From the Guidelines
Before performing a lumbar puncture, a thorough clinical assessment, rather than a CT scan, should be used to determine if it is safe to proceed, looking for signs suggestive of a shift of brain compartments, such as focal neurological signs and a reduced Glasgow Coma Scale (GCS) score, particularly if the GCS is ≤12 1. To check for increased intracranial pressure (ICP) prior to a lumbar puncture, the following steps should be taken:
- Perform a thorough neurological examination to identify warning signs such as altered mental status, focal neurological deficits, or Cushing's triad (hypertension, bradycardia, and irregular breathing) 2.
- Assess the patient's GCS score, as a score of ≤12 may indicate a need for a brain scan before proceeding with the lumbar puncture 1.
- Look for clinical signs suggestive of brain shift, such as papilledema on fundoscopic examination, although this may not always be present or easily visible 1.
- Consider the patient's overall clinical condition, including any history of immunocompromise or coagulopathy, which may increase the risk of complications from the lumbar puncture 3. If any of these signs or conditions are present, a CT scan of the head should be performed to identify any space-occupying lesions, cerebral edema, or other causes of increased ICP before proceeding with the lumbar puncture 1, 2. However, it is essential to note that a CT scan does not detect raised intracranial pressure, and the decision to perform a lumbar puncture should be based on a thorough clinical assessment, rather than relying solely on imaging results 1. In patients with suspected meningitis who require immediate treatment, empiric antibiotics should be administered before neuroimaging to avoid treatment delays, as delays in antibiotic treatment can lead to increased mortality 1.
From the Research
Checking for Increased ICP Prior to a Lumbar Puncture
To check for increased intracranial pressure (ICP) prior to a lumbar puncture, several methods can be considered:
- Computed Tomography (CT) scans: CT scans can be used to identify signs of elevated ICP, such as sulcal obliteration, lateral ventricle compression, third ventricle compression, midline shift, and herniation 4.
- Clinical criteria: Certain clinical criteria, such as impaired mental status, can be used to determine the need for a CT scan prior to a lumbar puncture 5, 6.
- Physical examination: Physical examination signs, such as pupillary dilation, posturing, and Glasgow coma scale, can be used to assess for increased ICP, but their sensitivity and specificity are limited 7.
- Sonography of the optic nerve sheath diameter (ONSD): ONSD sonography has shown promise in detecting elevated ICP, with a pooled area under the ROC curve of 0.94 7.
- Transcranial Doppler pulsatility index (TCD-PI): TCD-PI has poor performance in detecting raised ICP, with an area under the ROC curve ranging from 0.55 to 0.72 7.
Indications for CT Scan Prior to Lumbar Puncture
The decision to perform a CT scan prior to a lumbar puncture should be based on the individual patient's risk factors and clinical presentation:
- Patients with suspected bacterial meningitis should undergo a lumbar puncture promptly, and a CT scan should only be performed if there are signs of increased ICP or other contraindications to lumbar puncture 6.
- Patients with impaired mental status, focal neurologic deficits, or other signs of increased ICP should undergo a CT scan prior to a lumbar puncture 5, 6.
- The presence of certain clinical criteria, such as brain shift or raised CSF pressure, can indicate the need for a CT scan prior to a lumbar puncture 8.