Effect of hydration status on cerebral blood flow and cerebrospinal fluid lactic acidosis in rabbits with experimental meningitis

Neuroprotective effects of CysLTR antagonist on Streptococcus pneumoniae‑induced meningitis in rats

Cysteinyl leukotrienes (CysLTs) modulate central nervous system inflammatory responses via their receptors, CysLT₁R and CysLT₂R. It has been demonstrated that CysLTR participates in the infection process of Streptococcus pneumoniae (SP)-induced meningitis. In the present study, the effects and possible underlying mechanisms of CysLTR antagonists (pranlukast and HAMI 3379) on SP meningitis were further determined. SP meningitis was induced by intracerebroventricular injection of serotype III SP in Sprague-Dawley rats which were administrated intraperitoneally with 0.1 mg/kg antagonists. The clinical disease status of rats was evaluated by body weight and behavioral changes with neurological scoring. Survival neuron density, activated microglial and astrocytes were assessed by Nissl staining and immunohistochemical staining. The expression levels of inflammatory cytokines and NLRP3 inflammasome were detected by reverse transcription-quantitative PCR and western blotting, respectively. Pranlukast and HAMI 3379 treatment markedly alleviated the clinical disease status, which was manifested by improving body weight loss and neurological deficit. Furthermore, pranlukast and HAMI 3379 treatment ameliorated neuronal injury and inhibited microgliosis and astrogliosis. In addition, significant downregulation of inflammatory cytokines and NLRP3 expression was observed in pranlukast and HAMI 3379-treated rats. These in vivo findings indicated the neuroprotective effects of CysLTR antagonists against experimental SP-induced meningitis, and the mechanism of anti-inflammatory effects may partly be by inhibiting NLRP3 inflammasome overactivation.

Expression of cysteinyl leukotriene receptor in brain tissues of rats with Streptococcus pneumoniae meningitis

Streptococcus pneumoniae meningitis is an infection of the central nervous system associated with high mortality rates and serious neurologic sequelae in children. The principal reason for the severity of S. pneumoniae meningitis is widespread ignorance of the pathogenesis of the disease. This study aimed at exploring whether cysteinyl leukotriene receptor (CysLTR) participates in the inflammatory response and elucidates the pathologic process of S. pneumoniae meningitis. Bacterial meningitis disease models were constructed by intracisternal inoculation of rats with serotype III Streptococcus pneumoniae while control models were inoculated with the same volume of normal saline. Rats were sacrificed at different time points (1 d, 2 d, and 5 d) following the administration of Streptococcus pneumoniae. Results from the body-weight, Loeffler neurologic deficit score, and cerebrospinal fluid culture confirmed that a successful pneumococcal meningitis rat model was established. Pathologic changes in brain tissues mainly consisted of inflammation in the meninges and subarachnoid space and significant neuronal injury in the cerebral cortex and hippocampus (P < 0.05). Immunohistochemical analysis revealed that microglial activation and astrocyte proliferation were associated with the development of bacterial meningitis. The expression levels of CysLTR and inflammatory factor tumor necrosis factor-α (TNF-α) were examined by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot analysis. The results of this study indicate that CysLTR expression was markedly elevated in the 5 d infection group (P < 0.05), which was consistent with time-dependent release of TNF-α. The findings of this study indicate that CysLTR participates in the pneumococcal meningitis infection process by mediating neuronal injury and glial cell proliferation. Cysteinyl leukotriene receptors could, therefore, be novel targets to mitigate the progression of pneumococcal meningitis.

Establishment of rat pneumococcal meningitis models: a histopathological analysis

The aim of this study was to perform a preliminary investigation of the pathogenesis of bacterial meningitis-induced brain injury by establishing rat pneumococcal meningitis models. Infant Wistar rats were intracranially inoculated with different concentrations of Streptococcus pneumoniae. Rats were sacrificed at different time points to observe clinical symptoms and pathological changes in brain tissues. Twenty-four hours after intracranial inoculation with Streptococcus pneumoniae, regardless of high or low concentrations of bacterial inoculation, all rats developed bacterial meningitis with manifestations such as lethargy and seizures. Pathological changes in brain tissues included subarachnoid and intraventricular inflammation, vasodilation and vascular congestion, and cortical neuronal necrosis. The number of rats with seizures, the degree of cerebral vascular disease, and the extent of neuronal damage were associated with the concentration of bacterial inoculum. Thirty days after infection, brain tissue weight significantly reduced. The pathological changes induced by inoculation with pneumococcal meningitis in Wistar rats were similar to those seen in the human brain. The possible mechanisms of brain damage caused by meningitis are cerebrovascular inflammation and disruption of regional cerebral blood flow.

Bacterial meningitis: new therapeutic approaches

Bacterial meningitis remains a disease with high mortality and long-term morbidity. Outcome critically depends on the rapid initiation of effective antibiotic therapy. Since a further increase of the incidence of pathogens resistant to antibacterials can be expected both in community-acquired and nosocomial bacterial meningitis, the choice of an optimum initial empirical antibiotic regimen will gain significance. In this context, the use of antibiotics which are bactericidal but do not lyse bacteria, may emerge as a therapeutic option. Conversely, the role of corticosteroids, which decrease the entry of hydrophilic antibacterials into the cerebrospinal fluid, as adjunctive therapy will probably decline as a consequence of the increasing antibiotic resistance of bacteria causing meningitis. Consequent vaccination of all children at present is the most efficient manner to reduce disease burden.

Neurocritical care of patients with central nervous system infections

Bacterial meningitis and viral encephalitis are life-threatening infections with high mortality rates. Patients who survive these infections often remain permanently disabled. Potential neurologic complications requiring careful attention include impaired consciousness, elevated intracranial pressure (ICP), hydrocephalus, stroke, and seizures. Systemic complications are also common and are frequently the immediate cause of death. The importance of emergent administration of appropriate antimicrobial therapy cannot be overstated, but critical care of these patients should focus not only on treatment of the underlying infection and its immediate complications but also on minimizing secondary brain injury. Given the increasing complexity of the diagnostic and therapeutic modalities available to manage central nervous system (CNS) infections, the involvement of neurocritical care units and neurointensivists may be particularly helpful in improving outcomes. It is our opinion that ICP measurement should be strongly considered in selected patients with CNS infections, particularly those who are comatose. Treatments for intracranial hypertension, specifically in the setting of CNS infection, are described in this paper. For bacterial meningitis, intravenous dexamethasone should be administered, beginning concomitantly with the initial dose of antibiotics, at least until Streptococcus pneumoniae can be excluded as a pathogen. Clinicians should maintain a high index of suspicion for nonconvulsive seizures. Deterioration in neurologic status should also prompt early use of CT or magnetic resonance angiography and venography to exclude cerebrovascular complications.

Neurocritical care of patients with central nervous system infections

Bacterial meningitis and viral encephalitis are life-threatening infections with high mortality rates. Patients who survive these infections often remain permanently disabled. Potential neurologic complications requiring careful attention include impaired consciousness, elevated intracranial pressure, hydrocephalus, stroke, and seizures. Systemic complications are also common and are frequently the immediate cause of death. Critical care of these patients should focus not only on treatment of the underlying infection and its immediate complications but also on minimizing secondary brain injury. Given the increasing complexity of the diagnostic and therapeutic modalities available in managing central nervous system infections, the involvement of neurocritical care units and neurointensivists may be particularly helpful in improving outcomes.

[Adjunctive therapies (excluding corticosteroids). Site of initial management]

Bacterial meningitis is still a serious disease with a high risk of mortality and sequels. The progress in antibiotic treatment has not improved the prognosis. Thus, optimizing the initial care and the treatment of the most severe cases should improve the outcome. No study has compared the outcome according to the level of care at the admission site. There is evidence that the most severe cases should be managed by critical care units. It seems reasonable to recommend initial admission of common cases to units able to provide intensive care. Most people now agree that fluid restriction has not demonstrated its efficiency, furthermore it might have deleterious effects. However, a fluid overload should be avoided. Maintaining cerebral perfusion is a key issue in the treatment of bacterial meningitis and requires monitoring both arterial blood pressure and intracranial pressure. Intracranial pressure monitoring is probably useful to optimize the treatment of the most severe cases. The aggressive treatments of cerebral edema have not been evaluated but seem, in some limited series, able to improve some life threatening situations. The benefit of systematic glycerol administration needs confirmation. Seizures should be treated with the usual medications. However, drugs with potentially deleterious effects on hemodynamics should be avoided. There is no sufficient evidence to support the administration of a systematic prophylactic treatment. Fever should be treated when above 39.5 degrees C/40 degrees C and in the case of intracranial hypertension. There is no clinical study to explore the modifications of fever on bacterial growth or on inflammation as observed in some experimental studies.

The effect of S. pneumoniae bacteremia on cerebral blood flow autoregulation in rats

In the present study, we studied the effect of bacteremia on cerebral blood flow (CBF) autoregulation in a rat model of pneumococcal bacteremia and meningitis. Anesthetized rats were divided into five groups (A to E) and inoculated with pneumococci intravenously and normal saline intracisternally (group A, N=10); saline intravenously and pneumococci intracisternally (group B, N=10); pneumococci intravenously and pneumococci intracisternally (group C, N=5); saline intravenously, antipneumococcal antibody intravenously (to prevent bacteremia), and pneumococci intracisternally (group D, N=10); or saline intravenously and saline intracisternally (group E, N=10), respectively. Positive cultures occurred in the blood for all rats in groups A, B, and C, and in the cerebrospinal fluid for all rats in groups D and E. Twenty-four hours after inoculation, CBF was measured with laser-Doppler ultrasound during incremental reductions in cerebral perfusion pressure (CPP) by controlled hemorrhage. Autoregulation was preserved in all rats without meningitis (groups A and E) and was lost in 24 of 25 meningitis rats (groups B, C, and D) (P<0.01). In group A, the lower limit was higher than that of group E (P<0.05). The slope of the CBF/CPP regression line differed between the meningitis groups (P<0.001), being steeper for group B than groups C and D, with no difference between these two groups. The results suggest that pneumococcal bacteremia in rats triggers cerebral vasodilation, which right shifts the lower limit of, but does not entirely abolish, CBF autoregulation in the absence of meningitis, and which may further aggravate the vasoparalysis induced by concomitant pneumococcal meningitis.

Adjuvant glycerol and/or dexamethasone to improve the outcomes of childhood bacterial meningitis: a prospective, randomized, double-blind, placebo-controlled trial

BACKGROUND

Despite favorable meta-analyses, no study involving third-generation cephalosporins for the treatment of childhood bacterial meningitis has documented a benefit of adjuvant dexamethasone therapy if the outcomes are examined individually.

METHODS

We conducted a prospective, randomized, double-blind trial comparing adjuvant dexamethasone or glycerol with placebo in children aged from 2 months through 16 years in Latin America. Ceftriaxone was administered to all children; children were randomized to also receive dexamethasone intravenously, glycerol orally, both agents, or neither agent. Primary end points were death, severe neurological sequelae, or deafness, with the first 2 end points forming a composite end point. A subgroup analysis for Haemophilus influenzae type b meningitis was undertaken. Intention-to-treat analysis was performed using binary logistic regression models.

RESULTS

H. influenzae type b, pneumococci, and meningococci were the main agents found among 654 patients; dexamethasone was given to 166, dexamethasone and glycerol were given to 159, glycerol was given to 166, and placebo was given to 163. No adjuvant therapy significantly affected death or deafness. In contrast, glycerol and dexamethasone plus glycerol reduced severe neurological sequelae, compared with placebo; the odds ratios were 0.31 (95% confidence interval [95% CI], 0.13-0.76; P=.010) and 0.39 (95% CI, 0.17-0.93; P=.033), respectively. For neurological sequelae and death, the odds ratios were 0.44 (95% CI, 0.25-0.76; P=.003) and 0.55 (95% CI, 0.32-0.93; P=.027), respectively. Dexamethasone therapy prevented deafness in patients with H. influenzae type b meningitis only if patients were divided grossly into dexamethasone recipients and nonrecipients and if timing between dexamethasone and ceftriaxone administration was not taken into account (odds ratio, 0.27; 95% CI, 0.09-0.77; P=.014).

CONCLUSION

Oral glycerol therapy prevents severe neurological sequelae in patients with childhood meningitis. Safety, availability, low cost, and oral administration also add to its usefulness, especially in resource-limited settings.

Effects of hypertonic (7%) saline on brain injury in experimental Escherichia coli meningitis

We sought to know whether hypertonic (7%) saline (HTS) attenuates brain injury by improving cerebral perfusion pressure (CPP) and down-modulating acute inflammatory responses in experimental bacterial meningitis in the newborn piglet. Twenty-five newborn piglets were assorted into three groups: 6 in the control group (C), 10 in the meningitis group (M), and 9 in the meningitis with HTS infusion group (H). Meningitis was induced by intracisternal injection of 10(8) colony forming units of Escherichia coli in 100 microL of saline. 10 mL/kg of HTS was given intravenously as a bolus 6 hr after induction of meningitis, thereafter the infusion rate was adjusted to maintain the serum sodium level between 150 and 160 mEq/L. HTS significantly attenuated meningitis-induced brain cell membrane disintegration and dysfunction, as indicated by increased lipid peroxidation products and decreased Na+, K+-ATPase activity in the cerebral cortex in M. HTS significantly attenuated acute inflammatory markers such as increased intracranial pressure, elevated lactate level and pleocytosis in the cerebrospinal fluid observed in M. Reduced CPP observed in M was also significantly improved with HTS infusion. These findings implicate some attenuation of the meningitis-induced alterations in cerebral cortical cell membrane structure and function with HTS, possibly by improving CPP and attenuating acute inflammatory responses.

Reprogramming the host response in bacterial meningitis: how best to improve outcome?

Despite effective antibiotic therapy, bacterial meningitis is still associated with high morbidity and mortality in both children and adults. Animal studies have shown that the host inflammatory response induced by bacterial products in the subarachnoid space is associated with central nervous system injury. Thus, attenuation of inflammation early in the disease process might improve the outcome. The feasibility of such an approach is demonstrated by the reduction in neurologic sequelae achieved with adjuvant dexamethasone therapy. Increased understanding of the pathways of inflammation and neuronal damage has suggested rational new targets to modulate the host response in bacterial meningitis, but prediction of which agents would be optimal has been difficult. This review compares the future promise of benefit from the use of diverse adjuvant agents. It appears unlikely that inhibition of a single proinflammatory mediator will prove useful in clinical practice, but several avenues to reprogram a wider array of mediators simultaneously are encouraging. Particularly promising are efforts to adjust combinations of cytokines, to inhibit neuronal apoptosis and to enhance brain repair.

Controversies in the management of bacterial meningitis

Bacterial meningitis is an important infection of childhood with significant morbidity and mortality, and clinicians are faced with controversies over steroid use and fluid restriction in its initial management because the standard of practice is not clear. A 1999 survey of paediatric infectious diseases specialists demonstrated that only 56% of respondents recommended dexamethasone for Haemophilus influenzae type b meningitis and only 34% recommended dexamethasone for Streptococcus pneumoniae meningitis, despite recommendations for dexamethasone in the 1997 Red Book. The present article illustrates a typical case presentation of bacterial meningitis, and discusses dexamethasone use and fluid restriction. The use of intravenous fluid therapy is also reviewed, based on results from the single prospective randomized clinical trial in this area.

Bacterial meningitis in children: critical care needs

Acute bacterial meningitis (ABM) in children is associated with a high rate of acute complications and mortality, particularly in the developing countries. Most of the deaths occur during first 48 hours of hospitalization. Coma, raised intracranial pressure (ICP), seizures, shock have been identified as significant predictors of death and morbidity. This article reviews issues in critical care with reference to our experience of managing 88 children with ABM in PICU. Attention should first be directed toward basic ABCs of life-support. Children with Glasgow Coma Scale (GSC) score < 8 need intubation and supplemental oxygen. Antibiotics should be started, even without LP (contraindicated if focal neuro-deficit, papilledema, or signs of raised ICP). Raised ICP is present in most of patients; GCS < 8 and high blood pressure are good guides. Mannitol (0.25 gm/Kg) should be used in such patients. If there are signs of (impending) herniation short-term hyperventilation is recommended; prolonged hyperventilation (> 1 hour) must be avoided. Any evidence of poor perfusion, hypovolemia and/or hypotension needs aggressive treatment with normal saline boluses and inotropes, if necessary, to maintain normal blood pressure. Empiric fluid restriction is not justified. Seizures may be controlled with intravenous diazepam or lorazepam. Refractory status epilepticus may be treated with continuous diazepam (0.01-0.06) mg/kg/min) or midazolam infusion. Ventilatory support may be needed early for associated pneumonia, poor respiratory effort and/or coma, and occasionally to reduce work of breathing in shock. Provision of critical care to children with ABM may reduce the mortality significantly as experienced by us.

Regional cerebral blood flow during hyperventilation in patients with acute bacterial meningitis

Mechanical hyperventilation is often instituted in patients with acute bacterial meningitis when increased intracranial pressure is suspected. However, the effect on regional cerebral blood flow (CBF) is unknown. In this study, we measured regional CBF (rCBF) in patients with acute bacterial meningitis before and during short-term hyperventilation. In 17 patients with acute bacterial meningitis, absolute rCBF (in ml/100 g min-1) was measured during baseline ventilation and hyperventilation by single-photon emission computed tomography (SPECT) using intravenous 133Xe bolus injection. Intravenous 99mTc-HMPAO (hexamethylpropyleneamine oxime) was subsequently given during hyperventilation. In 12 healthy volunteers, rCBF was measured by SPECT and 99mTc-HMPAO during spontaneous ventilation. Using standard templates to identify regions of interest (ROIs), we calculated rCBF in percentage of cerebellar (99mTc-HMPAO images) or mean hemispheric (133Xe images) flow for each ROI, the degree of side-to-side asymmetry for each ROI, and the anterior-to-posterior flow ratio. On 133Xe images, absolute rCBF decreased significantly during hyperventilation compared to baseline ventilation in all regions, but the relative rCBF did not change significantly from baseline ventilation (n=14) to hyperventilation (n=12), indicating that the perfusion distribution was unchanged. On 99mTc-HMPAO images (n=12), relative rCBF and the anterior-to-posterior flow ratio were significantly lower in patients than in controls in the frontal and parietal cortex as well as in the basal ganglia. Focal perfusion abnormalities were present in 10 of 12 patients. Regional cerebral blood flow abnormalities are frequent in patients with acute bacterial meningitis. Short-term hyperventilation does not enhance these abnormalities.

Update on meningococcal disease with emphasis on pathogenesis and clinical management

The only natural reservoir of Neisseria meningitidis is the human nasopharyngeal mucosa. Depending on age, climate, country, socioeconomic status, and other factors, approximately 10% of the human population harbors meningococci in the nose. However, invasive disease is relatively rare, as it occurs only when the following conditions are fulfilled: (i) contact with a virulent strain, (ii) colonization by that strain, (iii) penetration of the bacterium through the mucosa, and (iv) survival and eventually outgrowth of the meningococcus in the bloodstream. When the meningococcus has reached the bloodstream and specific antibodies are absent, as is the case for young children or after introduction of a new strain in a population, the ultimate outgrowth depends on the efficacy of the innate immune response. Massive outgrowth leads within 12 h to fulminant meningococcal sepsis (FMS), characterized by high intravascular concentrations of endotoxin that set free high concentrations of proinflammatory mediators. These mediators belonging to the complement system, the contact system, the fibrinolytic system, and the cytokine system induce shock and diffuse intravascular coagulation. FMS can be fatal within 24 h, often before signs of meningitis have developed. In spite of the increasing possibilities for treatment in intensive care units, the mortality rate of FMS is still 30%. When the outgrowth of meningococci in the bloodstream is impeded, seeding of bacteria in the subarachnoidal compartment may lead to overt meningitis within 24 to 36 h. With appropriate antibiotics and good clinical surveillance, the mortality rate of this form of invasive disease is 1 to 2%. The overall mortality rate of meningococcal disease can only be reduced when patients without meningitis, i.e., those who may develop FMS, are recognized early. This means that the fundamental nature of the disease as a meningococcus septicemia deserves more attention.

Update on meningococcal disease with emphasis on pathogenesis and clinical management

The only natural reservoir of Neisseria meningitidis is the human nasopharyngeal mucosa. Depending on age, climate, country, socioeconomic status, and other factors, approximately 10% of the human population harbors meningococci in the nose. However, invasive disease is relatively rare, as it occurs only when the following conditions are fulfilled: (i) contact with a virulent strain, (ii) colonization by that strain, (iii) penetration of the bacterium through the mucosa, and (iv) survival and eventually outgrowth of the meningococcus in the bloodstream. When the meningococcus has reached the bloodstream and specific antibodies are absent, as is the case for young children or after introduction of a new strain in a population, the ultimate outgrowth depends on the efficacy of the innate immune response. Massive outgrowth leads within 12 h to fulminant meningococcal sepsis (FMS), characterized by high intravascular concentrations of endotoxin that set free high concentrations of proinflammatory mediators. These mediators belonging to the complement system, the contact system, the fibrinolytic system, and the cytokine system induce shock and diffuse intravascular coagulation. FMS can be fatal within 24 h, often before signs of meningitis have developed. In spite of the increasing possibilities for treatment in intensive care units, the mortality rate of FMS is still 30%. When the outgrowth of meningococci in the bloodstream is impeded, seeding of bacteria in the subarachnoidal compartment may lead to overt meningitis within 24 to 36 h. With appropriate antibiotics and good clinical surveillance, the mortality rate of this form of invasive disease is 1 to 2%. The overall mortality rate of meningococcal disease can only be reduced when patients without meningitis, i.e., those who may develop FMS, are recognized early. This means that the fundamental nature of the disease as a meningococcus septicemia deserves more attention.

Models of experimental bacterial meningitis. Role and limitations

The seriousness of bacterial meningitis has encouraged the development of animal models that characterize complex pathogenetic and pathophysiologic mechanisms, provide evaluation of pharmacokinetic and antimicrobial effects of antibiotics (especially since the worldwide emergence of multiresistant bacteria), and establish new adjuvant treatment strategies (e.g., use of anti-inflammatory agents). The information obtained from an animal model depends on the site of inoculation. For example, using intranasal, intravenous, subcutaneous, or intraperitoneal inoculation, it is the bacterial and host factors that determine the development of bacteremia and the potential for a pathogen to invade the central nervous system that primarily are studied. In contrast, experimental models using direct inoculation into the cerebrospinal fluid can reliably produce lethal infections over a predictable time course. Furthermore, because adult animals will not reliably develop meningitis after intranasal or intraperitoneal challenge, infant animals are used. Because these models bypass the natural dissemination of bacteria from the intravascular compartment to the central nervous system, the pathogenesis is artificial. These models, however, are extremely useful for the study of pathogen and host factors leading to meningeal inflammation and resulting complications, and for evaluating potentially useful agents for treatment therapy. During the past decade, the design of clinical studies has been stimulated by findings obtained from these animal models.

Bacterial Meningitis

Initial empiric therapy for community-acquired bacterial meningitis should be based on the possibility that penicillin-resistant pneumococci may be the etiologic organisms and, hence, should include a combination of third-generation cephalosporin (cefotaxime or ceftriaxone) and vancomycin. Ampicillin should be included if the patient has predisposing factors that are associated with a risk for infection with Listeria monocytogenes. Bacterial isolates from the cerebrospinal fluid should be tested for antimicrobial susceptibility. Understanding the significance of inflammatory cytokines in the pathophysiology of bacterial meningitis leads to an understanding of the need to prevent their formation. Dexa- methasone inhibits synthesis of the inflammatory cytokines, interleukin-1 and tumor necrosis factor. Results of clinical trials and meta-analysis suggest that dexamethasone therapy improves the outcome for patients with bacterial meningitis. Dexamethasone should be administered before or with the first dose of antibiotics. The development of therapeutic modalities to downregulate host inflammatory responses, such as those of monoclonal antibodies to cytokines, is of utmost importance.

[Hydration and meningitis]

For almost 20 years, fluid restriction has been applied in the management of bacterial meningitis. This recommendation was based upon the findings of elevated plasma levels of arginine vasopressin in children with bacterial meningitis and their interpretation as evidence for inappropriate secretion of antidiuretic hormone. Recent data indicate that this interpretation was erroneous and that elevated levels of arginine vasopressin is the consequence of hypovolemia in the majority of cases of bacterial meningitis. In addition, fluid restriction appears to worsen the prognosis. As a consequence, not only fluid restriction must not be systematically applied in the management of bacterial meningitis, but appropriate fluid and sodium intakes are necessary to compensate hypovolemia and dehydration. Only a small number of cases with evidence of inappropriate secretion of antidiuretic hormone will require fluid restriction.

Effect of induced hyperglycemia on brain cell membrane function and energy metabolism during the early phase of experimental meningitis in newborn piglets

This study was done to elucidate the mechanism of hypoglycorrhachia and elevated lactate concentrations leading to neuronal dysfunction in neonatal meningitis, and to determine the effects of induced hyperglycemia on these disturbances. Thirty-eight newborn piglets were divided into three groups: 12 in the control group (CG), 12 in the normoglycemic meningitis group (NG), and 14 in the hyperglycemic meningitis group (HG). Meningitis was induced by intracisternal injection of 108 cfu of Escherichia coli. Hyperglycemia (blood glucose 300-400 mg dl-1) was induced and maintained for 60 min before induction of meningitis and throughout the experiment using modified glucose clamp technique. CSF-to-blood glucose ratio decreased significantly in NG. In HG, baseline CSF-to-blood glucose ratio was lower than two other groups, but increased at 1 h after induction of meningitis. CSF lactate concentration was increased progressively in both meningitis groups, and positively correlated with CSF leukocyte numbers (r=0.41, p<0.001) and TNF-alpha level (r=0.43, p<0.001). Brain glucose concentration was significantly increased in HG and showed inverse correlation with CSF leukocyte numbers (r=-0.59, p<0.01). Brain lactate concentration was not significantly different among three groups and positively correlated with the CSF TNF-alpha level (r=0.51, p<0.05). Lipid peroxidation products were increased in NG. Na+,K+-ATPase activity, ATP/PCr concentrations were not different among three groups. Increased intracranial pressure, CSF pleocytosis (214+/-59 vs. 437+/-214/mm3, p<0.02) and increased lipid peroxidation products observed in NG were reduced in HG. These results suggest that hypoglycorrhachia and elevated lactate concentration in the CSF during meningitis originates primarily from the increased anaerobic glycolysis in the subarachnoid space, induced by TNF-alpha and leukocytes. Induced hyperglycemia attenuates the inflammatory responses of meningitis and might be beneficial by providing an increased glucose delivery to meet its increased demand in meningitis.

Reactive oxygen intermediates contribute to necrotic and apoptotic neuronal injury in an infant rat model of bacterial meningitis due to group B streptococci

Reactive oxygen intermediates (ROI) contribute to neuronal injury in cerebral ischemia and trauma. In this study we explored the role of ROI in bacterial meningitis. Meningitis caused by group B streptococci in infant rats led to two distinct forms of neuronal injury, areas of necrosis in the cortex and neuronal loss in the dentate gyrus of the hippocampus, the latter showing evidence for apoptosis. Staining of brain sections with diaminobenzidine after perfusion with manganese buffer and measurement of lipid peroxidation products in brain homogenates both provided evidence that meningitis led to the generation of ROI. Treatment with the radical scavenger alpha-phenyl-tert-butyl nitrone (PBN) (100 mg/kg q8h i.p.) beginning at the time of infection completely abolished ROI detection and the increase in lipidperoxidation. Cerebral cortical perfusion was reduced in animals with meningitis to 37.5+/-21.0% of uninfected controls (P < 0.05), and PBN restored cortical perfusion to 72.0+/-8.1% of controls (P < 0.05 vs meningitis). PBN also completely prevented neuronal injury in the cortex and hippocampus, when started at the time of infection (P < 0.02), and significantly reduced both forms of injury, when started 18 h after infection together with antibiotics (P < 0.004 for cortex and P < 0.001 for hippocampus). These data indicate that the generation of ROI is a major contributor to cerebral ischemia and necrotic and apoptotic neuronal injury in this model of neonatal meningitis.

Near-infrared spectroscopy in experimental pneumococcal meningitis in the rabbit: cerebral hemodynamics and metabolism

Near-infrared spectroscopy is a noninvasive technique which measures oxidized cytochrome aa3, oxygenated Hb, and deoxygenated Hb and calculates total Hb in tissue. This technique, in conjunction with measurement of cerebral blood flow, was used in rabbits with experimental bacterial meningitis to determine whether there was evidence for cerebral energy depletion and alterations in the cerebral vascular bed with infection. Rabbits with meningitis had a significant reduction in cerebral blood flow, cerebral oxidized cytochrome aa3 and a relative increase in the deoxygenated Hb fraction and a decrease in the oxygenated Hb fraction compared with uninfected controls. Total Hb was not significantly different between the two groups. These findings may help clarify the mechanism for some of the intracranial pathophysiologic abnormalities in meningitis.

Evidence for fluid volume depletion in hyponatraemic patients with bacterial meningitis

Since the mechanisms underlying hyponatraemia in meningitis are poorly understood, we retrospectively reviewed the records of 187 paediatric patients with bacterial meningitis treated at the Department of Pediatrics, University of Bern, Switzerland, between 1982 and 1994. The degree of dehydration calculated from naked weight on admission and at 5 days was consistently (by 2.8 x 10(-2) and significantly more pronounced in 30 hyponatraemic (plasma sodium 130 mmol l-1 or less) than in 157 normonatraemic patients (plasma sodium 131 mmol l-1 or more). Furthermore, a tendency towards reduced sodium excretion was noted in hyponatraemic patients. The results suggest that in bacterial meningitis hyponatraemia is mostly induced by clinically latent fluid volume depletion.

Adjunctive dexamethasone therapy for pediatric bacterial meningitis

There have been numerous studies performed to assess the impact of adjunctive corticosteroid therapy on the outcome of pediatric bacterial meningitis. Much of these data are conflicting, which can result in confusion regarding therapeutic efficacy. The present article will review the pathophysiology of this disease, critique the body of medical literature on this aspect of therapy, and provide guidelines for the emergency physician on the use of dexamethasone therapy for bacterial meningitis in children.

Effect of recombinant human tumor necrosis factor-alpha on cerebral oxygen uptake, cerebrospinal fluid lactate, and cerebral blood flow in the rabbit: role of nitric oxide

Among the important pathophysiologic alterations in the brain in bacterial meningitis are abnormalities of cerebral circulation and metabolism; however, the precise mechanisms by which these disturbances occur are not completely delineated. It has been recently recognized that cytokines are produced by tissues in the central nervous system in meningitis and play a critical role in the host inflammatory response. Because these mediators are involved in circulatory and metabolic disturbances in other tissues in sepsis, we investigated the role of tumor necrosis factor-alpha in the central nervous system in a rabbit model. We found that injection of recombinant human TNF into the cisterna magna in the rabbit led to an acute reduction in cerebral oxygen uptake and a more prolonged reduction in cerebral blood flow. This was accompanied by an increase in intracranial pressure and an increase in cerebrospinal fluid lactate. Reduction in oxygen uptake and increases in intracranial pressure and CSF lactate were blocked by pretreatment with L-NAME, an inhibitor of nitric oxide synthase. Reduction in cerebral blood flow was not affected by L-NAME treatment and was due to increased cerebrovascular resistance and reduced oxygen demand. These results suggest that TNF may be a critical mediator of changes in cerebral circulation and metabolism and that some of these changes occur via the nitric oxide pathway.

Bacterial meningitis: mechanisms of disease and therapy

Bacterial meningitis continues to be a serious infectious disease with a high morbidity and mortality in young children. Early recognition and initiation of adequate treatment are the major determinants for a good outcome. Recent advances in our understanding of the host inflammatory response by cytokines may result in the use of new therapeutic strategies. Such modulation of the inflammatory response may reduce the incidence of sequelae and death. The use of steroids as adjunctive therapy in children with bacterial meningitis probably has beneficial effects although the available data are still controversial. Additionally, studies in experimental meningitis models indicate that non-steroidal anti-inflammatory drugs and monoclonal antibodies against bacterial products, cytokines and CD18 on leucocytes reduce the extent of the meningeal inflammation. Human studies to evaluate the efficacy of these immune modulators are expected to start soon. However, prevention of bacterial meningitis by conjugate vaccines against Streptococcus pneumoniae and Neisseria meningitidis will be the most promising development in the next decade.

Blood-brain barrier permeability in staphylococcal cerebritis and early brain abscess

The pattern of radiographic enhancement in cases of brain abscess has been extensively studied, but the magnitude of blood-brain barrier (BBB) damage that accompanies enhancement has not. The question of whether BBB permeability increases continuously as a cerebritis evolves into an abscess was studied. The tracers 3H-labeled aminoisobutyric acid and 14C-labeled butanol were used in a rat Staphylococcus aureus cerebritis model to measure simultaneously BBB permeability and blood flow. The rats were examined at 1, 2, 3, 5, or 7 days after inoculation, and tissue samples were collected from the cerebritis site and uninoculated regions. Permeability of the BBB in the cerebritis region increased to five times the normal values by 72 hours after inoculation, then reached a plateau. The plasma volume in the cerebritis region increased to six times greater than the normal value at 72 hours, then remained unchanged. Uninoculated brain in both ipsilateral and contralateral hemispheres showed no significant changes. Cerebral blood flow was not substantially altered at the inoculated or uninoculated sites. In this model, incidence of BBB damage rises rapidly, reaches a plateau, and does not continue to increase despite the ongoing evolution of a cerebritis into an abscess. The BBB damage is accompanied by an increase in the regional plasma volume, a novel finding that has not been previously reported in central nervous system inflammation. These results suggest that the vascular events contributing to brain edema formation become established early in the cerebritis phase and imply that control of the host's inflammatory response is important in the management of cerebritis-associated brain edema.

Pathogenesis and pathophysiology of bacterial meningitis

Bacterial meningitis remains a disease with associated unacceptable morbidity and mortality rates despite the availability of effective bactericidal antimicrobial therapy. Through the use of experimental animal models of infection, a great deal of information has been gleaned concerning the pathogenic and pathophysiologic mechanisms operable in bacterial meningitis. Most cases of bacterial meningitis begin with host acquisition of a new organism by nasopharyngeal colonization followed by systemic invasion and development of a high-grade bacteremia. Bacterial encapsulation contributes to this bacteremia by inhibiting neutrophil phagocytosis and resisting classic complement-mediated bactericidal activity. Central nervous system invasion then occurs, although the exact site of bacterial traversal into the central nervous system is unknown. By production and/or release of virulence factors into and stimulation of formation of inflammatory cytokines within the central nervous system, meningeal pathogens increase permeability of the blood-brain barrier, thus allowing protein and neutrophils to move into the subarachnoid space. There is then an intense subarachnoid space inflammatory response, which leads to many of the pathophysiologic consequences of bacterial meningitis, including cerebral edema and increased intracranial pressure. Attenuation of this inflammatory response with adjunctive dexamethasone therapy is associated with reduced concentrations of tumor necrosis factor in the cerebrospinal fluid, with diminished cerebrospinal fluid leukocytosis, and perhaps with improvement of morbidity, as demonstrated in recent clinical trials. Further information on the pathogenesis and pathophysiology of bacterial meningitis should lead to the development of more innovative treatment and/or preventive strategies for this disorder.

Brain levels of neuropeptide Y in experimental pneumococcal meningitis

Neuropeptide Y (NPY), which is found in high concentrations in several regions of the brain including nuclei of the brain stem and in nerve fibers surrounding cerebral vessels, has been proposed to play a role in regulating cerebral blood flow (CBF) and systemic vegetative functions. Since CBF is altered during meningitis, we examined whether NPY concentrations changed in various regions of the rabbit brain in response to experimental pneumococcal meningitis. Changes were most pronounced in the medulla, where NPY concentration increased threefold after 48 h of infection. Concomitantly, there was an increase in NPY immunoreactive fibers surrounding small vessels in the dorsolateral medulla, especially in the nucleus tractus solitarius. These results suggest that NPY may play a role in inducing some of the hemodynamic changes seen during pneumococcal meningitis.