Quick Recap
Neurology System, Protocol 5/12.
1. Definition & Epidemiology
Most common type of CNS infection; mortality reaches 60% in bacterial meningitis — delays in diagnosis and timely antimicrobial treatment can be catastrophic. Complications include abscess formation, hydrocephalus, cerebral infarcts, and seizures; neurosurgical procedures, indwelling hardware, and penetrating skull injuries complicate management further.
2. Presentation
Classic tetrad: fever, nuchal rigidity, headache, altered mental status — most patients have at least 2 of these; the absence of ALL of them has a very high negative predictive value for bacterial meningitis. Bacterial meningitis has an acute onset and rapid deterioration, contrasting with the more subtle course of aseptic meningitis (usually viral — enteroviruses, arboviruses, HSV-2 — or noninfectious). Petechial rash suggests meningococcal etiology; extra-meningeal infection foci (otitis, sinusitis, endocarditis, pneumonia) suggest streptococcal etiology. Higher index of suspicion needed in immunocompromised patients, in whom any single symptom may be the sole manifestation.
3. Immediate Stabilization / General Approach — "If You Consider an LP, You Should Do It"
Delays in antibiotic therapy are directly associated with increased mortality — every patient with suspected CNS infection gets prompt empiric antimicrobials, and LP should never delay this.
Sequence:
- Two sets of blood cultures BEFORE antibiotics (50-90% of bacterial meningitis patients have positive blood cultures, higher yield pre-antibiotic)
- Determine if CT head is needed BEFORE LP (Section 4) — but this determination and imaging itself should NOT delay antibiotic administration if there will be any meaningful wait
- LP as soon as safely possible — antimicrobials may reduce CSF culture yield if given first, but Gram stain can still be positive even after antibiotics have started, so starting antibiotics first does not blind you diagnostically
- Empiric antibiotics + dexamethasone (Section 6) started promptly, broad-spectrum until organism isolated
Checklist:
4. Lumbar Puncture — When to CT First, and Contraindications
CT head BEFORE LP indicated for: immunocompromised state, known CNS lesion history, recent seizure (within ~1 week), altered level of consciousness, new focal neurologic deficit, papilledema, suspicion of raised ICP. CT does NOT completely rule out herniation risk even when normal — clinical judgment still matters.
Absolute LP contraindications: space-occupying posterior fossa lesion, midline shift, effacement of basal cisterns/4th ventricle, skin infection at puncture site, lumbar epidural abscess/empyema, signs of impending herniation (pupillary changes, decerebrate posturing, altered respiration, brainstem signs).
Relative/correctable contraindications: INR >1.6 (some sources cite >1.4-1.5), platelet count <50,000/mcL (some sources cite <100,000) — correct coagulopathy with FFP/platelets before LP to prevent spinal epidural hematoma, rather than treating this as an absolute barrier.
If LP is deferred/delayed: do NOT delay antibiotics — rely on blood cultures (yield >50%) and proceed with prompt empiric treatment; obtain the LP once safely feasible.
5. CSF Analysis
Always record opening pressure. Send: cell count with differential, glucose, protein, Gram stain, bacterial culture; additional tests as indicated by clinical picture (cryptococcal antigen, HSV PCR, WNV IgM, multiplex NAAT panel covering ~14 CNS pathogens including bacteria/viruses/Cryptococcus). Save extra CSF for additional testing once initial results suggest a likely organism class.
CSF pattern by etiology:
Parameter | Normal | Bacterial | Viral | Fungal |
Opening pressure (cm H2O) | 10-20 | >18 (increased) | 9-18 (normal-mild increase) | >18 |
WBC/mcL | 0-5 | 100-10,000 (>=1000 typical) | 5-1,000 (10-1000) | 5-1,000 |
% Neutrophils | — | >80 | <20 (lymphocyte predominant) | <20 |
Protein (mg/dL) | 15-40 | 100-500 (increased) | <100 (mildly increased) | >100 |
CSF:serum glucose ratio | >0.6 | <=0.4 (glucose <40 absolute) | Normal (>40) | <40 |
Gram stain positive | — | 60-90% | 0% | 0% |
Culture positive | — | 70-85% | 50% | 25-50% |
6. Empiric Treatment
Etiology | Regimen | Notes |
Acute bacterial meningitis | Vancomycin 15-20mg/kg IV q8h PLUS ceftriaxone 2g IV q12h | Add ampicillin 2g IV q4h if age >=50 or immunosuppressed (Listeria coverage); add acyclovir 10mg/kg q8h if HSV meningoencephalitis concern; add dexamethasone 0.15mg/kg q6h x4 days, started AT/BEFORE the first antibiotic dose |
Healthcare-associated ventriculitis/meningitis | Vancomycin PLUS cefepime 2g IV q8h, OR vancomycin PLUS meropenem 2g IV q8h | Linezolid 600mg q12h as vancomycin alternative; meropenem provides empiric Listeria coverage |
Viral meningitis | Supportive care only | — |
HSV encephalitis | Acyclovir 10mg/kg IV q8h | — |
Severe beta-lactam allergy | Vancomycin PLUS moxifloxacin 400mg IV q24h | Add aztreonam 2g IV q6h or ciprofloxacin 400mg IV q8h if antipseudomonal coverage needed; add TMP-SMX 5mg/kg/day (trimethoprim component) if Listeria coverage needed |
Cefepime as ceftriaxone alternative when gram-negative/Pseudomonas coverage needed (immunocompromised/neutropenic, impaired mucosal barriers, nosocomial meningitis risk).
Acyclovir should be added for ANY patient >50 years old with encephalitis symptoms, given HSV's status as the most treatable major encephalitis cause — err toward covering it empirically in this age group.
7. Dexamethasone — The Nuanced Evidence
Use remains genuinely controversial at the meta-analysis level: a Cochrane meta-analysis found NO overall mortality benefit. However, subgroup analysis showed decreased mortality specifically in S. pneumoniae meningitis, and decreased hearing loss/short-term neurologic sequelae in H. influenzae meningitis. Current IDSA guidance: give dexamethasone to ALL patients with suspected or proven pneumococcal meningitis, timed at or before the first antibiotic dose (this timing is critical — giving it after doesn't replicate the benefit). Stop dexamethasone if an alternative (non-pneumococcal) etiology is subsequently identified.
8. Investigations Beyond CSF
CT/MRI per Section 4 criteria; HIV 4th-generation test in any patient with altered mental status (dramatically changes differential/workup if positive); autoimmune/paraneoplastic workup if atypical/refractory course; consider EEG if seizures/altered mental status disproportionate to apparent severity (nonconvulsive seizure as a differential for persistent altered mental status, cross-reference Status Epilepticus protocol).
9. Treatment Duration
Duration is organism-specific (e.g., N. meningitidis typically shorter courses of ~7 days; S. pneumoniae ~10-14 days; gram-negative bacilli/Listeria longer, 21 days or more) — confirm against current local/IDSA duration tables once organism identified rather than applying a single fixed course to all bacterial meningitis.
10. Organ Support
Standard ICU supportive care; ICP management if elevated (see Raised ICP protocol) — mass lesion/hydrocephalus complications may require neurosurgical CSF diversion; seizure management per Status Epilepticus protocol if seizures occur (not prophylactic).
11. Consultation Matrix
Consultation | Trigger | Timing |
Infectious Disease | All suspected/confirmed CNS infection | Immediate |
Neurosurgery | Hydrocephalus, abscess, need for ICP monitoring/CSF diversion | As complications arise |
Neurology | Seizures, encephalitis overlap, diagnostic uncertainty | As needed |
12. Monitoring Framework
Serial neuro checks, temperature trend, repeat imaging if new deficit/failure to improve (concern for abscess, hydrocephalus, infarct), CSF re-analysis if not improving on appropriate therapy, hearing assessment before discharge (H. influenzae/pneumococcal meningitis-associated hearing loss risk).
13. Complications
Hydrocephalus, cerebral abscess, cerebral infarcts (vasculitis-mediated), seizures, hearing loss (esp. H. influenzae/pneumococcal), SIADH, death. Prevention: prompt antibiotics + dexamethasone timing, appropriate organism-targeted duration. Rescue: neurosurgical intervention for hydrocephalus/abscess, seizure management if occurring.
14. Escalation & De-escalation
Escalate: failure to improve on appropriate empiric therapy, new focal deficit -> repeat imaging (abscess/infarct/hydrocephalus), reconsider organism coverage.
De-escalate: organism identified and susceptibilities known -> narrow antibiotics (e.g., discontinue vancomycin once penicillin-susceptible pneumococcus confirmed), complete organism-specific duration, discontinue dexamethasone if non-pneumococcal cause confirmed.
15. ICU Discharge Criteria
Clinically improving/afebrile trend, no new neurologic deficits, antibiotics narrowed and on definitive course, complications (hydrocephalus, abscess) addressed or stable, hearing assessment arranged if indicated.
16. Documentation & Medicolegal Checklist
17. Key Guidelines
IDSA Practice Guidelines for the Management of Bacterial Meningitis (Tunkel et al.) — primary reference for dexamethasone and antibiotic selection guidance.
18. Controversies
Dexamethasone's overall mortality benefit is NOT established at the aggregate level (Cochrane meta-analysis negative) despite guideline-level recommendation for pneumococcal meningitis specifically — this is a case where subgroup evidence drives practice ahead of the overall trial result, worth being transparent about rather than presenting dexamethasone use as unambiguously evidence-based across all bacterial meningitis. Precise coagulopathy cutoffs for safe LP (INR/platelet thresholds) vary across sources without a single validated number.
19. References
- Approach to CNS Infections chapter. Washington Manual of Critical Care, 4th ed, 2025 (Ch. 37, and Ch. 64 duplicate/expanded content).
- Tunkel AR, Hartman BJ, Kaplan SL, et al. Practice guidelines for the management of bacterial meningitis. Clin Infect Dis. 2004;39(9):1267-1284 (IDSA; verify current edition).
- Chawla R, Gauba C, Kansal S, Tiwari A. Lumbar Puncture. ICU Protocols: A Step-wise Approach, 2nd ed. Springer; 2020 (Ch. 49).
- Brouwer MC, McIntyre P, Prasad K, van de Beek D. Corticosteroids for acute bacterial meningitis. Cochrane Database Syst Rev. 2015;9:CD004405.
See also: Encephalitis (Neurology System) for the closely overlapping presentation and workup.