Management of Suspected Meningitis/Encephalitis: Timing of Antibiotics and Lumbar Puncture
The correct answer is D: Administer dexamethasone and then broad-spectrum antibiotics and acyclovir. However, the critical nuance is that the timing depends entirely on whether the patient can undergo immediate lumbar puncture (LP) or if there are contraindications requiring delay.
Clinical Decision Algorithm
Step 1: Assess for Severe Sepsis, Shock, or Rapidly Evolving Rash
If ANY of these are present:
- Give antibiotics immediately after blood cultures (within 1 hour of arrival) 1
- Do NOT perform LP at this time 1
- Delays in antibiotics increase mortality 1, 2
If none are present, proceed to Step 2.
Step 2: Assess for LP Contraindications
Check for these specific contraindications before LP: 1, 2
- Focal neurological signs
- Papilledema
- Continuous or uncontrolled seizures
- Glasgow Coma Scale (GCS) ≤ 12
- Respiratory or cardiac compromise
- Coagulopathy or bleeding diathesis
If contraindications exist:
- Obtain blood cultures immediately 1, 2
- Start antibiotics immediately after blood cultures (do not wait for imaging or LP) 2, 3
- Obtain CT scan only if indicated by contraindications 1
- Perform LP after imaging if safe, ideally within 4 hours of starting antibiotics 1, 3
If NO contraindications exist:
- Obtain blood cultures 1
- Perform LP within 1 hour of hospital arrival 1, 2
- Start treatment immediately after LP and within the first hour 1
- If LP cannot be performed within 1 hour, start antibiotics immediately after blood cultures 1
Recommended Treatment Regimen
For suspected bacterial meningitis with encephalitis consideration: 2, 4, 5
- Dexamethasone 10 mg IV (give before or with first antibiotic dose) 4, 5
- Ceftriaxone 2g IV or cefotaxime (third-generation cephalosporin) 4, 5
- Vancomycin (to cover resistant Streptococcus pneumoniae) 4, 5
- Acyclovir (to cover herpes simplex virus encephalitis empirically) 5
Critical Time Points
The UK Joint Specialist Societies guidelines establish these non-negotiable timeframes: 1, 2
- Blood cultures: Within 1 hour of arrival
- LP: Within 1 hour if no contraindications
- Antibiotics: Within 1 hour (after LP if possible, or immediately after blood cultures if LP delayed)
- If antibiotics given first: Perform LP within 4 hours to maximize culture yield 1, 3
Why Option A is Wrong
Waiting for LP to start antibiotics is dangerous and increases mortality. 1, 2 While CSF culture yield drops significantly after antibiotics (73% positive if LP done within 4 hours vs. 11% if later, and 0% after 8 hours), delaying treatment for diagnostic yield is never justified when bacterial meningitis is suspected. 3 Even after antibiotics are started, LP within 4 hours still has reasonable culture positivity. 3
Why Option C is Wrong
Routine neuroimaging before LP delays treatment and is not indicated unless specific contraindications exist. 1, 2 The guidelines explicitly state that patients should NOT have neuroimaging before LP unless there are clinical indications suggestive of brain shift. 1 Unnecessary CT scans are a major cause of treatment delays and reduced culture yield. 3, 6 If imaging is truly needed, antibiotics must be started first. 6
Common Pitfalls to Avoid
- Never delay antibiotics waiting for LP or neuroimaging - this significantly increases mortality 2, 3, 6
- Do not order routine CT scans - only 20% of patients who received CT scans actually had contraindications to immediate LP 3
- Do not be falsely reassured by normal vital signs - patients with meningitis can deteriorate rapidly regardless of early warning scores 1
- Do not forget dexamethasone - it must be given before or with the first antibiotic dose to reduce neurological complications in pneumococcal meningitis 4, 5
- Do not forget acyclovir - empirical coverage for HSV encephalitis is critical as it can be fatal with 50% of survivors having long-term sequelae 5