Effect of sevoflurane on cerebral perfusion pressure in patients with internal hydrocephalus

Authors: Karwacki Z, Witkowska M, Niewiadomski S, Wiatr A, Dzierżanowski J, Słoniewski P.

BACKGROUND: Due to its confirmed neuroprotective properties, sevoflurane is one of a few anaesthetics used for neuroanaesthesia. Its effects on the cerebral and systemic circulations may be of particular importance in patientswith intracranial pathology. This study aimed to evaluate the effect of sevoflurane at concentrations lower than 1 MAC on cerebral perfusion pressure (CPP) in patients with internal hydrocephalus.
METHODS: The study was conducted on14 patients with internal hydrocephalus, who underwent ventriculo-peritoneal shunt implantation. After inserting the catheter into the lateral cerebral ventricle, sevoflurane, at 1.1 and 2.2 vol%, was initiated at two successive 15-minute intervals. The intracranial pressure (ICP) was continuously measured; special attention was focused on the values prior to and at the end of each observation period. The following parameters were monitored: mean arterial pressure (MAP), CPP, heart rate, end-tidal CO₂ concentration, core body temperature, and the inspiratory and end-expiratory concentrations of sevoflurane.
RESULTS: The HR and MAP decreased during successive observation intervals compared to baseline values. Likewise, the CPP decreased from 75.6 ± 2.8 mm Hg to 72.2 ± 2.6 mm Hg to 70.2 ± 0.8 mm Hg. The baseline value for ICP was 16.3 ± 0.6 mm Hg and increased to 17.7 ± 0.8 and 18.9 ± 0.5 mm Hg during the next observation periods.
CONCLUSIONS: Sevoflurane administered ata concentration below 1MAC to patients with internal hydrocephalus increases the ICP and decreases the MAP, which leads to adecrease in CPP. The CPP decrease is more dependent on depressing the systemic circulatory system than an increased ICP.

CSF dynamic analysis of a predictive pulsatility-based infusion test for normal pressure hydrocephalus

Authors: Qvarlander S, Malm J, Eklund A.

Disturbed cerebrospinal fluid (CSF) dynamics are part of the pathophysiology of normal pressure hydrocephalus (NPH) and can be modified and treated with shunt surgery. This study investigated the contribution of established CSF dynamic parameters to AMPmean, a prognostic variable defined as mean amplitude of cardiac-related intracranial pressure pulsations during 10 min of lumbar constant infusion, with the aim of clarifying the physiological interpretation of the variable. AMPmean and CSF dynamic parameters were determined from infusion tests performed on 18 patients with suspected NPH. Using a mathematical model of CSF dynamics, an expression for AMPmean was derived and the influence of the different parameters was assessed. There was high correlation between modelled and measured AMPmean (r = 0.98, p < 0.01). Outflow resistance and three parameters relating to compliance were identified from the model. Correlation analysis of patient data confirmed the effect of the parameters on AMPmean (Spearman's ρ = 0.58-0.88, p < 0.05). Simulated variations of ±1 standard deviation (SD) of the parameters resulted in AMPmean changes of 0.6-2.9 SD, with the elastance coefficient showing the strongest influence. Parameters relating to compliance showed the largest contribution to AMPmean, which supports the importance of the compliance aspect of CSF dynamics for the understanding of the pathophysiology of NPH.

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.

Low-pressure hydrocephalus: indication for custom-made catheters? Technical report

Authors: Galbarriatu L, Rivero-Garvía M, Olivares M, Miranda D, Pomposo I, Márquez-Rivas J.

BACKGROUND: Low-pressure hydrocephalus (LPH) is characterized by ventriculomegaly with persistent low intracranial pressure (ICP). Sub-zero drainage is needed for its management and multiple solutions have been described. Our aim is to report our experience with custom-made peritoneal catheters with larger inner diameter as an alternative treatment option.
METHODS: We made a retrospective review of all patients diagnosed with LPH and treated with custom-made peritoneal catheters at the Virgen del Rocío Pediatric Neurosurgical Unit. Catheters were coated with antibiotic or silver. The inner diameter of ventricular catheters was 1.4 mm; peritoneal catheters were larger than usual (1.9 mm inner diameter).
RESULTS: We identified four patients in whom five custom-made peritoneal catheters were used over a 3-year period. There were two males and the mean age was 10 years (6 months-17 years). In all patients, placement of an EVD was necessary for sub-zero drainage, with maximum negative pressure of -8 cm H20. The mean time of maintenance of EVD was 102 days (10 days-1 year). Finally, three ventriculoperitoneal (VP) valveless systems, one with antigravitation device, and one Pro-GAV VP shunt were placed, all of them with larger custom-made peritoneal catheters. After a mean follow-up period of 2.3 years (6 months-3 years), two patients are completely recovered, one patient is partially dependent for daily activities with good cognitive status, and the last one is a child who died due to his brain tumor.
CONCLUSION: The custom-made peritoneal catheters with larger inner diameter could be a good option for the management of this complex pathology.

"Compensated Hyperosmolarity" Of Cerebrospinal Fluid And The Development Of Hydrocephalus

Authors: Klarica M, Miše B, Vladić A, Radoš M, Orešković D.

Acute osmolar loading of cerebrospinal fluid within one lateral ventricle of dogs was examined as a cause of water extraction from the bloodstream and an increase in intracranial pressure. We have shown that a certain amount of 3H2O from the bloodstream enters osmotically loaded cerebrospinal fluid significantly faster, hence causing a significant increase in intracranial pressure. The noted phenomenon in which intracranial pressure still significantly increases, but in which the hyperosmolarity of the cerebrospinal fluid is no longer present, was named "compensated hyperosmolarity". In the case of the sub-chronic application of hyperosmolar solutions into cat ventricles, we observed an increase in cerebrospinal fluid volume and a more pronounced development of hydrocephalus in the area of application, but without significant increase in intracranial pressure and without blockage of cerebrospinal fluid pathways. These results support the newly proposed hypothesis of cerebrospinal fluid hydrodynamics and the ability to develop new strategies for the treatment of cerebrospinal fluid-related diseases.

Hypothesis for intracranial hypertension in slit ventricle syndrome: New concept of capillary absorption laziness in the hydrocephalic patients with long-term shunts

Authors: Jang M, Yoon SH.

Many theories have been postulated to date regarding mechanisms involved in intracranial hypertension in patients with long-term, shunt-induced slit ventricle syndrome (SVS), but it still seems difficult to define this entity more clearly. Many hypotheses have attempted to explain the causes of SVS as chronic or intermittent catheter obstruction, brain compliance change, and ventricular herniation and distortion, but this theory does not explain clearly the reason why extraventricular pressure (EVP) is increased and intraventricular pressure (IVP) is low or frequently negative. The authors attempt to postulate a hypothesis by addressing new concept of capillary absorption laziness which results in dissociation of EVP with IVP. We, the authors, propose a concept of 'capillary absorption laziness', which is a tendency of the brain parenchymal extracellular fluid (ECF) not to be absorbed through the brain parenchymal capillary absorption system (BPCAS) that results from the bypass of ECF to shunt in the low or even negative ECF pressure and IVP. If this continues for a prolonged period, the tendency not to be absorbed through the BPCAS, even when the IVP and extracellular fluid pressures increases more than the intracranial pressure (ICP), may be established. This leads to situations of the brain such as parenchymal accumulation of the ECF which results in brain edema or swelling, and eventually distortion or herniation which can act as a functional obstruction and consequent dissociation between the IVP and EVP. Hypothesis of capillary absorption laziness may explain several common phenomena of the SVS such as low or even negative IVP in coexistence with high EVP and high ICP, and in these cases, we expect serious complications of SVS such as brain distortion and herniation. From this hypothesis we attempt to find new shunt management protocols to prevent long-term shunt induced complications.


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