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Neurocritical Care

Meningitis

Empiric therapy, LP, and when to image first

Meningitis is a clinical diagnosis. Empiric antibiotics before LP when bacterial is suspected; don't delay for imaging unless there are signs of mass or herniation.

1.When to Suspect

Fever, headache, nuchal rigidity, photophobia. AMS, seizures. Immunocompromise, sinus/ear/neuro surgery. Petechial rash: meningococcus.[+]

2.Imaging Before LP

CT before LP if: focal deficit, papilledema, GCS <10, immunocompromised, seizure, known mass. Otherwise LP first. If imaging delays antibiotics >1 h, give antibiotics before the scan.[+]

3.LP and CSF

Opening pressure. Send: cell count, protein, glucose, Gram stain, culture. Add HSV PCR, cryptococcal Ag, VDRL, AFB/fungal as indicated.[+]

Bacterial: high WBC (PMN-predominant), low glucose, high protein. Viral: lymphocytic, glucose often normal. TB/fungal: lymphocytic, low glucose.[+]

4.Empiric Therapy

Empiric: Vancomycin + ceftriaxone (or cefotaxime). Add ampicillin if >50 y, immunocompromised, or Listeria risk. Dexamethasone with first dose for suspected pneumococcal (adults).[+]

HSV: Acyclovir 10 mg/kg IV q8h until HSV PCR negative and another cause found.[+]

Give empiric antibiotics as soon as bacterial meningitis is suspected. Do not wait for LP or imaging if that would delay by more than ~1 hour.

Tap underlined terms for details · Tap [+] to expand

Frequently asked questions

What is the empiric antibiotic regimen for bacterial meningitis?

Empiric therapy for community-acquired bacterial meningitis is vancomycin (15–20 mg/kg IV q8–12h, target trough 15–20 µg/mL) plus a third-generation cephalosporin — ceftriaxone 2 g IV q12h (or cefotaxime 2 g IV q4–6h). Add ampicillin 2 g IV q4h to cover Listeria monocytogenes for patients >50 years, immunocompromised, pregnant, or with alcohol use disorder. Substitute meropenem 2 g IV q8h for the cephalosporin if Pseudomonas is suspected (post-neurosurgical, penetrating head trauma, CSF shunt). Antibiotics should be given within 60 minutes of presentation; do not delay for LP or imaging if access is delayed.

When should dexamethasone be given in bacterial meningitis?

Dexamethasone 0.15 mg/kg IV every 6 hours for 4 days, started 10–20 minutes before — or concurrently with — the first dose of antibiotics. Adjunctive dexamethasone reduces mortality and unfavorable outcomes in pneumococcal meningitis (de Gans & van de Beek, NEJM 2002; IDSA 2004 guidelines). Continue only if CSF Gram stain or culture confirms Streptococcus pneumoniae or Haemophilus influenzae. If a different pathogen is identified or cultures are negative, dexamethasone is generally discontinued. Do not start dexamethasone after antibiotics have already been given — the meningeal inflammatory effect that the steroid blunts has already occurred.

When is LP contraindicated before antibiotics, and what should I do instead?

Obtain CT head before LP if any of the following are present: immunocompromised state, history of CNS disease, new-onset seizure within 1 week, papilledema, abnormal level of consciousness (GCS <10), or focal neurologic deficit (IDSA 2004). In these patients, the sequence is: draw blood cultures → give empiric antibiotics and dexamethasone immediately → then obtain CT → then LP if no mass effect. Antibiotics must not be delayed waiting for imaging. CSF Gram stain remains positive for several hours after antibiotic administration, and culture yield drops only modestly within the first 2–4 hours.

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