Bacterial Meningitis

Definition

Epidemiology

• H. influenzae was once the leading cause; incidence dropped sharply after the Hib vaccine (early 1990s).
• Worldwide, bacterial meningitis remains a major cause of mortality and morbidity, particularly in low-income countries. — Goldman-Cecil Medicine; Rosen's Emergency Medicine

Etiology by Age

• Post-neurosurgery/trauma: Coagulase-negative staphylococci, S. aureus, Cutibacterium acnes, Pseudomonas
• Meningococcal disease: Most common in young adults in close quarters (dormitories, military barracks); Groups A, B, C predominate

Pathogenesis

1. Nasopharyngeal colonization → mucosal invasion
2. Bacterial capsules resist host defenses → bacteremia
3. Bacteria cross the blood-brain barrier into CSF, where host defenses are weak
4. Bacterial proliferation → cytokine release (TNF, IL-1, IL-6) → meningeal/subarachnoid inflammation
5. Increased blood-brain barrier permeability → cerebral edema
6. Cerebral vasculitis + raised intracranial pressure (ICP)
7. Reduced cerebral blood flow → cerebral hypoxia

Clinical Features

Classic Triad (present in ~85% of adults)

1. Fever
2. Severe headache
3. Neck stiffness (nuchal rigidity)

Other Features

• Nausea/vomiting (35%)
• Seizures (30% adults; 40% neonates)
• Cranial nerve palsies, focal neurologic deficits (10–20%)
• Photophobia, phonophobia
• Altered consciousness, lethargy, obtundation

Meningeal Signs

• Kernig's sign: Resistance to knee extension with hip and knee flexed at 90°
• Brudzinski's sign: Involuntary knee flexion when neck is rapidly flexed

Special Populations

Papilledema early in the course is rare (<1%) and should prompt consideration of brain abscess or mass lesion.

Diagnosis

CT Before LP? (IDSA criteria)

Critical: Do NOT delay antibiotics while waiting for CT. Draw blood cultures and start empiric antibiotics immediately, then proceed with LP/CT.

CSF Analysis

Gram Stain & Culture

• Gram stain: positive in 60–90% of community-acquired cases; specificity >97%
• Blood cultures: always obtained before antibiotics
• PCR: helpful for culture-negative cases

Management

Empiric Antibiotic Therapy (Adults, Community-Acquired)

• Avoid ceftriaxone in hyperbilirubinemic neonates → use cefotaxime instead (displaces bilirubin from albumin)
• Hospital-acquired/post-surgical: use cefepime (2 g q8h) for broader gram-negative coverage
• Cephalosporin allergy: meropenem or chloramphenicol
• Listeria confirmed: add gentamicin to ampicillin (with caution in renal dysfunction)

Adjunctive Dexamethasone

• 0.15 mg/kg (up to 10 mg) IV q6h × 4 days
• Give 20–30 minutes before (or with) the first antibiotic dose
• Benefit:
  • ↓ Mortality in pneumococcal meningitis
  • ↓ Hearing loss in H. influenzae meningitis
• Discontinue if Listeria is identified — dexamethasone increases adverse outcomes in Listeria CNS infection
• Benefit demonstrated in high-income countries; not clearly shown in low-income settings

Complications

• Cerebral edema and herniation
• Hydrocephalus
• Hearing loss (especially post-H. influenzae)
• Stroke / cerebral vasculitis
• Subdural empyema
• Residual neurologic deficits (most common with pneumococcal meningitis)
• Waterhouse-Friderichsen syndrome (bilateral adrenal hemorrhage) — classically with meningococcal disease

Prognosis

• Overall mortality: ~15%
• Listeria meningitis: up to 27% mortality (highest)
• Pneumococcal meningitis: highest rate of residual neurologic deficits
• Many survivors have lasting neurologic sequelae

Prevention (Vaccination)

Key Teaching Points

1. Triad (fever + headache + neck stiffness) present in 85% — absence does not rule out meningitis
2. Never delay antibiotics for CT or LP — give empiric treatment immediately if clinical suspicion is high
3. Dexamethasone before antibiotics for pneumococcal and H. influenzae meningitis
4. Add ampicillin in neonates and adults >50 years for Listeria coverage
5. Petechial/purpuric rash = meningococcal disease until proven otherwise — treat as emergency
6. CSF: PMN pleocytosis + low glucose + high protein = bacterial pattern

Bacterial Meningitis: ICU Management on Mechanical Ventilation

Why Intubation Is Required

In a multicenter ICU cohort of 255 pneumococcal meningitis patients (2023), invasive mechanical ventilation was independently associated with early treatment failure (OR 10.74, p<0.001), confirming it is a marker of severe disease. 30-day mortality was 13.7%. — Martín-Cerezuela et al., Critical Care 2023 [PMID 36823625]

Immediate Priorities ("Don't Miss" Steps)

1. Antibiotics — First and Fast

• Target: antibiotics within 60 minutes of arrival — this is the single most actionable factor affecting mortality
• Do not delay antibiotics for CT, LP, or intubation
• Draw blood cultures → then give antibiotics immediately
• LP can be deferred until stabilization if critically ill
• CSF sterilization begins within 15 min–2 hours for meningococcal meningitis, 4–10 hours for pneumococcal

Empiric Regimen (Adults)

2. Dexamethasone — Before or With First Antibiotic

• 0.15 mg/kg IV q6h × 4 days (up to 10 mg per dose)
• Must be given 20–30 min before or simultaneously with first antibiotic
• Reduces mortality in pneumococcal meningitis; reduces hearing loss in H. influenzae meningitis
• Stop if Listeria is confirmed — steroids worsen outcomes in Listeria CNS infection

Ventilator Management

General Principles

• Avoid hypoxia (SaO₂ ≥94%) and avoid hyperoxia
• Avoid hypercapnia (CO₂ causes cerebral vasodilation → worsens ICP)
• Target PaCO₂: 35–40 mmHg (normocapnia) in stable patients
• Controlled hyperventilation (PaCO₂ 30–35 mmHg) only as a bridge for acute herniation — not for sustained use (causes ischemia)
• Avoid high PEEP if ICP is elevated — impairs venous drainage from the brain (keep PEEP ≤8 if ICP is concern)
• Head of bed: 30–45° elevation to facilitate venous drainage

Sedation & Analgesia

• Use agents that allow neurological assessment windows:
  • Propofol (titratable, short-acting, reduces ICP, can cause propofol infusion syndrome with prolonged use)
  • Fentanyl (analgesia, hemodynamically neutral)
  • Avoid deep paralysis unless needed for ICP or ventilator dyssynchrony
• Daily sedation holds to reassess neurological status whenever safe

Intracranial Pressure (ICP) Management

• 55.6% of bacterial meningitis patients admitted to ICU needed an intracranial device
• 44% had ICP >20 mmHg at some point during ICU stay
• 51% required CSF drainage via external ventricular drain (EVD)
• ICP monitoring + EVD are used but carry risks (intracranial hemorrhage in ~2 cases)

ICP Targets and Treatments

Hemodynamic Management

• Fluid resuscitation: Isotonic crystalloid (NS or LR) — start 20–30 mL/kg if hypotensive, reassess frequently
• Vasopressors if MAP <65 despite fluids:
  • Norepinephrine: first-line (0.05–2 μg/kg/min)
  • Dopamine: alternative (1–20 μg/kg/min)
• Target MAP ≥65–70 mmHg (higher if ICP elevated, to maintain CPP)
• Avoid large fluid boluses in patients with elevated ICP (can worsen cerebral edema)

Seizure Management

• Seizures occur in 30% of adults with bacterial meningitis — higher rate in ICU/ventilated patients
• Continuous EEG monitoring recommended in comatose/ventilated patients (non-convulsive status epilepticus can be missed)
• Levetiracetam (Keppra) preferred: 1000–3000 mg/day IV — no sedation, no hepatic induction
• Benzodiazepines for acute seizure control (lorazepam 0.1 mg/kg IV)
• Prophylactic anti-epileptics are not routinely recommended unless high-risk features

Monitoring in ICU

Complications to Anticipate in the Ventilated Patient

Prognosis in Ventilated Patients

• 50.5% had poor functional outcome at 3 months (mRS 3–6)
• 25.8% mortality
• Factors independently associated with poor outcome:
  • Age >60 years
  • Immunocompromised state
  • Delay from hospital admission to ICU >1 day
  • GCS motor component ≤3
  • Respiratory failure (OR 1.76)
  • Cardiovascular failure (OR 1.72)
• Protective factors: early third-generation cephalosporin (OR 0.54) and acyclovir (OR 0.55)

Key Takeaways for the Ventilated Meningitis Patient

1. Antibiotics + dexamethasone in the first hour — the most modifiable determinant of mortality
2. Ventilate to normocapnia; brief hyperventilation only for acute herniation
3. ICP management is active — mannitol/HTS, EVD for hydrocephalus, target CPP ≥60
4. Vasopressors to maintain MAP ≥65–70 (norepinephrine first-line)
5. Continuous EEG in comatose patients — non-convulsive status is common and missed
6. Monitor sodium — SIADH is common and worsens cerebral edema
7. Add ampicillin + acyclovir empirically until coverage can be narrowed
8. Delay to ICU admission independently worsens outcomes — escalate early