817 Robotic Semi-Automated Transcranial Doppler Assessment of Cerebrovascular Autoregulation in Post Concussional Syndrome: Methodological Considerations

Introduction

Method

Results

Conclusions

Cortical metabolic changes and clinical outcome in normal pressure hydrocephalus after ventriculoperitoneal shunt: Our preliminary results

INTRODUCTION

Our objective was to evaluate the cortical metabolic changes and clinical outcome in patients affected by idiopathic normal pressure hydrocephalus (iNPH) after a placement of ventriculoperitoneal (VP) shunt.

MATERIALS AND METHODS

10 patients affected by suspected iNPH underwent a CSF hydrodynamics evaluation based on a lumbar infusion test (LIT). The main selection criterion for surgery was based on intracranial elasticity (IE)>0.30. All subjects with an IE>0.30 underwent a PET scan with 18 fluorodeoxiglucose (¹⁸F-FDG) at baseline (PET1) and 1 month after surgery (PET2). Furthermore, the same patients were submitted to clinical evaluation before and 1 month after surgery through neuropsychological tests and gait analysis.

RESULTS

An overall number of 20 18F-FDG PET scans were performed in all the enrolled patients. As compared to PET1, PET2 showed an increase in glucose consumption in the left frontal and left parietal lobe in PET2 as compared to PET1 (P<.001). All the enrolled patients presented a significant increase in neuropsychological scores (i.e Frontal Assessment Battery and Montreal Cognitive Assessment) and have clinically improved at gait analysis. A significant correlation was found between the increase of cortical glucose consumption in the left parietal area and the cognitive improvement as detectable by neuropsychological assessment.

CONCLUSIONS

Improvement in 18F FDG PET glucose metabolism could be considered a useful imaging marker for the assessment of iNPH response to VP shunting.

Effects of pneumoperitoneum and Trendelenburg position on intracranial pressure assessed using different non-invasive methods

BACKGROUND

The laparoscopic approach is becoming increasingly frequent for many different surgical procedures. However, the combination of pneumoperitoneum and Trendelenburg positioning associated with this approach may increase the patient's risk for elevated intracranial pressure (ICP). Given that the gold standard for the measurement of ICP is invasive, little is known about the effect of these common procedures on ICP.

METHODS

We prospectively studied 40 patients without any history of cerebral disease who were undergoing laparoscopic procedures. Three different methods were used for non-invasive estimation of ICP: ultrasonography of the optic nerve sheath diameter (ONSD); transcranial Doppler-based (TCD) pulsatility index (ICP_PI); and a method based on the diastolic component of the TCD cerebral blood flow velocity (ICP_FVd). The ONSD and TCD were measured immediately after induction of general anaesthesia, after pneumoperitoneum insufflation, after Trendelenburg positioning, and again at the end of the procedure.

RESULTS

The ONSD, ICP_FVd, and ICP_PI increased significantly after the combination of pneumoperitoneum insufflation and Trendelenburg positioning. The ICP_FVd showed an area under the curve of 0.80 [95% confidence interval (CI) 0.70-0.90] to distinguish the stage associated with the application of pneumoperitoneum and Trendelenburg position; ONSD and ICP_PI showed an area under the curve of 0.75 (95% CI 0.65-0.86) and 0.70 (95% CI 0.58-0.81), respectively.

CONCLUSIONS

The concomitance of pneumoperitoneum and the Trendelenburg position can increase ICP as estimated with non-invasive methods. In high-risk patients undergoing laparoscopic procedures, non-invasive ICP monitoring through a combination of ONSD ultrasonography and TCD-derived ICP_FVd could be a valid option to assess the risk of increased ICP.

ICP Versus Laser Doppler Cerebrovascular Reactivity Indices to Assess Brain Autoregulatory Capacity

BACKGROUND

To explore the relationship between various autoregulatory indices in order to determine which approximate small vessel/microvascular (MV) autoregulatory capacity most accurately.

METHODS

Utilizing a retrospective cohort of traumatic brain injury patients (N = 41) with: transcranial Doppler (TCD), intracranial pressure (ICP) and cortical laser Doppler flowmetry (LDF), we calculated various continuous indices of autoregulation and cerebrovascular responsiveness: A. ICP derived [pressure reactivity index (PRx)-correlation between ICP and mean arterial pressure (MAP), PAx-correlation between pulse amplitude of ICP (AMP) and MAP, RAC-correlation between AMP and cerebral perfusion pressure (CPP)], B. TCD derived (Mx-correlation between mean flow velocity (FVm) and CPP, Mx_a-correlation between FVm and MAP, Sx-correlation between systolic flow velocity (FVs) and CPP, Sx_a-correlation between FVs and MAP, Dx-correlation between diastolic flow index (FVd) and CPP, Dx_a-correlation between FVd and MAP], and LDF derived (Lx-correlation between LDF cerebral blood flow [CBF] and CPP, Lx_a-correlation between LDF-CBF and MAP). We assessed the relationship between these indices via Pearson correlation, Friedman test, principal component analysis (PCA), agglomerative hierarchal clustering (AHC), and k-means cluster analysis (KMCA).

RESULTS

LDF-based autoregulatory index (Lx) was most associated with TCD-based Mx/Mx_a and Dx/Dx_a across Pearson correlation, PCA, AHC, and KMCA. Lx was only remotely associated with ICP-based indices (PRx, PAx, RAC). TCD-based Sx/Sx_a was more closely associated with ICP-derived PRx, PAx and RAC. This indicates that vascular-derived indices of autoregulatory capacity (i.e., TCD and LDF based) covary, with Sx/Sx_a being the exception, whereas indices of cerebrovascular reactivity derived from pulsatile CBV (i.e., ICP indices) appear to not be closely related to those of vascular origin.

CONCLUSIONS

Transcranial Doppler Mx is the most closely associated with LDF-based Lx/Lx_a. Both Sx/Sx-a and the ICP-derived indices appear to be dissociated with LDF-based cerebrovascular reactivity, leaving Mx/Mx-a as a better surrogate for the assessment of cortical small vessel/MV cerebrovascular reactivity. Sx/Sx_a cocluster/covary with ICP-derived indices, as seen in our previous work.

Occurrence of CPPopt Values in Uncorrelated ICP and ABP Time Series

OBJECTIVES

Optimal cerebral perfusion pressure (CPPopt) is a concept that uses the pressure reactivity (PRx)-CPP relationship over a given period to find a value of CPP at which PRx shows best autoregulation. It has been proposed that this relationship be modelled by a U-shaped curve, where the minimum is interpreted as being the CPP value that corresponds to the strongest autoregulation. Owing to the nature of the calculation and the signals involved in it, the occurrence of CPPopt curves generated by non-physiological variations of intracranial pressure (ICP) and arterial blood pressure (ABP), termed here "false positives", is possible. Such random occurrences would artificially increase the yield of CPPopt values and decrease the reliability of the methodology.In this work, we studied the probability of the random occurrence of false-positives and we compared the effect of the parameters used for CPPopt calculation on this probability.

MATERIALS AND METHODS

To simulate the occurrence of false-positives, uncorrelated ICP and ABP time series were generated by destroying the relationship between the waves in real recordings. The CPPopt algorithm was then applied to these new series and the number of false-positives was counted for different values of the algorithm's parameters.

RESULTS

The percentage of CPPopt curves generated from uncorrelated data was demonstrated to be 11.5%.

CONCLUSION

This value can be minimised by tuning some of the calculation parameters, such as increasing the calculation window and increasing the minimum PRx span accepted on the curve.

"Solid Red Line": An Observational Study on Death from Refractory Intracranial Hypertension

The index of cerebrovascular pressure reactivity (PRx) correlates independently with outcome after traumatic brain injury (TBI). However, as an index plotted in the time domain, PRx is rather noisy. To "organise" PRx and make its interpretation easier, the colour coding of values, with green when PRx <0 and red when PRx> 0.3, has been introduced as a horizontal colour bar on the ICM+ screen. In rare cases of death from refractory intracranial hypertension, an increase in intracranial pressure (ICP) is commonly preceded by values of PRx >0.3, showing a "solid red line".Twenty patients after TBI and one after traumatic subarachnoid haemorrhage (SAH) from six centres in Europe and Australia have been studied. All of them died in a scenario of refractory intracranial hypertension. In the majority of cases the initial ICP was below 20 mmHg and finally increased to values well above 60 mmHg, resulting in cerebral perfusion pressure less than 20 mmHg. In three cases initial ICP was elevated at the start of monitoring. A solid red line was observed in all cases preceding an increase in ICP above 25 mmHg by minutes to hours and in two cases by 2 and 3 days, respectively. If a solid red line is observed over a prolonged period, it should be considered as an indicator of deep cerebrovascular deterioration.

Comparison of ventricular drain location and infusion test in hydrocephalus

OBJECTIVES

Suspected cerebrospinal fluid shunt (CSF) dysfunction in hydrocephalic patients poses a diagnostic uncertainty. The clinical picture can be non-specific and CT imaging alone is not always pathognomonic. Infusion tests are an increasingly used investigation for real-time hydrodynamic assessment of shunt patency. We report the correlation between infusion test results with the quality of ventricular drain placement on CT scans in a large retrospective group of hydrocephalic patients.

MATERIALS & METHODS

Three hundred and six infusion test results performed in 200 patients were correlated with 306 corresponding CT head scans. Nominal logistic regression was used to correlate shunt catheter position on CT imaging to patency of ventricular drain as determined by infusion tests.

RESULTS

Infusion test results of shunt patency are statistically congruent with the analysis of shunt catheter position on CT head scans. Catheter tips completely surrounded by either parenchyma or CSF on CT imaging are strongly associated with evidence of occlusion or patency from infusion tests, respectively (χ² = 51.68, P < 0.0001, n = 306 and χ² = 31.04, P < 0.0001, n = 306).

CONCLUSIONS

The most important anatomical factor for shunt patency is the catheter tip being completely surrounded by CSF. Infusion tests provide functional and reliable assessment of shunt patency in vivo and are strongly correlated with the position of the ventricular catheter on CT imaging.

Non-invasive Monitoring of Intracranial Pressure Using Transcranial Doppler Ultrasonography: Is It Possible?

Although intracranial pressure (ICP) is essential to guide management of patients suffering from acute brain diseases, this signal is often neglected outside the neurocritical care environment. This is mainly attributed to the intrinsic risks of the available invasive techniques, which have prevented ICP monitoring in many conditions affecting the intracranial homeostasis, from mild traumatic brain injury to liver encephalopathy. In such scenario, methods for non-invasive monitoring of ICP (nICP) could improve clinical management of these conditions. A review of the literature was performed on PUBMED using the search keywords 'Transcranial Doppler non-invasive intracranial pressure.' Transcranial Doppler (TCD) is a technique primarily aimed at assessing the cerebrovascular dynamics through the cerebral blood flow velocity (FV). Its applicability for nICP assessment emerged from observation that some TCD-derived parameters change during increase of ICP, such as the shape of FV pulse waveform or pulsatility index. Methods were grouped as: based on TCD pulsatility index; aimed at non-invasive estimation of cerebral perfusion pressure and model-based methods. Published studies present with different accuracies, with prediction abilities (AUCs) for detection of ICP ≥20 mmHg ranging from 0.62 to 0.92. This discrepancy could result from inconsistent assessment measures and application in different conditions, from traumatic brain injury to hydrocephalus and stroke. Most of the reports stress a potential advantage of TCD as it provides the possibility to monitor changes of ICP in time. Overall accuracy for TCD-based methods ranges around ±12 mmHg, with a great potential of tracing dynamical changes of ICP in time, particularly those of vasogenic nature.

Intracranial pressure, its components and cerebrospinal fluid pressure-volume compensation

Clinical measurement of intracranial pressure (ICP) is often performed to aid diagnosis of hydrocephalus. This review discusses analysis of ICP and its components' for the investigation of cerebrospinal fluid (CSF) dynamics. The role of pulse, slow and respiratory waveforms of ICP in diagnosis, prognostication and management of hydrocephalus is presented. Two methods related to ICP measurement are listed: an overnight monitoring of ICP and a constant-rate infusion study. Due to the dynamic nature of ICP, a 'snapshot' manometric measurement of ICP is of limited use as it might lead to unreliable results. Therefore, monitoring of ICP over longer time combined with analysis of its waveforms provides more detailed information on the state of pressure-volume compensation. The infusion study implements ICP signal processing and CSF circulation model analysis in order to assess the cerebrospinal dynamics variables, such as CSF outflow resistance, compliance of CSF space, pressure amplitude, reference pressure, and CSF formation. These parameters act as an aid tool in diagnosis and prognostication of hydrocephalus and can be helpful in the assessment of a shunt malfunction.

Non-invasive assessment of intracranial pressure

Monitoring of intracranial pressure (ICP) is invaluable in the management of neurosurgical and neurological critically ill patients. Invasive measurement of ventricular or parenchymal pressure is considered the gold standard for accurate measurement of ICP but is not always possible due to certain risks. Therefore, the availability of accurate methods to non-invasively estimate ICP has the potential to improve the management of these vulnerable patients. This review provides a comparative description of different methods for non-invasive ICP measurement. Current methods are based on changes associated with increased ICP, both morphological (assessed with magnetic resonance, computed tomography, ultrasound, and fundoscopy) and physiological (assessed with transcranial and ophthalmic Doppler, tympanometry, near-infrared spectroscopy, electroencephalography, visual-evoked potentials, and otoacoustic emissions assessment). At present, none of the non-invasive techniques alone seem suitable as a substitute for invasive monitoring. However, following the present analysis and considerations upon each technique, we propose a possible flowchart based on the combination of non-invasive techniques including those characterizing morphologic changes (e.g., repetitive US measurements of ONSD) and those characterizing physiological changes (e.g., continuous TCD). Such an integrated approach, which still needs to be validated in clinical practice, could aid in deciding whether to place an invasive monitor, or how to titrate therapy when invasive ICP measurement is contraindicated or unavailable.

Intraoperative non invasive intracranial pressure monitoring during pneumoperitoneum: a case report and a review of the published cases and case report series

Non-invasive measurement of ICP (nICP) can be warranted in patients at risk for developing increased ICP during pneumoperitoneum (PP). Our aim was to assess available data on the application of nICP monitoring during these procedures and to present a patient assessed with an innovative combination of noninvasive tools. Literature review of nICP assessment during PP did not find any studies comparing different methods intraprocedurally and only few studies of any nICP monitoring were available: transcranial Doppler (TCD) studies used the pulsatility index (PI) as an estimator of ICP and failed to detect a significant ICP increase during PP, whereas two out of three optic nerve sheath diameter (ONSD) studies detected a statistically significant ICP increase. In the case study, we describe a 52 year old man with a high grade thalamic glioma who underwent urgent laparoscopic cholecystectomy. Considering the high intraoperative risk of developing intracranial hypertension, he was monitored through parallel ONSD ultrasound measurement and TCD derived formulae (flow velocity diastolic formula, FVdnICP, and PI). ONSD and FVdnICP methods indicated a significant ICP increase during PP, whereas PI was not significantly increased. Our experience, combined with the literature review, seems to suggest that PI might not detect ICP changes in this context, however we indicate a possible interest of nICP monitoring during PP by means of ONSD and of TCD derived FVdNICP, especially for patients at risk for increased ICP.

Heart rate passivity of cerebral tissue oxygenation is associated with predictors of poor outcome in preterm infants

AIM

Near-infrared spectroscopy (NIRS) and transcranial Doppler (TCD) allow non-invasive assessment of cerebral haemodynamics. We assessed cerebrovascular reactivity in preterm infants by investigating the relationship between NIRS- and TCD-derived indices and correlating them with severity of clinical illness.

METHODS

We recorded the NIRS-derived cerebral tissue oxygenation index (TOI) and TCD-derived flow velocity (Fv), along with other physiological variables. Moving correlation coefficients between measurements of cerebral perfusion (TOI, Fv) and heart rate were calculated. We presumed that positivity of these correlation coefficients - tissue oxygenation heart rate reactivity index (TOHRx) and flow velocity heart rate reactivity index (FvHRx) - would indicate a direct relationship between cerebral perfusion and cardiac output representing impaired cerebrovascular autoregulation.

RESULTS

We studied 31 preterm infants at a median age of 2 days, born at a median gestational age of 26 + 1 weeks. TOHRx was significantly correlated with gestational age (R = -0.57, p = 0.007), birth weight (R = -0.58, p = 0.006) and the Clinical Risk Index for Babies II (R = 0.55, p = 0.0014). TOHRx and FvHRx were significantly correlated (R = 0.39, p = 0.028).

CONCLUSION

Heart rate has a key influence on cerebral haemodynamics in preterm infants, and TOHRx may be of diagnostic value in identifying impaired cerebrovascular reactivity leading to adverse clinical outcome.

Repeatability of cerebrospinal fluid constant rate infusion study

OBJECTIVE

Infusion tests are important tools to assess cerebrospinal fluid (CSF)dynamics used in the preoperative selection of patients for shunt surgery, or to predict the scope of improvement from shunt revision. The aim of this study was to assess the repeatability of the key quantitative parameters describing CSF dynamics that are determined with infusion testing.

MATERIALS AND METHODS

Eighteen patients in whom a constant infusion test was repeated within 102 days, without any intermediate surgical intervention, were studied. From each test baseline ICP, baseline pulse amplitude, outflow resistance, elastance coefficient and slope of the amplitude-pressure line were calculated and investigated with a regression and Bland-Altman analysis.

RESULTS

Significant correlations (P < 0.01) were found for the outflow resistance (R = 0.96), the elastance coefficient (R = 0.778) and the slope of the amplitude-pressure line (R = 0.876). The estimated 95% confidence level for outflow resistance was 3 mmHg/ml min. Likewise, the elastance coefficient lay within a range of 0.16/ml and the slope of the amplitude-pressure line within 0.25. The most inconsistent parameter found were baseline ICP (R = 0.272) and baseline pulse amplitude (R = 0.171).

CONCLUSION

The results of this study imply that the parameters resulting from an infusion study have to be considered within a range rather than as an absolute value.

Pulsatile intracranial pressure and cerebral autoregulation after traumatic brain injury

BACKGROUND

Strong correlation between mean intracranial pressure (ICP) and its pulse wave amplitude (AMP) has been demonstrated in different clinical scenarios. We investigated the relationship between invasive mean arterial blood pressure (ABP) and AMP to explore its potential role as a descriptor of cerebrovascular pressure reactivity after traumatic brain injury (TBI).

METHODS

We retrospectively analyzed data of patients suffering from TBI with brain monitoring. Transcranial Doppler blood flow velocity, ABP, ICP were recorded digitally. Cerebral perfusion pressure (CPP) and AMP were derived. A new index-pressure-amplitude index (PAx)-was calculated as the Pearson correlation between (averaged over 10 s intervals) ABP and AMP with a 5 min long moving average window. The previously introduced transcranial Doppler-based autoregulation index Mx was evaluated in a similar way, as the moving correlation between blood flow velocity and CPP. The clinical outcome was assessed after 6 months using the Glasgow outcome score.

RESULTS

293 patients were studied. The mean PAx was -0.09 (standard deviation 0.21). This negative value indicates that, on average, an increase in ABP causes a decrease in AMP and vice versa. PAx correlated strong with Mx (R (2) = 0.46, P < 0.0002). PAx also correlated with age (R (2) = 0.18, P < 0.05). PAx was found to have as good predictive outcome value (area under curve 0.71, P < 0.001) as Mx (area under curve 0.69, P < 0.001).

CONCLUSIONS

We demonstrated significant correlation between the known cerebral autoregulation index Mx and PAx. This new index of cerebrovascular pressure reactivity using ICP pulse wave information showed to have a strong association with outcome in TBI patients.

Dynamic cerebral autoregulation associates with infarct size and outcome after ischemic stroke

OBJECTIVES

Cerebral autoregulation is particularly challenged in acute ischemic stroke. We investigated (1) clinical and radiological factors related to dynamic cerebral autoregulation (DCA) in acute stroke and (2) the relationship between DCA and clinical outcome of stroke.

METHODS

A total of 45 patients with middle cerebral artery (MCA) stroke were analyzed pooling two previous studies. DCA was measured by transcranial Doppler in both MCAs early (within 48 h from onset) and late (day 5-7) using low-frequency phase and correlation analysis (index Mx). Outcome was assessed by modified Rankin scale after a mean period of 4 months.

RESULTS

Mx increased (i.e. autoregulation worsened) between the early and late measurement, more so on affected (P = 0.005) than on unaffected sides (P = 0.014). Poorer autoregulation as indicated by lower ipsilateral phase (early and late) and higher Mx (late measurement) were significantly related to larger infarction. More severe stroke was significantly related to poorer ipsilateral Mx and phase. Ipsilateral phase in the early (P = 0.019) and Mx in the late measurement (P =0..016) were related to poor clinical outcome according to univariate analysis.

CONCLUSIONS

Impairment of DCA ipsilateral to acute ischemic stroke is associated with larger infarction. Dysautoregulation tends to worsen and spread to the contralateral side over the first days post-stroke and is associated with poor clinical outcome.

What comes first? The dynamics of cerebral oxygenation and blood flow in response to changes in arterial pressure and intracranial pressure after head injury

BACKGROUND

Brain tissue partial oxygen pressure (Pbt(O(2))) and near-infrared spectroscopy (NIRS) are novel methods to evaluate cerebral oxygenation. We studied the response patterns of Pbt(O(2)), NIRS, and cerebral blood flow velocity (CBFV) to changes in arterial pressure (AP) and intracranial pressure (ICP).

METHODS

Digital recordings of multimodal brain monitoring from 42 head-injured patients were retrospectively analysed. Response latencies and patterns of Pbt(O(2)), NIRS-derived parameters [tissue oxygenation index (TOI) and total haemoglobin index (THI)], and CBFV reactions to fluctuations of AP and ICP were studied.

RESULTS

One hundred and twenty-one events were identified. In reaction to alterations of AP, ICP reacted first [4.3 s; inter-quartile range (IQR) -4.9 to 22.0 s, followed by NIRS-derived parameters and CBFV (10.9 s; IQR: -5.9 to 39.6 s, 12.1 s; IQR: -3.0 to 49.1 s, 14.7 s; IQR: -8.8 to 52.3 s for THI, CBFV, and TOI, respectively), with Pbt(O(2)) reacting last (39.6 s; IQR: 16.4 to 66.0 s). The differences in reaction time between NIRS parameters and Pbt(O(2)) were significant (P<0.001). Similarly when reactions to ICP changes were analysed, NIRS parameters preceded Pbt(O(2)) (7.1 s; IQR: -8.8 to 195.0 s, 18.1 s; IQR: -20.6 to 80.7 s, 22.9 s; IQR: 11.0 to 53.0 s for THI, TOI, and Pbt(O(2)), respectively). Two main patterns of responses to AP changes were identified. With preserved cerebrovascular reactivity, TOI and Pbt(O(2)) followed the direction of AP. With impaired cerebrovascular reactivity, TOI and Pbt(O(2)) decreased while AP and ICP increased. In 77% of events, the direction of TOI changes was concordant with Pbt(O(2)).

CONCLUSIONS

NIRS and transcranial Doppler signals reacted first to AP and ICP changes. The reaction of Pbt(O(2)) is delayed. The results imply that the analysed modalities monitor different stages of cerebral oxygenation.

Effect of age on intraoperative cerebrovascular autoregulation and near-infrared spectroscopy-derived cerebral oxygenation

BACKGROUND

Age is an important risk factor for perioperative cerebral complications such as stroke, postoperative cognitive dysfunction, and delirium. We explored the hypothesis that intraoperative cerebrovascular autoregulation is less efficient and brain tissue oxygenation lower in elderly patients, thus, increasing the vulnerability of elderly brains to systemic insults such as hypotension.

METHODS

We monitored intraoperative cerebral perfusion in 50 patients aged 18-40 and 77 patients >65 yr at two Swiss university hospitals. Mean arterial pressure (MAP) was measured continuously using a plethysmographic method. An index of cerebrovascular autoregulation (Mx) was calculated based on changes in transcranial Doppler flow velocity due to changes in MAP. Cerebral oxygenation was assessed by the tissue oxygenation index (TOI) using near-infrared spectroscopy. End-tidal CO₂, O₂, and sevoflurane concentrations and peripheral oxygen saturation were recorded continuously. Standardized anaesthesia was administered in all patients (thiopental, sevoflurane, fentanyl, atracurium).

RESULTS

Autoregulation was less efficient in patients aged >65 yr [by 0.10 (se 0.04; P=0.020)] in a multivariable linear regression analysis. This difference was not attributable to differences in MAP, end-tidal CO₂, or higher doses of sevoflurane. TOI was not significantly associated with age, sevoflurane dose, or Mx but increased with increasing flow velocity [by 0.09 (se 0.04; P=0.028)] and increasing MAP [by 0.11 (se 0.05; P=0.043)].

CONCLUSIONS

Our results do not support the hypothesis that older patients' brains are more vulnerable to systemic insults. The difference of autoregulation between the two groups was small and most likely clinically insignificant.

Clinical assessment of cerebrospinal fluid dynamics in hydrocephalus. Guide to interpretation based on observational study

OBJECTIVES

The term hydrocephalus encompasses a range of disorders characterised by clinical symptoms, abnormal brain imaging and derangement of cerebrospinal fluid (CSF) dynamics. The ability to elucidate which patients would benefit from CSF diversion (a shunt or third ventriculostomy) is often unclear. Similar difficulties are often encountered in shunted patients to predict the scope for improvement by shunt re-adjustment or revision. In this study we aimed to update our knowledge of how key quantitative parameters describing CSF dynamics may be used in diagnosis of shunt-responsive hydrocephalus and in the assessment of shunt function.

METHODS

A number of quantitative parameters [including resistance to CSF outflow (Rcsf), pulse amplitude of intracranial pressure waveform (AMP), RAP index and slow vasogenic waves] were studies in 1423 patients with 2665 CSF infusion tests and 305 overnight intracranial pressure (ICP)-monitoring sessions over a 17 year period.

OBSERVATIONS

We demonstrate our observations for typical values of Pb, Rcsf, AMP, slow vasogenic waves derived from infusion studies or overnight ICP monitoring in differentiating atrophy from shunt-responsive normal pressure hydrocephalus or acute hydrocephalus. From the same variables tested on shunted patients we demonstrate a standardised approach to help differentiate a properly-functioning shunt from underdrainage or overdrainage.

CONCLUSIONS

Quantitative variables derived from CSF dynamics allow differentiation between clinically overlapping entities such as shunt-responsive normal pressure hydrocephalus and brain atrophy (not shunt responsive) as well as allowing the detection of shunt malfunction (partial or complete blockage) or overdrainage. This observational study is intended to serve as an update for our understanding of quantitative testing of CSF dynamics.

A study of perioperative lumbar cerebrospinal fluid pressure in patients undergoing acoustic neuroma surgery

The objective of this study was to measure changes in cerebrospinal fluid (CSF) pressure and cerebrovascular hemodynamics following acoustic neuroma surgery. The subjects were 32 patients undergoing translabyrinthine or retrosigmoid excision of acoustic neuroma. CSF pressure and the amplitude of the CSF pressure pulse wave were measured using lumbar catheters, and all variables were recorded minute by minute on a microcomputer. Transcranial doppler (TCD) was used to measure flow velocity in the middle cerebral artery in 10 patients to monitor changes in cerebral hemodynamics. In the 24 hours after surgery, all patients showed a statistically significant rise in CSF pressure from 11.4 mm Hg (standard deviation [SD] 6.1) to 19.6 mm Hg (SD 5.2) and a corresponding fall in the compliance of the CSF compartment. These changes were reversed within 48 hours, and the CSF pressure fell below the preoperative level over the next 4 days without any drainage of CSF. The results of this study demonstrate a transient increase in CSF pressure and decrease in craniospinal compliance that is provoked by surgery. The most plausible explanation for this disturbance is impaired CSF absorption, which resolves rapidly in most patients without therapeutic CSF drainage.

Impact of duration of symptoms on CSF dynamics in idiopathic normal pressure hydrocephalus

OBJECTIVE

Cerebrospinal fluid (CSF) pressure-volume compensation may change over time as part of normal ageing, where the resistance to CSF outflow increases and the formation of CSF decreases with age. Is CSF compensation dependent on duration of symptoms in idiopathic normal pressure hydrocephalus (iNPH)?

METHODS

We investigated 92 patients presenting with iNPH. Mean age was 73 (range 47-86). There were 60 men and 32 women. They all presented with gait disturbance and ventricular dilatation. Memory deficit occurred in 72% and urinary incontinence in 52% of patients. All patients underwent computerized CSF infusion tests. Sixty-four shunted patients were available for follow-up, and their improvement was expressed using the NPH score.

RESULTS

Mean intracranial pressure (ICP) was 10.1±5.1 mmHg, and mean resistance to CSF outflow was 17.3±5.2 mmHg/(ml/min). Mean duration of symptoms was 24±19 months (range from 2 weeks to 86 months). Baseline ICP, magnitude of ICP pulse waveform, brain compliance and improvement after shunting (72% of patients improved) did not exhibit any dependency on the duration of symptoms. The resistance to CSF outflow showed a strong tendency to decrease in time with the duration of symptoms beyond 2 years (R= -0.702; P<0.005).

CONCLUSION

This is a preliminary observation, and it suggests that for patients with duration of symptoms longer than 2-3 years, the threshold for normal resistance to CSF outflow should be duration-adjusted.

Autonomic neuropathy is associated with impairment of dynamic cerebral autoregulation in type 1 diabetes

HYPOTHESIS

The mechanisms underlying impairment of dynamic cerebral autoregulation in diabetes are not well known. Cardiovascular autonomic neuropathy (CAN) could contribute to dynamic cerebral autoregulation impairment. In this study, we assessed the association between CAN and impairment of dynamic cerebral autoregulation in patients with type 1 diabetes.

METHODS

We evaluated dynamic cerebral autoregulation (DCA) in patients with type 1 diabetes and no history of cerebrovascular disease. DCA was assessed with transcranial Doppler using the correlation coefficient index Mx method. Mx was calculated from slow changes in mean cerebral blood flow velocity and mean arterial blood pressure. Increase in Mx indicates weaker DCA, with a threshold for impaired DCA above 0.3. Moderate CAN was defined as reduced heart rate variability (HRV) on the following tests: deep controlled breathing, Valsalva maneuver or initiation of active standing. Severe CAN was defined as reduced HRV associated with orthostatic hypotension.

RESULTS

60 patients were included (M/F: 33/27; mean age ± SD: 46 years ± 11.5). 23 patients had moderate CAN and 15 patients severe CAN. DCA was impaired in 37 patients. CAN was associated with impaired DCA (p = 0.005). Impairment of DCA was more pronounced in patients with severe CAN (p = 0.019). Glycosylated haemoglobin (HbA1c) was associated with impaired DCA in univariate analysis (p = 0.05). In multivariate analysis, only CAN was associated with impaired DCA (p = 0.007) whereas HbA1c was not (p = 0.161).

CONCLUSIONS

CAN was associated with impaired DCA in type 1 diabetes. The magnitude of DCA impairment increased with the severity of CAN.

Evaluation of the cerebrovascular pressure reactivity index using non-invasive finapres arterial blood pressure

A pressure reactivity index (PRx) can be assessed in patients with continuous monitoring of arterial blood pressure (ABP) and intracranial pressure (ICP) as a moving correlation coefficient between slow fluctuations of these two signals within a low frequency bandwidth. The study aimed to investigate whether the invasive ABP monitoring can be replaced with non-invasive measurement of ABP using a Finapres plethysmograph (fABP) to calculate the fPRx. There is a well-defined group of patients, suffering from hydrocephalus and undergoing CSF pressure monitoring, which may benefit from such a measurement. 41 simultaneous day-by-day monitoring of ICP, ABP and fABP were performed for about 30 min in 10 head injury patients. A Bland-Altman assessment for agreement was used to compare PRx and fPRx calculations. Performance metrics and the McNemary test were used to determine whether fPRx is sensitive enough to distinguish between functioning and disturbed cerebrovascular pressure reactivity. The fPRx correlated with PRx (R(Spearman) = 0.92, p < 0.001; bias = -0.04; lower and upper limits of agreement: -0.26 and 0.17, respectively). The fPRx distinguished between active and passive reactivity in more than 89% cases. The fPRx can be used with care for assessment of cerebrovascular reactivity in patients for whom invasive ABP measurement is not feasible. The fPRx is sensitive enough to distinguish between functional and deranged reactivity.

In vivo assessment of hydrocephalus shunt

OBJECTIVES

Over a 3-year period, we have performed 312 tests in 197 shunted patients. The data have been analyzed retrospectively to: (1) investigate the parameters describing CSF dynamics that correlate with shunt under-drainage and (2) estimate accuracy of this method.

METHODS

Constant rate infusion tests into shunt prechamber were performed.

RESULTS

In 161 of the 312 infusion tests, results indicated under-draining shunts. Patients in the under-draining group had higher baseline and plateau CSF pressures, higher resistance to CSF outflow and higher levels of baseline pulse amplitude waveform. During the test, a significantly greater vasogenic waves and lower compensatory reserve was noticed in patients with blocked shunts. In 21 patients with suggestion of shunt blockage and who subsequently underwent operative revision of the shunt, reports of intraoperative shunt patency were available. Shunt blockage was confirmed intra-operatively during surgery in 19 cases.

CONCLUSIONS

In vivo shunt testing is easy, safe and clinically useful, aiding decision in difficult clinical situations, where shunt malfunction is suspected but not certain. It also has satisfactory positive predictive power.

Link between vasogenic waves of intracranial pressure and cerebrospinal fluid outflow resistance in normal pressure hydrocephalus

Recent studies on normal pressure hydrocephalus (NPH) have pointed to a possible link between the disturbance in CSF circulation and cerebrovascular factors. We investigated the quantitative relationship between the resistance to CSF outflow (Rcsf) and vasogenic waves of ICP in patients with normal pressure hydrocephalus. Forty-five patients with NPH were investigated by an infusion study. The magnitudes of vasogenic ICP components: pulse, respiratory and slow vasogenic waves were assessed, and compared with Rcsf. Both baseline respiratory and slow waves of ICP were positively correlated with Rcsf. The respiratory wave at baseline was a single independent predictor of Rcsf (r = 0.66, p < 0.0002). All vasogenic components increased significantly during the infusion test. The magnitude of the increase was positively correlated with Rcsf. The vasogenic ICP waves, notably the respiratory wave of ICP, correlate with the resistance to CSF outflow.

How does CSF dynamics change after shunting?

OBJECTIVE

Hydrocephalus is much more complex than a simple disorder of cerebrospinal fluid (CSF) circulation. Shunting primarily corrects disturbed fluid flow which may have an impact on cerebral blood flow and metabolism. We studied hydrocephalic patients before and after shunting to characterize changes in their CSF compensatory parameters.

MATERIAL AND METHODS

We selected 25 patients and studied them retrospectively. All patients had ventriculomegaly and clinical symptoms of normal pressure hydrocephalus. After shunting, they were still presenting with some adverse symptoms, mainly headaches, slow improvement or no improvement of ventriculomegaly. Therefore, they underwent further infusion studies to assess shunt function. In all cases, the shunts were confirmed to be draining CSF adequately. Parameters of CSF dynamics: baseline intracranial pressure (ICP), resistance to CSF outflow, cerebrospinal elasticity, content of vasogenic pressure waves (pulse, respiratory and B waves) and compensatory reserve assessed as moving correlation coefficient between mean CSF pressure and pulse amplitude (RAP), were compared before and after shunting.

RESULTS

Mean ICP and resistance to CSF outflow decreased (P < 0.003) after shunting. All vasogenic pressure waves decreased (P < 0.005). Compensatory reserve (RAP) significantly improved (P < 0.005).

CONCLUSION

A functioning shunt has an important impact on CSF circulation and pressure-volume compensation. Infusion studies can demonstrate the return of disturbed CSF dynamics to normal values even if clinical or radiological changes are not dramatic.

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.

Accuracy of non-invasive ICP assessment can be increased by an initial individual calibration

OBJECTIVE

In a formerly introduced mathematical model, intracranial pressure (ICP) could be non-invasively assessed using cerebral blood flow velocity (FV) and arterial blood pressure (ABP). The current study attempts to check whether the accuracy of the non-invasive ICP assessment (nICP) improves after an initial individual calibration by implanted ICP probes.

METHODS

Thirteen patients with brain lesions (35-77 years, mean: 58 +/- 13 years) were studied. FV, ABP and ICP signals were recorded at days 1, 2, 4 and 7. nICP was calculated and compared to ICP. In the first recording of each patient the (invasively assessed) ICP signal was used to calibrate the nICP calculation procedure, while the follow-up recordings were used for its validation.

FINDINGS

In 11 patients 22 follow-up recordings were performed. The mean deviation between ICP and the original nICP (+/- SD) was 8.3 +/- 7.9 mmHg. Using the calibrated method this deviation was reduced to 6.7 +/- 6.7 mmHg (P < 0.005).

CONCLUSIONS

Initial individual calibration of nICP assessment method significantly improves the accuracy of nICP estimation on subsequent days. This hybrid method of ICP assessment may be used in intensive care units in patients with initially implanted ICP probes. After removal of the probes, ICP monitoring can be continued using the calibrated nICP assessment procedure.

Ventriculostomy for control of raised ICP in acute traumatic brain injury

The aim of this study was to evaluate the effect of ventriculostomy on intracranial pressure (ICP), and related parameters, including cerebrospinal compensation, cerebral oxygenation (PbtO2) and metabolism (microdialysis) in patients with traumatic brain injury (TBI).

MATERIALS AND METHODS

Twenty-four patients with parenchymal ICP sensors were prospectively included in the study. Ventriculostomy was performed after failure to control ICP with initial measures. Monitoring parameters were digitally recorded before and after ventriculostomy and compared using appropriate tests.

RESULTS

In all patients ventriculostomy led to rapid reduction in ICP. Pooled mean daily values of ICP remained < 20mmHg for 72h after ventriculostomy and were lower than before (p < 0.001). In 11 out of 24 patients during the initial 24-h period following ventriculostomy an increase in ICP to values exceeding 20mmHg was observed. In the remaining 13 patients ICP remained stable, allowing reduction in the intensity of treatment. In this group ventriculostomy led to significant improvement in craniospinal compensation (RAP index), cerebral perfusion pressure and PbtO2. Improvement in lactate/pyruvate ratio, a marker of energy metabolism, was correlated with the increase in PbtO2.

CONCLUSION

Ventriculostomy is a useful ICP-lowering manoeuvre, with sustained ICP reduction and related physiological improvements achieved in > 50% of patients.

Pulse amplitude of intracranial pressure waveform in hydrocephalus

BACKGROUND

There is increasing interest in evaluation of the pulse amplitude of intracranial pressure (AMP) in explaining dynamic aspects of hydrocephalus. We reviewed a large number of ICP recordings in a group of hydrocephalic patients to assess utility of AMP.

MATERIALS AND METHODS

From a database including approximately 2,100 cases of infusion studies (either lumbar or intraventricular) and overnight ICP monitoring in patients suffering from hydrocephalus of various types (both communicating and non-communicating), etiology and stage of management (non-shunted or shunted) pressure recordings were evaluated. For subgroup analysis we selected 60 patients with idiopathic NPH with full follow-up after shunting. In 29 patients we compared pulse amplitude during an infusion study performed before and after shunting with a properly functioning shunt. Amplitude was calculated from ICP waveforms using spectral analysis methodology.

FINDINGS

A large amplitude was associated with good outcome after shunting (positive predictive value of clinical improvement for AMP above 2.5 mmHg was 95%). However, low amplitude did not predict poor outcome (for AMP below 2.5 mmHg 52% of patients improved). Correlations of AMP with ICP and Rcsf were positive and statistically significant (N = 131 with idiopathic NPH; R = 0.21 for correlation with mean ICP and 0.22 with Rcsf; p< 0.01). Correlation with the brain elastance coefficient (or PVI) was not significant. There was also no significant correlation between pulse amplitude and width of the ventricles. The pulse amplitude decreased (p < 0.005) after shunting.

CONCLUSIONS

Interpretation of the ICP pulse waveform may be clinically useful in patients suffering from hydrocephalus. Elevated amplitude seems to be a positive predictor for clinical improvement after shunting. A properly functioning shunt reduces the pulse amplitude.

ICM+, a flexible platform for investigations of cerebrospinal dynamics in clinical practice

BACKGROUND

ICM+ software encapsulates 20 years of our experience in brain monitoring gained in multiple neurosurgical and intensive care centres. It collects data from a variety of bedside monitors and produces on-line time trends of parameters defined using configurable signal processing formulas. The resulting data can be displayed in a variety of ways including time trends, histograms, cross histograms, correlations, etc. For technically minded researchers there is a plug-in mechanism facilitating registration of third party libraries of functions and analysis tools.

METHODS

The latest version of the ICM+ software has been used in 162 severely head injured patients in the Neurosciences Critical Care Unit of the Addenbrooke's Cambridge University Hospital. Intracranial pressure (ICP) and invasive arterial blood pressure (ABP) were monitored routinely. Mean values of ICP, ABP, cerebral perfusion pressure (CPP) and various indices describing pressure reactivity (PRx), pressure-volume compensation (RAP) and vascular waveforms of ICP were calculated. Error-bar chart showing reactivity index PRx versus CPP ('Optimal CPP' chart) was calculated continuously.

FINDINGS

PRx showed a significant relationship with CPP (ANOVA: p < 0.021) indicating loss of cerebral pressure-reactivity for low CPP (CPP < 55 mmHg) and for high CPPs (CPP > 95 mmHg). Examining PRx-CPP curves in individual patients revealed that CPP(OPT) not only varied between subjects but tended to fluctuate as the patient's state changed during the stay in the ICU. Calculation window of 6-8 h provided enough data to capture the CPP(OPT) curve.

CONCLUSIONS

ICM+ software proved to be useful both academically and clinically. The complexity of data analysis is hidden inside loadable profiles thus allowing clinically minded investigators to take full advantage of signal processing engine in their research into cerebral blood and fluid dynamics.