Episode 81: Bacterial meningitis with Casey Albin

We talk about diagnosis, treatment, and subsequent care of the patient with bacterial meningitis, with Emory neurointensivist Casey Albin, MD (@caseyalbin).

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Takeaway lessons

Many septic patients have altered mental status, but suspicion should be raised for CNS infection when there is also: headache, photophobia, vomiting, or any possibility of seizure activity.
Meningitis and encephalitis are separate entities usually involving different organisms, different imaging findings, and with different prognostic implications and downstream complications. However, at the early diagnostic stage, they can be largely lumped together.
Empiric antimicrobials must consider CNS penetration. Piperacillin/tazobactam (ie Zosyn) has very little. Ceftriaxone is better. Cefepime is fine, although the prospect of cefepime neurotoxicity may make neurologists leery; ceftazidime is fine too. Add vancomycin (not necessarily for MRSA but for resistant Strep pneumo), acyclovir (for HSV), and a liberal approach to adding ampicillin for Listenia for anybody older, immunocompromised, or in the midst of an outbreak.
Dexamethasone has been shown to reduce hearing loss after Strep pneumo meningitis. If suspicion for meningitis is strong early, it’s reasonable to give early (before or concurrent with antibiotics). It’s probably not worth giving >24 hours later.
The main benefit of lumbar puncture is to allow stopping or narrowing antimicrobials without treating with the entire empiric cocktail for a full two weeks. (There is also the chance of identifying a resistance organism.)
Ideally, LP is done before antimicrobials. However, if non-culture-based diagnostics are available such as PCR panels, successful diagnosis can often occur even after antibiotic administration. It’s worth doing the LP even if late and no PCR is available, as the signature of protein, glucose, etc will often still be useful. (At least, up front in a patient who might have CNS infection, avoid creating new obstacles like loading them with anticoagulation, antiplatelets, low molecular weight heparin, etc.)
Most patients will already have a CT head performed before LP is considered, making the question of whether this is necessary (to assess risk of downward herniation) fairly moot. However, if not, it should probably be done prior to LP in anyone with an altered level of consciousness.
Order from all CSF: Gram stain and culture, cell counts (first and last tubes), glucose, protein, and HSV PCR. (VZV generally does not cause clinical meningitis per se, usually causing a meningitis vasculitis, e.g. in someone with small-vessel strokes.) If available, order PCR arrays too, although some centers may not run it unless the CSF WBC count is elevated (e.g. >5). In a patient with any immunocompromise, test for cryptococcus as well. Other immunosuppressed testing is case-specific.
Always measure opening pressure. This is not accurate in a patient sitting up. While technically possible to puncture a patient sitting up, then rotate them with assistance to lay flat, it’s not easy or elegant. In a sick patient, just do the LP laying down.
Remember that opening pressure is measured at the bedside in centimeters of water, but should be converted to millimeters of mercury to be clinically applicable.
Draw at least 20 cc of CSF in all cases. If opening pressure is high (and CT not concerning), fill the four tubes (~36 cc) and measure the closing pressure. Few patients are harmed by draining <40 cc. Draining >40-50 can create some risk for herniation or hemorrhage (eg small subdural hemorrhage) and should not be done thoughtlessly.
Meaningfully elevated CSF protein should not just be “high,” but should exceed the patient’s age.
Any meningitis patient with an altered mental status should at least have a spot EEG, and possibly long-term EEG depending on the findings.
Any meningitis patient with a high opening pressure on LP, who is sufficiently obtunded to be intubated, should be considered for invasive ICP monitoring (e.g. EVD), if available. Otherwise, close monitoring for ICP crisis with neuro and pupil checks and serial CT scans.
Treating high ICP in meningitis with EVD or lumbar drain is often appropriate.
Any neurologic deterioration after antibiotics and other initial care is very likely either seizure or ICP crisis. These are fixable patients; diagnose and treat these complications aggressively.
Transcranial doppler may be a useful non-invasive screen for elevated ICP, by revealing a high-resistance waveform (high pulsatility index) as ICP increases.