Management

Once the possibility of bacterial meningitis is considered, treatment should be given without delay. Next to the conscious level on admission, the factor that has the most deleterious effect on prognosis is delay in beginning treatment.87 We recommend that all adult patients in whom a diagnosis of bacterial meningitis is suspected should be given parenteral penicillin or ceftriaxone while urgent transfer to hospital is arranged. If the patient arrives at hospital without having received any prehospital antibiotics then they should be given before any further investigations, other than blood cultures. Pre-admission antibiotics are unlikely to obscure the diagnosis of bacterial meningitis.88

Blood cultures and CSF examination are the best ways to confirm the diagnosis of bacterial meningitis and, in established meningitis, there is usually no difficulty in determining the aetiology. In all cases blood cultures and a coagulation screen should be set up immediately, whether or not pre-admission antibiotics have been given.88 In meningococcal disease organisms may be identified in skin aspirates from areas of rash89 and meningococci can also be identified from swabs taken perorally from the posterior pharyngeal wall.90

The diagnosis of bacterial meningitis is ultimately based on examination of CSF.80 However, bacterial meningitis raises the intracranial pressure. In most cases physiological mechanisms cope and no long term untoward effects result. Sometimes, however, intracranial pressure may rise to potentially lethal levels, with cerebral oedema and brain herniation: in such circumstances, a lumbar puncture can lead to rapid deterioration and death. To reconcile this with the necessity of reaching an early diagnosis is, in some cases, difficult, the correct decision depending on experience and a degree of luck. It should not be left to junior members of the medical team. Brain imaging, usually with CT, should be undertaken immediately if there are focal neurological signs, papilloedema, the conscious level is reduced, or if there are frequent seizures. One report91 suggested that CT had little influence on the management of bacterial meningitis in children but it did not address the problem of recognition of raised ICP. Imaging does allow other pathologies that may present like bacterial meningitis to be excluded -subarachnoid haemorrhage, infarction, tumour, and brain abscess. Unfortunately, a normal CT scan does not always mean that it is safe to proceed to lumbar puncture, and cerebral herniation and death do occur as the result of lumbar puncture in cases of suspected meningitis.92

Contraindications to lumbar puncture include presence of signs of raised ICP - unless there is a normal CT or MRI scan - severe shock or a coagulation disorder. If, therefore, there is a confident clinical diagnosis of meningococcaemia with a typical rash, then lumbar puncture should not be undertaken.88,93 CSF may be examined later when it is considered to be safe and evidence of bacterial infection can be found by demonstration of bacterial DNA by PCR.88 94 95 Anxiety that infection may be introduced to CSF by lumbar puncture in patients with bacteraemia is largely unfounded.

CSF findings in bacterial meningitis are of a raised cell count (usually in the range 100-5000) with polymorphs predominating. The protein content is increased and the glucose is reduced. A sample of blood should be taken at the time of lumbar puncture for comparison; a ratio of CSF : blood glucose of less than 03 is abnormal and is found in about three quarters of patients.96 Any one of the following parameters is 99% or more predictive of bacterial rather than viral meningitis: a CSF : blood glucose ratio below 0 23; a protein above 220 mg/dl; more than 1180 x 106/L neutrophils or more than 2000 x 106/L total white cells.97 Identification of the organism under the microscope or on culture should be possible in up to 90% of patients (less than 50% if antibiotics have already been given for more than 24 hours).96,98 If the CSF findings suggest bacterial meningitis but the gram stain is negative then latex agglutination tests are available for all the common meningeal pathogens.80 However, although these tests can provide rapid results a negative result does not rule out bacterial meningitis and they are not widely used in the United Kingdom. A PCR based test for the detection of N. meningitidis from both peripheral blood and CSF has been in routine use since 1996 in the United Kingdom.94,99 This test is sensitive and specific and can also provide information on serogroup to aid serological investigations.100 PCR tests are also available for the detection of S. pneumoniae and H. influenzae. The S. pneumoniae PCR can also provide information on penicillin sensitivity of the organism.

As stated earlier, once the diagnosis of bacterial meningitis is suspected, antibiotic treatment should be started on a "best guess" basis (Box 9.3) and a CSF examination performed as soon as possible. Precedence is given to maintaining cardiorespiratory function, adequate oxygenation, and tissue perfusion while the causal organism is being identified and a specific antibiotic regimen determined. If no organism is found on gram stain, the "best guess" antibiotic treatment is continued (Box 9.3).

To treat meningitis effectively, it is necessary to achieve adequate bactericidal levels of antibiotic in CSF at least 10-fold higher than the minimal bactericidal concentration (MIC) in vitro for the particular organism.88 Ideally, the antibiotic should be lipid soluble to facilitate transfer across the blood-brain barrier but this is not usually a problem in

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Free Yourself from Panic Attacks

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