0 mmHg. Mean ICP was normal (i.e. <20 mmHg) in 260 of 262 (99.2%) of the 1 hour recordings; in the 491 hour recordings with mean ICP>15 mmHg, mean ICC was significantly lower than in the 213 recordings with mean ICP<15.0 mmHg.Conclusion: In this cohort of pressure recordings, there was a strong association between ICC and intracranial pulse pressure amplitude. There also was a strong association between ICC and mean ICP, but mean ICP was normal in 260 of 2621 hour recordings (99.2%).

Is Intracranial Pressure Waveform Analysis Useful in the Management of Pediatric Neurosurgical Patients?

Background: We have reported casuistic observations that intracranial pressure (ICP) waveform analysis may be useful in the management of pediatric patients. Method: We here report our whole patient material of 65 children undergoing ICP monitoring with storage of their ICP raw data files during the years 2002–2005. We retrospectively explored the clinical symptoms/findings and radiological cerebral ventricular size before ICP monitoring. Mean ICP was the actively treated ICP parameter. Using an algorithm for identification of cardiac-beat-induced pressure waves we retrospectively determined the mean ICP wave amplitude and latency, in addition to mean ICP. Outcome with regard to change in symptoms/findings during a 1-year period was determined in 55 children. Results: The material includes children with hydrocephalus, craniosynostosis, shunt failure, benign intracranial hypertension and others. The ICP recordings gave wrong diagnostic information due to bad signal quality in 5 of 65 patients (7.7%). The mean ICP wave amplitude was increased in those with papilledema, lethargy and nausea. The main observations were that the mean ICP wave amplitude (not mean ICP) was increased in those that improved from clinical symptoms/findings after treatment and in those that were unchanged/worse after not being treated. Conclusions: Waveform analysis with computation of the mean ICP wave amplitude was more useful by providing information about the quality of the ICP recording, by comparing better with the symptoms/findings at the time of ICP monitoring and by best predicting outcome. Most significantly, 14 of 55 patients (25%) with high amplitudes and left untreated did not recover spontaneously.

Association between intracranial, arterial pulse pressure amplitudes and cerebral autoregulation in head injury patients

Objective: To explore whether intracranial pulse pressure amplitudes relate to arterial pulse pressure amplitudes and whether correlations between time-related changes in intracranial and arterial pulse pressure amplitudes associate with indices of cerebral autoregulation.Methods: A total of 257 continuous and simultaneous intracranial pressure (ICP), arterial blood pressure (ABP) and middle cerebral artery (MCA) blood velocity recordings were obtained 1–14 days after ictus in 76 traumatic head injury patients and analysed retrospectively. Clinical outcome was assessed using the Glasgow outcome scale (GOS). Pulse pressure amplitudes of corresponding single ICP and ABP waves were correlated in consecutive 200 wave pairs. Mean ICP, mean ABP and mean ICP wave amplitudes, and mean and systolic MCA blood flow velocities, were computed in consecutive 6 second time windows. The indices of cerebral autoregulation PRx (moving correlation between mean ICP and mean ABP), and Mx and Sx (moving correlation between mean and systolic MCA blood velocity and cerebral perfusion pressure) were calculated over 4 minute periods and averaged over each recording.Results: Intracranial pulse pressure amplitudes were not related to arterial pulse pressure amplitudes (mean of Pearson's correlations coefficients: 0.04). Outcome was related to mean ICP, PRx and Sx (p ≤ 0.04, multiple regression analysis). Correlations between intracranial and arterial pulse pressure amplitudes were weakly related to PRx (Pearson's correlation coefficient: 0.16; p=0.01), but were not related to the indices of cerebral autoregulation Mx (Pearson's correlation coefficient: 0.07) and Sx (Pearson's correlation coefficient: 0.04).Conclusions: In this cohort of pressure recordings, we found no evidence of a correlation between intracranial and arterial blood pressure amplitudes. The correlation appeared not to be related to the state of cerebral autoregulation, although a weak correlation was found with pressure reactivity index PRx.

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

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