Make the Diagnosis: Lumbar Puncture to Diagnose Bacterial Meningitis
Why Do a Lumbar Puncture?
A lumbar puncture (LP) to obtain cerebrospinal fluid (CSF) is necessary for diagnosing bacterial meningitis because neither individual symptoms or signs or combinations of findings have sufficient diagnostic accuracy. In addition, microbiological culture of CSF is necessary to guide antibiotic therapy. The basic approach to LP is the same whether or not bacterial meningitis is the most likely diagnosis.
Headache can occur in up to 60% of patients who undergo LP, and backache can occur in up to 40% of patients.1 More serious adverse events are rare and include cerebral herniation, intracranial subdural hemorrhage, spinal epidural hemorrhage, and infection.
In the absence of focal neurological findings, altered mental status, or papilledema, studies suggest that an LP can be performed without prior neuroimaging.2, 3 Patients at increased risk of having a lesion on neuroimaging that would contraindicate an LP include those with focal neurological findings (likelihood ratio (LR), 4.3; 95% confidence interval (CI), 1.9-10), papilledema (LR, 11; 95% CI, 4.8-43), or clinical judgment that there is a computed tomographic (CT) contraindication. Local infection of the skin or soft tissues overlying the needle insertion site is a contraindication to LP. Coagulation defects (including those from the use of anticoagulant drugs) may increase the relative risk of epidural hemorrhage and paraparesis, but this cannot be determined with certainty since the CI for the relative risk is broad and crosses 1.0. It is not known if there is a threshold platelet count value that contraindicates use of LP.
Review the rationale and adverse events with the patient so that informed consent is obtained.
When neuroimaging is believed to be necessary and meningitis is suspected, antibiotics should be immediately started without waiting for the imaging results.
Plan for the procedure to make sure you know which laboratory tests you will be ordering.
Examine the contents of a LP kit so that you are familiar with the needle type, pressure-monitoring column, and collection vials.
Obtain a serum glucose value for comparison to the CSF result.
No studies evaluate the success of the most commonly used patient position, lateral recumbent with knees to chest, compared to alternatives of having the patient sit and bend forward over an adjustable bedside stand or having the patient sit with feet supported and chest resting on the knees. However, the interspinous distance is greatest when the patient is sitting with the feet supported. Unfortunately, the CSF pressure cannot be measured in that position.
Lumbar puncture is usually performed with the patient in the lateral recumbent position ...