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INTRODUCTION

Lumbar puncture (LP) is performed to sample the cerebrospinal fluid (CSF) surrounding the brain and spinal cord. The majority of the CSF is in the subarachnoid space, where the arachnoid membranes bridge the sulci of the brain, in the basal cisterns and around the spinal cord. Cerebrospinal fluid moves within the ventricles and subarachnoid spaces under the influence of hydrostatic pressure generated by the production of CSF by the choroid plexus of the lateral third and fourth ventricles. The volume of CSF in humans is 140 to 150 mL of which only 30 to 40 mL is actually in the ventricular system, with a production rate of 21 mL/h. The turnover rate of total CSF is about 5 hours for an average sized human. Cerebrospinal fluid cushions the brain, regulates brain extracellular fluid, allows for distribution of neuroactive substances, and collects the waste products produced by the brain.

Computed tomography (CT) scan performance before an LP in cases of suspected meningitis is not warranted or recommended unless the patient has grossly altered mental status, active and recent seizures, focal neurologic signs, or papilledema. Patients with these findings or clinical risk factors should have a CT scan to identify mass lesions and other causes of increased intracranial pressure (ICP).

The authors routinely use bedside ultrasound to map the anatomic landmarks prior to virtually all LP attempts. Fluoroscopy-guided LP may be considered for the extremely challenging patient in which bedside LP has failed or in patients with spinal hardware. Fluoroscopy-guided LP shows the bony structures of the lumbar spine and provides real-time information about the position of the needle as it is being inserted. Fluoroscopy-guided LP is usually performed by an interventional radiologist in the radiology suite. Use of fluoroscopy requires the patient to lie in the prone position which makes the measurement of opening pressures more challenging.

Table 125-1Basic Considerations

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