Osmotherapy in neurocritical care

Computational modelling of cerebral oedema and osmotherapy following ischaemic stroke

In ischaemic stroke, a large reduction in blood supply can lead to the breakdown of the blood brain barrier and to cerebral oedema after reperfusion therapy. Cerebral oedema is marked by elevated intracranial pressure (ICP), tissue herniation and reduced cerebral perfusion pressure. In clinical settings, osmotherapy has been a common practice to decrease ICP. However, there are no guidelines on the choice of administration protocol parameters such as injection doses, infusion time and retention time. Most importantly, the effects of osmotherapy have been proven controversial since the infusion of osmotic agents can lead to a range of side effects. Here, a new Finite Element model of brain oedema and osmotherapy is thus proposed to predict treatment outcome. The model consists of three components that simulate blood perfusion, oedema, and osmotherapy, respectively. In the perfusion model (comprising arteriolar, venous, and capillary blood compartments), an anatomically accurate brain geometry is used to identify regions with a perfusion reduction and potential oedema occurrence in stroke. The oedema model is then used to predict ICP using a porous circulation model with four fluid compartments (arteriolar blood, venular blood, capillary blood, and interstitial fluid). In the osmotherapy model, the osmotic pressure is varied and the changes in ICP during different osmotherapy episodes are quantified. The simulation results of the model show excellent agreement with available clinical data and the model is employed to study osmotherapy under various parameters. Consequently, it is demonstrated how therapeutic strategies can be proposed for patients with different pathological parameters based on simulations.

Synovial Fluid of Patient With Rheumatoid Arthritis Enhanced Osmotic Sensitivity Through the Cytotoxic Edema Module in Synoviocytes

Rheumatoid arthritis (RA) is an autoimmune disease that causes inflammation of the synovial membrane ultimately leading to permanent damage in the affected joints. For this study, synovial fluids from 16 patients diagnosed with either RA or osteoarthritis (OA) were used to examine volume regulation and cooperative water channels, both of which are involved in the cytotoxic edema identified in RA-fibroblast-like synoviocytes (FLS). The osmolarity and inflammatory cytokine interleukin (IL)-6 of synovial fluids from RA patients were mildly enhanced compared to that from OA patients. RA-FLS demonstrated the enhanced property of regulatory volume increase in response to IL-6 and synovial fluids from RA patients. Although there was no difference in the protein expression of the volume-associated protein sodium–potassium–chloride cotransporter1 (NKCC1), its activity was increased by treatment with IL-6. Membrane localization of NKCC1 was also increased by IL-6 treatment. Additionally, both the protein and membrane expressions of aquaporin-1 were increased in RA-FLS by IL-6 stimulation. The IL-6-mediated enhanced osmotic sensitivity of RA-FLS likely involves NKCC1 and aquaporin-1, which mainly constitute the volume-associated ion transporter and water channel elements. These results suggest that RA-FLS provide enhanced electrolytes and concomitant water movement through NKCC1 and aquaporin-1, thereby inducing cellular swelling ultimately resulting in cytotoxic edema. Attenuation of cytotoxic edema and verification of its related mechanism will provide novel therapeutic approaches to RA treatment within the scope of cytotoxic edema.

Potentially Detrimental Effects of Hyperosmolality in Patients Treated for Traumatic Brain Injury

Hyperosmotic therapy is commonly used to treat intracranial hypertension in traumatic brain injury patients. Unfortunately, hyperosmolality also affects other organs. An increase in plasma osmolality may impair kidney, cardiac, and immune function, and increase blood–brain barrier permeability. These effects are related not only to the type of hyperosmotic agents, but also to the level of hyperosmolality. The commonly recommended osmolality of 320 mOsm/kg H₂O seems to be the maximum level, although an increase in plasma osmolality above 310 mOsm/kg H₂O may already induce cardiac and immune system disorders. The present review focuses on the adverse effects of hyperosmolality on the function of various organs.

Hyperosmolar therapy: A century of treating cerebral edema

Hyperosmolar therapy is a cornerstone for the management of elevated intracranial pressure in patients with devastating neurological injuries. Its discovery and use in various pathologies has become a valuable therapy in modern neurological critical care across the globe. Although hyperosmolar therapy is used routinely, the history of its origin is still elusive to many physicians. Understanding the basis of discovery and use of different hyperosmolar agents lends insight into the complex management of elevated intracranial pressure. There are very few practices in medicine which has stood the test of time. The discovery of hyperosmolar therapy has not only provided us a wealth of data for the management of intracranial hypertension but has also allowed us to develop new treatment strategies by improving our understanding of the molecular mechanisms of cerebral inflammation, blood-brain permeability, and cerebral edema in all modes of neuronal injury.

What is the Role of Hyperosmolar Therapy in Hemispheric Stroke Patients?

The role of hyperosmolar therapy (HT) in large hemispheric ischemic or hemorrhagic strokes remains a controversial issue. Past and current stroke guidelines state that it represents a reasonable therapeutic measure for patients with either neurological deterioration or intracranial pressure (ICP) elevations documented by ICP monitoring. However, the lack of evidence for a clear effect of this therapy on radiological tissue shifts and clinical outcomes produces uncertainty with respect to the appropriateness of its implementation and duration in the context of radiological mass effect without clinical correlates of neurological decline or documented elevated ICP. In addition, limited data suggest a theoretical potential for harm from the prophylactic and protracted use of HT in the setting of large hemispheric lesions. HT exerts effects on parenchymal volume, cerebral blood volume and cerebral perfusion pressure which may ameliorate global ICP elevation and cerebral blood flow; nevertheless, it also holds theoretical potential for aggravating tissue shifts promoted by significant interhemispheric ICP gradients that may arise in the setting of a large unilateral supratentorial mass lesion. The purpose of this article is to review the literature in order to shed light on the effects of HT on brain tissue shifts and clinical outcome in the context of large hemispheric strokes, as well as elucidate when HT should be initiated and when it should be avoided.

Hyperosmolar Treatment for Patients at Risk for Increased Intracranial Pressure: A Single-Center Cohort Study

Treatment with osmoactive agents such as mannitol or hypertonic saline (HTS) solutions is widely used to manage or prevent the increase of intracranial pressure (ICP) in central nervous system (CNS) disorders. We sought to evaluate the variability and mean plasma concentrations of the water and electrolyte balance parameters in critically ill patients treated with osmotic therapy and their influence on mortality. This cohort study covered patients hospitalized in an intensive care unit (ICU) from January 2017 to June 2019 with presumed increased ICP or considered to be at risk of it, treated with 15% mannitol (G1, n = 27), a combination of 15% mannitol and 10% hypertonic saline (HTS) (G2, n = 33) or 10% HTS only (G3, n = 13). Coefficients of variation (Cv) and arithmetic means (mean) were calculated for the parameters reflecting the water and electrolyte balance, i.e., sodium (NaCv/NaMean), chloride (ClCv/ClMean) and osmolality (mOsmCv/mOsmMean). In-hospital mortality was also analyzed. The study group comprised 73 individuals (36 men, 49%). Mortality was 67% (n = 49). Median NaCv (G1: p = 0.002, G3: p = 0.03), ClCv (G1: p = 0.02, G3: p = 0.04) and mOsmCv (G1: p = 0.001, G3: p = 0.02) were higher in deceased patients. NaMean (p = 0.004), ClMean (p = 0.04), mOsmMean (p = 0.003) were higher in deceased patients in G3. In G1: NaCv (AUC = 0.929, p < 0.0001), ClCv (AUC = 0.817, p = 0.0005), mOsmCv (AUC = 0.937, p < 0.0001) and in G3: NaMean (AUC = 0.976, p < 0.001), mOsmCv (AUC = 0.881, p = 0.002), mOsmMean (AUC = 1.00, p < 0.001) were the best predictors of mortality. The overall mortality prediction for combined G1+G2+G3 was very good, with AUC = 0.886 (p = 0.0002). The mortality of critically ill patients treated with osmotic agents is high. Electrolyte disequilibrium is the independent predictor of mortality regardless of the treatment method used. Variations of plasma sodium, chloride and osmolality are the most deleterious factors regardless of the absolute values of these parameters.

Effects of Conivaptan versus Mannitol on Post-Ischemic Brain Injury and Edema

Objective

The aim of this study was to compare the effects of conivaptan, an arginine vasopressin antagonist, and mannitol, a sugar alcohol, on cerebral ischemia-induced brain injury and edema in rats.

Materials and Methods

Fifty-eight 8-week-old male Sprague Dawley rats were randomly divided into five groups: control, ischemia-reperfusion (I/R)+saline, I/R+mannitol, I/R+10 mg/ml conivaptan, and I/R+20 mg/ml conivaptan. Cerebral ischemia was induced by common carotid artery occlusion for 30 minutes. Saline, mannitol, or conivaptan were administered intravenously at the onset of reperfusion. Blood and brain tissue samples were taken at the 6th hour of reperfusion. The electrolytes (Na+-K+-Cl-), osmolality, arginine vasopressin, albumin, progranulin (PGRN), neuron-specific enolase (NSE), and myeloperoxidase activity were measured in rat serum samples. Brain frontal/hippocampal sections were stained with hematoxylin-eosin and TUNEL techniques to evaluate histopathological changes.

Results

Statistical analyses revealed that conivaptan caused significant changes in the electrolyte, NSE, and PGRN levels and osmolality when compared with mannitol. Conivaptan treatment showed positive effects on serum biochemistry and tissue histology.

Conclusion

Our findings revealed that conivaptan shows more diuretic activity than mannitol and triggers neither any damages nor edema in the brain tissue. This study may provide beneficial information for the development of treatment strategies for ischemia-related cerebrovascular diseases.

Evaluation of the Maintained Effect of 3% Hypertonic Saline Solution in an Animal Model of Intracranial Hypertension

Background

Current clinical treatment methods for refractory intracranial hypertension include elevation of the decubitus, ventilation adjustment, and use of hypertonic solutions such as hypertonic saline and mannitol solutions. Previous studies have shown that hypertonic solutions are particularly effective. Although several concentrations of saline solution have been proposed, a 3% solution is the most widely used. The aim of this study was to evaluate the maintained efficacy of a 3% hypertonic saline solution in an experimental model of intracranial hypertension.

Material/Methods

A porcine model of reversible intracranial hypertension was created by inserting a balloon catheter into the brain parenchyma, which was inflated and deflated to simulate intracranial hypertension and its surgical correction. The experiment included 3 groups of animals (A, B, and C) with different balloon inflation volumes. In group B, balloons were inflated 2 times to simulate reexpansion. A 20 mL/kg bolus of 3% saline solution was infused using a pump 90 minutes after the start of balloon inflation, and the effects of intracranial pressure were evaluated 60 minutes after infusion.

Results

No increases outside of the normal range were observed in mean serum sodium concentrations (p=0.09). In addition, we identified no differences within each group in serum sodium levels measured during hypertonic saline infusion (p=0.21). No significant reductions in intracranial pressure were observed in any of the 3 groups.

Conclusions

Bolus infusion of 3% hypertonic saline solution with the aid of a pump does not significantly reduce intracranial pressure in an animal model of intracranial hypertension.

A prospective randomized trial of the optimal dose of mannitol for intraoperative brain relaxation in patients undergoing craniotomy for supratentorial brain tumor resection

OBJECTIVE

Mannitol is used intraoperatively to induce brain relaxation in patients undergoing supratentorial brain tumor resection. The authors sought to determine the dose of mannitol that provides adequate brain relaxation with the fewest adverse effects.

METHODS

A total of 124 patients were randomized to receive mannitol at 0.25 g/kg (Group A), 0.5 g/kg (Group B), 1.0 g/kg (Group C), and 1.5 g/kg (Group D). The degree of brain relaxation was classified according to a 4-point scale (1, bulging; 2, firm; 3, adequate; and 4, perfectly relaxed) by neurosurgeons; Classes 3 and 4 were considered to indicate satisfactory brain relaxation. The osmolality gap (OG) and serum electrolytes were measured before and after mannitol administration.

RESULTS

The brain relaxation score showed an increasing trend in patients receiving higher doses of mannitol (p = 0.005). The incidence of satisfactory brain relaxation was higher in Groups C and D than in Group A (67.7% and 64.5% vs 32.2%, p = 0.011 and 0.022, respectively). The incidence of OG greater than 10 mOsm/kg was also higher in Groups C and D than in Group A (100.0% in both groups vs 77.4%, p = 0.011 for both). The incidence of moderate hyponatremia (125 mmol/L ≤ Na+ < 130 mmol/L) was significantly higher in Group D than in other groups (38.7% vs 0.0%, 9.7%, and 12.9% in Groups A, B, and C; p < 0.001, p = 0.008, and p = 0.020, respectively). Hyperkalemia (K+ > 5.0 mmol/L) was observed in 12.9% of patients in Group D only.

CONCLUSIONS

The higher doses of mannitol provided better brain relaxation but were associated with more adverse effects. Considering the balance between the benefits and risks of mannitol, the authors suggest the use of 1.0 g/kg of intraoperative mannitol for satisfactory brain relaxation with the fewest adverse effects.

Clinical trial registration no.: NCT02168075 (clinicaltrials.gov)

Mechanics of the brain: perspectives, challenges, and opportunities

The human brain is the continuous subject of extensive investigation aimed at understanding its behavior and function. Despite a clear evidence that mechanical factors play an important role in regulating brain activity, current research efforts focus mainly on the biochemical or electrophysiological activity of the brain. Here, we show that classical mechanical concepts including deformations, stretch, strain, strain rate, pressure, and stress play a crucial role in modulating both brain form and brain function. This opinion piece synthesizes expertise in applied mathematics, solid and fluid mechanics, biomechanics, experimentation, material sciences, neuropathology, and neurosurgery to address today’s open questions at the forefront of neuromechanics. We critically review the current literature and discuss challenges related to neurodevelopment, cerebral edema, lissencephaly, polymicrogyria, hydrocephaly, craniectomy, spinal cord injury, tumor growth, traumatic brain injury, and shaken baby syndrome. The multi-disciplinary analysis of these various phenomena and pathologies presents new opportunities and suggests that mechanical modeling is a central tool to bridge the scales by synthesizing information from the molecular via the cellular and tissue all the way to the organ level.

The history of urea as a hyperosmolar agent to decrease brain swelling

In 1919, it was observed that intravascular osmolar shifts could collapse the thecal sac and diminish the ability to withdraw CSF from the lumbar cistern. This led to the notion that hyperosmolar compounds could ameliorate brain swelling. Since then, various therapeutic interventions have been used for the reduction of intracranial pressure and brain volume.

Urea was first used as an osmotic agent for the reduction of brain volume in 1950. It was associated with greater efficacy and consistency than alternatives such as hyperosmolar glucose. Its use became the standard of clinical practice by 1957, in both the intensive care unit and operating room, to reduce intracranial pressure and brain bulk and was the first hyperosmolar compound to have widespread use. However, the prime of urea was rather short lived. Reports of side effects and complications associated with urea emerged. These included coagulopathy, hemoglobinuria, electrocardiography changes, tissue necrosis with extravasation, and a significant potential for rebound intracranial hypertension.

Mannitol was introduced in 1961 as a comparable and potentially superior alternative to urea. However, mannitol was initially purported to be less effective at rapidly reducing intracranial pressure. The debate over the two compounds continued for a decade until mannitol eventually replaced urea by the late 1960s and early 1970s as the hyperosmolar agent of choice due to the ease of preparation, chemical stability, and decreased side effect profile.

Although urea is not currently the standard of care today, its rise and eventual replacement by mannitol played a seminal role in both our understanding of cerebral edema and the establishment of strategies for its management.

Osmotherapy in brain edema: a questionable therapy

Despite the fact that it has been used since the 1960s in diseases associated with brain edema and has been investigated in >150 publications on head injury, very little has been published on the outcome of osmotherapy. We can only speculate whether osmotherapy improves outcome, has no effect on outcome, or leads to worse outcome. Here we describe the action and potentially beneficial and adverse effects of the 2 most commonly used osmotic solutions, mannitol and hypertonic saline, and present some critical aspects of their use. There is a well-documented transient intracranial pressure (ICP)-reducing effect of osmotherapy, but an adverse rebound increase in ICP after its withdrawal has been discussed extensively in the literature and is an expected pathophysiological phenomenon. From side effects related to renal and pulmonary failure, electrolyte disturbances, and a rebound increase in ICP, osmotherapy can be negative for outcome, which may explain why we lack scientific support for its use. These drawbacks, and the fact that the most recent Cochrane meta-analyses of osmotherapy in brain edema and stroke could not find any beneficial effects on outcome, make routine use of osmotherapy in brain edema doubtful. Nevertheless, the use of osmotherapy as a temporary measure may be justified to acutely prevent brain stem compression until other measures, such as evacuation of space-occupying lesions or decompressive craniotomy, can be performed. This article is the Con part in a Pro-Con debate in the present journal on the general routine use of osmotherapy in brain edema.

Osmotherapy for intracranial hypertension: mannitol versus hypertonic saline

PURPOSE OF REVIEW

Hyperosmolar therapy is one of the core medical treatments for brain edema and intracranial hypertension, but controversy exists regarding the use of the most common agents, mannitol, and hypertonic saline. This article describes the relative merits and adverse effects of these agents using the best available clinical evidence.

RECENT FINDINGS

Mannitol is effective and has been used for decades in the treatment of traumatic brain injury, but it may precipitate acute renal failure if serum osmolarity exceeds 320 mOsm/L. Hypertonic saline appears to be safe, and serum sodium has been elevated to as high as 180 mEq/L in clinical settings without significant neurologic, cardiac, or renal injury. In small comparative trials both agents are effective and no clinically significant difference has been noted, but a properly powered trial has not yet been performed.

SUMMARY

Both mannitol and hypertonic saline are effective and have an acceptable risk profile for use in the treatment of elevated intracranial pressure secondary to brain edema.

Medical care of patients with brain tumors

PURPOSE OF REVIEW

Patients with brain tumors require close attention to medical issues resulting from their disease or its therapy. Effective medical management results in decreased morbidity and mortality and improved quality of life. The most frequent neurology-related issues that arise in these patients include seizures, peritumoral edema, venous thromboembolism, fatigue, and cognitive dysfunction. This article focuses on the most recent findings for the management of the most relevant medical complications among patients with brain tumors.

RECENT FINDINGS

Increasing evidence suggests that anticoagulation in patients with thromboembolic complications is safe even when they are receiving antiangiogenic therapy. There are also increasing data to support the use of newer, non-enzyme-inducing antiepileptic drugs, which have the advantage of lacking interactions with antineoplastic agents and are as effective as their older counterparts at preventing seizures. Relatively few studies have addressed the management of fatigue and depression, and definitive recommendations cannot be made.

SUMMARY

Corticosteroids to treat vasogenic edema should be used at the minimum amount required to control symptoms and should be tapered as quickly as possible. Anticonvulsants should be used only if patients have had seizures. Non-enzyme-inducing antiepileptic drugs are preferred to minimize interactions with concurrently administered chemotherapy. Thromboembolic complications are common and are preferably treated with low-molecular-weight heparins. Only patients with hemorrhagic complications require an inferior vena cava filter. Cognitive deficits are frequent in patients with brain tumors and include problems such as poor short-term memory, distractibility, personality change, emotional lability, loss of executive function, and decreased psychomotor speed. Stimulants can help to improve these symptoms.

Topical mannitol reduces inflammatory edema in a rat model of arthritis

The hexahydric alcohol mannitol is widely used to shift fluids from the intracellular to the extracellular compartments, to increase diuresis and improve mucus clearance in the airways. In principle, because of its physicochemical properties, topical mannitol might also draw fluids out of epidermis or mucosa. Here, we report that topical mannitol applications on the hind paws of rats with adjuvant-induced arthritis reduced paw thickness and tissue edema without affecting the inflammatory infiltrates. Of note, the anti-edema effects of acute (4 h) mannitol application occurred earlier than those prompted by a similar treatment with classic anti-inflammatory drugs such as diclofenac or ketoprofen. Yet, the extent of edema reduction was higher with diclofenac or ketoprofen than with mannitol when the drugs were applied in a chronic (16 h) paradigm. Together, data demonstrate that topical application of mannitol exerts potent and fast anti-edema effects in a rat model of joint inflammation, suggesting a possible utilization in patients affected by osseo-arthritic disorders.

Osmotherapy: use among neurointensivists

BACKGROUND

Cerebral edema and raised intracranial pressure are common problems in neurological intensive care. Osmotherapy, typically using mannitol or hypertonic saline (HTS), has become one of the first-line interventions. However, the literature on the use of these agents is heterogeneous and lacking in class I studies. The authors hypothesized that clinical practice would reflect this heterogeneity with respect to choice of agent, dosing strategy, and methods for monitoring therapy.

METHODS

An on-line survey was administered by e-mail to members of the Neurocritical Care Society. Multiple-choice questions regarding use of mannitol and HTS were employed to gain insight into clinician practices.

RESULTS

A total of 295 responses were received, 79.7% of which were from physicians. The majority (89.9%) reported using osmotherapy as needed for intracranial hypertension, though a minority reported initiating treatment prophylactically. Practitioners were fairly evenly split between those who preferred HTS (54.9%) and those who preferred mannitol (45.1%), with some respondents reserving HTS for patients with refractory intracranial hypertension. Respondents who preferred HTS were more likely to endorse prophylactic administration. Preferred dosing regimens for both agents varied considerably, as did monitoring parameters.

CONCLUSIONS

Treatment of cerebral edema using osmotically active substances varies considerably between practitioners. This variation could hamper efforts to design and implement multicenter trials in neurocritical care.

Na(+)-K (+)-2Cl (-) cotransport inhibitor attenuates cerebral edema following experimental stroke via the perivascular pool of aquaporin-4

INTRODUCTION

The Na(+)-K(+)-2Cl(-) cotransporter localized in the brain vascular endothelium has been shown to be important in the evolution of cerebral edema following experimental stroke. Previous in vivo studies have demonstrated that bumetanide, a selective Na(+)-K(+)-2Cl(-) cotransport inhibitor, attenuates ischemia-evoked cerebral edema. Recently, bumetanide has been shown to also inhibit water permeability via aquaporin-4 (AQP4) expressed in Xenopus laevis oocytes. We tested the hypothesis that the perivascular pool of AQP4 plays a significant role in the anti-edema effect of bumetanide by utilizing wild-type (WT) mice as well as mice with targeted disruption of alpha-syntrophin (alpha-Syn(-/-)) that lack the perivascular pool of AQP4.

METHODS

Isoflurane-anesthetized adult male WT C57Bl6 and alpha-Syn(-/-) mice were subjected to 90 min middle cerebral artery occlusion (MCAO) followed by 24 or 48 h of reperfusion. Adequacy of MCAO and reperfusion was monitored with laser-Doppler flowmetry over the ipsilateral parietal cortex. Infarct volume (tetrazolium staining), cerebral edema (wet-to-dry ratios), and AQP4 protein expression (immunoblotting) were determined in different treatment groups in separate sets of experiments.

RESULTS

Bumetanide significantly attenuated infarct volume and decreased ipsilateral hemispheric water content in WT mice compared to vehicle treatment. In alpha-Syn(-/-) mice, bumetanide treatment had no effect on infarct volume or ischemia-evoked cerebral edema. Bumetanide-treated WT mice had a significant attenuation of AQP4 protein expression at 48 h post-MCAO compared to vehicle-treated WT mice.

CONCLUSIONS

These data suggest that bumetanide exerts its neuroprotective and anti-edema effects partly via blockade of the perivascular pool of AQP4 and may have therapeutic potential for ischemic stroke in the clinical setting.

Fixed negative charge and the Donnan effect: a description of the driving forces associated with brain tissue swelling and oedema

Cerebral oedema or brain tissue swelling is a significant complication following traumatic brain injury or stroke that can increase the intracranial pressure (ICP) and impair blood flow. Here, we have identified a potential driver of oedema: the negatively charged molecules fixed within cells. This fixed charge density (FCD), once exposed, could increase ICP through the Donnan effect. We have shown that metabolic processes and membrane integrity are required for concealing this FCD as slices of rat cortex swelled immediately (within 30 min) following dissection if treated with 2 deoxyglucose + cyanide (2DG+CN) or Triton X-100. Slices given ample oxygen and glucose, however, did not swell significantly. We also found that dead brain tissue swells and shrinks in response to changes in ionic strength of the bathing medium, which suggests that the Donnan effect is capable of pressurizing and swelling brain tissue. As predicted, a non-ionic osmolyte, 1,2 propanediol, elicited no volume change at 2000 x 10(-3) osmoles l(-1) (Osm). Swelling data were well described by triphasic mixture theory with the calculated reference state FCD similar to that measured with a 1,9 dimethylmethylene blue assay. Taken together, these data suggest that intracellular fixed charges may contribute to the driving forces responsible for brain swelling.

Cryptococcus neoformans responds to mannitol by increasing capsule size in vitro and in vivo

The polysaccharide capsule of the fungus Cryptococcus neoformans is its main virulence factor. In this study, we determined the effects of mannitol and glucose on the capsule and exopolysaccharide production. Growth in mannitol significantly increased capsular volume compared with cultivation in glucose. However, cells grown in glucose concentrations higher than 62.5 mM produced more exopolysaccharide than cells grown in mannitol. The fibre lengths and glycosyl composition of capsular polysaccharide from yeast grown in mannitol was structurally different from that of yeast grown in glucose. Furthermore, mannitol treatment of mice infected intratracheally with C. neoformans resulted in fungal cells with significantly larger capsules and the mice had reduced fungal dissemination to the brain. Our results demonstrate the capacity of carbohydrate source and concentration to modify the expression of a major virulence factor of C. neoformans. These findings may impact the clinical management of cryptococcosis.

Management of intracranial pressure

Although intracranial hypertension may arise from diverse pathology, several basic principles remain paramount to understanding its dynamics; however, the management of elevated intracranial pressure (ICP) may be very complex. Initial management of common ICP exacerbants is important, such as addressing venous outflow obstruction with upright midline head positioning and treating agitation and pain with sedation and analgesia. Surgical decompression of mass effect may rapidly improve ICP elevation, but the impact on outcome is unclear. Considerable effort has been put forth to understand the roles of multimodal intensive care monitoring, osmolar therapy, cerebral metabolic suppression, and temperature augmentation in the advanced management of elevated ICP. Establishing a protocol-driven approach to the management of ICP enables the rapid bedside assessment of multiple physiologic variables to implement appropriate treatments, which limit the risk of developing secondary brain injury.