How can I effectively assess the risks and benefits of lumbar puncture in a patient with suspected meningitis?

To effectively assess the risks and benefits of performing a lumbar puncture (LP) in a patient with suspected meningitis, first evaluate for any contraindications that increase the risk of complications. Do not perform LP if the patient has extensive or rapidly spreading purpura, infection at the lumbar puncture site, or risk factors for an evolving space-occupying lesion. Additionally, avoid LP if there are signs of raised intracranial pressure such as new focal neurological features (including seizures or posturing), abnormal pupillary reactions, a Glasgow Coma Scale (GCS) score of 9 or less, or a progressive and sustained or rapid fall in level of consciousness. In these cases, neuroimaging should be performed before LP to assess for space-occupying lesions or raised intracranial pressure, and LP should be deferred until these factors are resolved ¹.

Before performing LP, stabilise the patient by managing unprotected airway, respiratory compromise, shock, uncontrolled seizures, and bleeding risk to reduce procedural risks ¹.

Consider the timing of LP relative to antibiotic administration: perform LP before starting antibiotics unless it is unsafe or would cause a clinically significant delay in antibiotic treatment. If antibiotics have already been started, perform LP as soon as it is safe to do so ¹.

Measure blood glucose immediately before LP to calculate the cerebrospinal fluid (CSF) to blood glucose ratio, which aids interpretation of CSF results ¹,².

Weigh the diagnostic benefits of obtaining CSF for cell counts, protein, glucose, microscopy, culture, and PCR against the risks of LP in the clinical context. The benefits include confirming bacterial meningitis and guiding targeted treatment, while risks include potential brain herniation if raised intracranial pressure is present ¹.