EM Command Center / Neurology & Psychiatry • 3 min read • 4 sections

Central Nervous System Infections

Comprehensive emergency protocol for life-threatening CNS infections. Features empiric antibiotic timing and age-based regimens, the FAILS criteria for CT before lumbar puncture, dexamethasone administration before antibiotics for S. pneumoniae, CSF analysis interpretation tables, and spinal epidural abscess management.

Resuscitation Quick Ribbon (First 2 Minutes)

High-Acuity

Resus:Start empiric IV antibiotics and dexamethasone IMMEDIATELY; never delay antimicrobial therapy for a head CT or lumbar puncture.

Dexamethasone:10 mg IV (0.15 mg/kg in children) given immediately before or with the first antibiotic dose.

Empiric adult regimen (1-50 yrs):Ceftriaxone 2 g IV q12h + Vancomycin 15-20 mg/kg IV q8-12h.

Age > 50 yrs or immunocompromised:Add Ampicillin 2 g IV q4h to cover Listeria monocytogenes.

Suspected viral encephalitis (altered mental status, seizures, temporal lobe signs):Add Acyclovir 10 mg/kg IV q8h.

Bottom-Line Clinical Pearl

Administer Dexamethasone 10 mg IV BEFORE or CONCURRENTLY with the first dose of empiric antibiotics in suspected bacterial meningitis. Dexamethasone significantly reduces mortality and sensorineural hearing loss without increasing adverse outcomes.

1. Empiric Antimicrobial Regimens by Age & Risk Profile

Patient Population	Most Common Pathogens	Empiric Antibiotic / Antiviral Regimen
Neonates (< 1 month)	Group B Streptococcus (GBS), E. coli, Listeria monocytogenes	Ampicillin 50 mg/kg IV q8h + Cefotaxime 50 mg/kg IV q8h (or Gentamicin). Avoid Ceftriaxone in neonates due to biliary sludging and hyperbilirubinemia.
Infants & Adults (1 month to 50 years)	Streptococcus pneumoniae, Neisseria meningitidis	Ceftriaxone 2 g IV q12h + Vancomycin 15-20 mg/kg IV q8-12h (target trough 15-20 mcg/mL) + Dexamethasone 10 mg IV.
Adults > 50 years, Alcoholism, or Immunocompromise	S. pneumoniae, N. meningitidis, Listeria monocytogenes, Gram-negative bacilli	Ceftriaxone 2 g IV q12h + Vancomycin 15-20 mg/kg IV + Ampicillin 2 g IV q4h (covers Listeria) + Dexamethasone 10 mg IV.
Post-Neurosurgery / Penetrating Trauma / CSF Shunt	Staphylococcus aureus (including MRSA), Pseudomonas aeruginosa, coagulase-negative Staph	Vancomycin 15-20 mg/kg IV + Cefepime 2 g IV q8h (or Meropenem 2 g IV q8h).
Suspected Viral Encephalitis	Herpes Simplex Virus (HSV-1), Varicella Zoster Virus (VZV)	Add Acyclovir 10 mg/kg IV q8h (infused over 1 hr to prevent crystalline nephropathy).

2. Indications for Head CT Before Lumbar Puncture (The FAILS Mnemonic)

Performing an LP in the presence of mass effect or obstructive hydrocephalus can cause fatal uncal or tonsillar herniation. Perform non-contrast Head CT prior to LP if ANY FAILS criterion is met:

F - Focal Neurological Deficit (e.g., hemiparesis, facial droop, visual field cut)
A - Altered Mental Status (GCS < 15, severe lethargy or coma)
I - Immunocompromised State (HIV/AIDS, organ transplant, immunosuppressive therapy)
L - Lesion (Papilledema on funduscopy or signs of increased ICP)
S - Seizure within the past 7 days

Critical Pitfall / Contraindication

Critical Rule: If a head CT is required prior to LP, DRAW BLOOD CULTURES AND ADMINISTER EMPIRIC ANTIBIOTICS + DEXAMETHASONE IMMEDIATELY before transporting the patient to the scanner. Never delay antibiotics for neuroimaging.

3. CSF Profile Interpretation Table

Parameter	Normal CSF	Bacterial Meningitis	Viral / Aseptic Meningitis	Fungal / TB Meningitis
Opening Pressure	10 - 20 cmH2O	Elevated (> 25 - 50 cmH2O)	Normal to mildly elevated	Markedly elevated (> 25 - 40 cmH2O)
WBC Count	< 5 cells/mcL	1,000 - 20,000+ cells/mcL	50 - 500 cells/mcL	100 - 500 cells/mcL
Predominant Cell	Mononuclear / Lymphs	Neutrophils / Polys (> 80%)	Lymphocytes (> 80%)	Lymphocytes
Glucose Level	> 60% of serum (45-80 mg/dL)	Markedly decreased (< 40 mg/dL or CSF/serum ratio < 0.4)	Normal (> 60% of serum)	Markedly decreased (< 30 mg/dL or ratio < 0.3)
Protein Level	15 - 45 mg/dL	Markedly elevated (> 100 - 500 mg/dL)	Normal to mildly elevated (< 100 mg/dL)	Markedly elevated (> 100 - 500 mg/dL)
Gram Stain & PCR	Negative	Positive in 60-80% untreated	Enterovirus / HSV PCR positive	India ink / Cryptococcal antigen positive; AFB positive

4. Spinal Epidural Abscess (SEA)

Spinal epidural abscess is one of emergency medicine's most frequently missed diagnostic traps, resulting in permanent paraplegia:

Classic Diagnostic Triad: (1) Severe focal spine pain; (2) Fever; (3) Neurologic deficits (radiculopathy, weakness, bowel/bladder dysfunction). NOTE: Triad is present in only 10-15% of patients at initial ED presentation!
High-Risk Profiles: IV drug use, spinal instrumentation/epidural catheter, diabetes mellitus, end-stage renal disease on hemodialysis, systemic bacteremia.
Screening Biomarkers: ESR and CRP are elevated in > 95% of cases. An ESR > 20 mm/hr and CRP > 10 mg/L in a patient with back pain and risk factors strongly warrants advanced imaging.
Diagnostic Gold Standard: Emergency contrast-enhanced MRI of the ENTIRE spine (skip lesions occur in 10-20% of cases).
Management: Immediate Vancomycin (15-20 mg/kg IV) + Cefepime (2 g IV) + Emergent Spine Surgery Consultation for decompression.

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