Assessment of intracranial dynamics in hydrocephalus: effects of viscoelasticity on the outcome of infusion tests

Authors: Bottan S, Schmid Daners M, de Zelicourt D, Fellner N, Poulikakos D, Kurtcuoglu V.

Object The treatment of hydrocephalus requires insight into the intracranial dynamics in the patient. Resistance to CSF outflow (R0) is a clinically obtainable parameter of intracranial fluid dynamics that quantifies the apparent resistance to CSF absorption. It is used as a criterion for the selection of shunt candidates and serves as an indicator of shunt performance. The R0 is obtained clinically by performing 1 of 3 infusion tests: constant flow, constant pressure, or bolus infusion. Among these, the bolus infusion method has the shortest examination times and provides the shortest time of exposure of patients to artificially increased intracranial pressure (ICP) levels. However, for unknown reasons, the bolus infusion method systematically underestimates the R0. Here, the authors have tested and verified the hypothesis that this underestimation is due to lack of accounting for viscoelasticity of the craniospinal space in the calculation of the R0. Methods The authors developed a phantom model of the human craniospinal space in order to reproduce in vivo pressure-volume (PV) relationships during infusion testing. The phantom model followed the Marmarou exponential PV equation and also included a viscoelastic response to volume changes. Parameters of intracranial fluid dynamics, such as the R0, could be controlled and set independently. In addition to the phantom model, the authors designed a computational framework for virtual infusion testing in which viscoelasticity can be turned on or off in a controlled manner. Constant flow, constant pressure, and bolus infusion tests were performed on the phantom model, as well as on the virtual computational platform, using standard clinical protocols. Values for the R0 were derived from each infusion test by using both a standard method based on the Marmarou PV equation and a novel method based on a system identification approach that takes into account viscoelastic behavior. Results Experiments with the phantom model confirmed clinical observations that both the constant flow and constant pressure infusion tests, but not the bolus infusion test, yield correct R0 values when they are determined with the standard method according to Marmarou. Equivalent results were obtained using the computational framework. When the novel system identification approach was used to determine the R0, all of the 3 infusion tests yielded correct values for the R0. Conclusions The authors' investigations demonstrate that intracranial dynamics have a substantial viscoelastic component. When this viscoelastic component is taken into account in calculations, the R0, is no longer underestimated in the bolus infusion test.

Research on simulation and experiment of noninvasive intracranial pressure monitoring based on acoustoelasticity effects

Authors: Wu J, He W, Chen WM, Zhu L.

The real-time monitoring of intracranial pressure (ICP) is very important for craniocerebrally critically ill patients, but it is very difficult to realize long-time monitoring for the traditional invasive method, which very easily infects patients. Many noninvasive methods have emerged, but these have not been able to monitor ICP for long periods in real time, and they are not ready for clinical application. In order to realize long-time, online, real-time, noninvasive monitoring for ICP, a new method based on acoustoelasticity of ultrasound is herein proposed. Experimental models were devised to research the new method for experiment and simulation. Polymethyl methacrylate and hydrogel were adopted for the experiment, and their mechanical properties were very close to the real brain. A numerical solution for acoustoelasticity theory was acquired by simulating calculation based on a finite-element method. This was compared to the experimental value. The results showed a consistent match between theoretical solution and experimental value, with maximum error at most 5%. Thus, the effectiveness of the new method was verified. Theoretical and practical foundation is provided for this new method, and it could be used for animal experimentation or clinical testing in further research.

Intracranial atherosclerosis

Authors: Qureshi AI, Caplan LR.

Atherosclerotic disease often involves the intracranial arteries including those encased by cranial bones and dura, and those located in the subarachnoid space. Age, hypertension, and diabetes mellitus are independent risk factors for intracranial atherosclerosis. Intracranial atherosclerosis can result in thromboembolism with or without hypoperfusion leading to transient or permanent cerebral ischaemic events. High rates of recurrent ischaemic stroke and other cardiovascular events mandate early diagnosis and treatment. Present treatment is based on a combination of antiplatelet drugs, optimisation of blood pressure and LDL cholesterol values, and intracranial angioplasty or stent placement, or both, in selected patients.

Study of therapeutic hypothermia (32 to 35°C) for intracranial pressure reduction after traumatic brain injury (the Eurotherm3235Trial): outcome of the pilot phase of the trial

Authors: Andrews PJ, Sinclair LH, Harris B, Baldwin MJ, Battison CG, Rhodes JK, Murray G, De Backer D.

BACKGROUND: Clinical trials in traumatic brain injury (TBI) are challenging. Previous trials of complex interventions were conducted in high-income countries, reported long lead times for site setup and low screened-to-recruitment rates.In this report we evaluate the internal pilot phase of an international, multicentre TBI trial of a complex intervention to assess: design and implementation of an online case report form; feasibility of recruitment (sites and patients); feasibility and effectiveness of delivery of the protocol.
METHODS: All aspects of the pilot phase of the trial were conducted as for the main trial. The pilot phase had oversight by independent Steering and Data Monitoring committees.
RESULTS: Forty sites across 12 countries gained ethical approval. Thirty seven of 40 sites were initiated for recruitment. Of these, 29 had screened patients and 21 randomized at least one patient. Lead times to ethics approval (6.8 weeks), hospital approval (18 weeks), interest to set up (61 weeks), set up to screening (11 weeks), and set up to randomization (31.6 weeks) are comparable with other international trials. Sixteen per cent of screened patients were eligible. We found 88% compliance rate with trial protocol.
CONCLUSION: The pilot data demonstrated good feasibility for this large international multicentre randomized controlled trial of hypothermia to control intracranial pressure. The sample size was reduced to 600 patients because of homogeneity of the patient group and we showed an optimized cooling intervention could be delivered.Trial registration Current Controlled Trials: ISRCTN34555414.

Intracranial hypotension masquerading as nonconvulsive status epilepticus

Authors: Hedna VS, Kumar A, Miller B, Bidari S, Salardini A, Waters MF, Hella M, Valenstein E, Eisenschenk S.

Intracranial hypotension (IH) has been a known entity in neurocritical care since 1938. Even though many cases are spontaneous, the incidence of intracranial hypotension in the neurocritical care setting is increasing by virtue of the increased number of neurosurgical interventions. Whether spontaneous or secondary in etiology, diagnosis of IH usually requires the presence of orthostatic symptoms, including headaches and nausea with low opening CSF pressure. However, typical clinical features in the appropriate clinical context and imaging, even with normal CSF pressure, can indicate IH. In the neurocritical care setting, challenges for accurate semiology include altered sensorium and reduced levels of responsiveness for which many etiologies may exist, including metabolic dysfunction, traumatic brain injury, IH, or nonconvulsive status epilepticus (NCSE). The authors describe 3 patients whose clinical picture and electroencephalography (EEG) findings initially suggested NCSE but who did not respond to treatment with antiepileptic drugs alone. Neuroimaging suggested IH, and subsequent treatment of IH successfully improved the patient's clinical status. To the authors' knowledge this paper is the first in the literature that reports a correlation of IH with electrographic findings similar to NCSE as cause and effect. The authors' hypothesis is that thalamocortical dysfunction causes EEG findings that appear to be similar to those in NCSE but that these conditions do not coexist. The EEG activity is not epileptogenic, and IH results in blocking network pathways producing thalamocortical dysfunction. The authors discuss the hypothesis and pathophysiology of these epileptiform changes in relation to IH.

Effects of Nursing Interventions on Intracranial Pressure

Authors: Olson DM, McNett MM, Lewis LS, Riemen KE, Bautista C.

Background Intracranial pressure is a frequent target for goal-directed therapy to prevent secondary brain injury. In critical care settings, nurses deliver many interventions to patients having intracranial pressure monitored, yet few data documenting the immediate effect of these interventions on intracranial pressure are available. Objective To examine the relationship between intracranial pressure and specific nursing interventions observed during routine care. Methods Secondary analysis of prospectively collected observational data. Results During 3118 minutes of observation, 11 specific nursing interventions were observed for 28 nurse-patient dyads from 16 hospitals. Family members talking in the room, administering sedatives, and repositioning the patient were associated with a significantly lower intracranial pressure. However, intracranial pressure was sometimes higher, lower, or unchanged after each intervention observed. Conclusion Response of intracranial pressure to nursing interventions is inconsistent. Most interventions were associated with inconsistent changes in intracranial pressure at 1 or 5 minutes after the intervention.

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