Why are mannitol and dexamethasone given after a lumbar puncture?

Mannitol and Dexamethasone After Lumbar Puncture: Indications and Evidence

Mannitol and dexamethasone are not routinely recommended after lumbar puncture and may potentially be harmful in most clinical scenarios. 1, 2

Post-Lumbar Puncture Complications

Post-Dural Puncture Headache (PDPH)

• PDPH affects up to 35% of patients following lumbar puncture, typically developing within 3 days 1, 2
• Characterized by orthostatic headache that worsens when upright and improves when lying flat 2
• Caused by sustained CSF leakage from the dural tear created during the procedure 1, 2

Elevated Intracranial Pressure

• Lumbar puncture can precipitate brain herniation in patients with elevated intracranial pressure 1
• Risk of brain herniation after lumbar puncture has been reported in approximately 6-11% of patients with elevated intracranial pressure 1

Evidence Against Mannitol After Lumbar Puncture

• Mannitol has no proven benefit for controlling increased intracranial pressure after lumbar puncture and is not routinely recommended 1
• Mannitol works by increasing plasma osmolarity, inducing movement of intracellular water to extracellular and vascular spaces, thereby reducing intracranial pressure 3
• However, this mechanism is not appropriate for post-LP headache, which is caused by low CSF pressure rather than elevated intracranial pressure 2
• Research on mannitol for post-lumbar puncture pain shows no significant effect on postoperative low back and leg pain compared to controls 4

Evidence Against Dexamethasone After Lumbar Puncture

• Dexamethasone should be avoided for controlling increased intracranial pressure after lumbar puncture 1
• Studies show dexamethasone does not have a protective effect against PDPH and may even increase its incidence in the first 24 hours 5
• A randomized controlled trial demonstrated that prophylactic administration of 8 mg dexamethasone did not prevent PDPH and potentially increased its incidence 5
• Rare but serious adverse effects of dexamethasone have been reported, including cerebral vasculitis in a case of pneumococcal meningitis 6

Appropriate Management of Post-LP Complications

For Post-Dural Puncture Headache:

• More than 85% of post-LP headaches resolve without specific treatment 2
• For mild cases, caffeine or paracetamol/caffeine can provide symptomatic relief 2
• For severe and persistent headache, epidural blood patch is the most effective treatment 2

For Elevated Intracranial Pressure (in cryptococcal meningitis):

• If CSF pressure is ≥25 cm of CSF with symptoms of increased intracranial pressure, relieve by CSF drainage via lumbar puncture 1
• Reduce opening pressure by 50% if extremely high or to a normal pressure of ≤20 cm of CSF 1
• For persistent pressure elevation with symptoms, repeat lumbar puncture daily until pressure and symptoms stabilize 1

Prevention of Post-LP Complications

• Use atraumatic (pencil-point) needles rather than conventional needles 1
• Atraumatic needles separate and dilate dural fibers rather than cutting through them, resulting in smaller openings 1
• Use smaller gauge needles when possible 2
• Orient the bevel of the needle in a transverse plane 2
• Replace the stylet before withdrawing the needle 2
• Minimize the number of attempts at dural puncture 2

Special Circumstances: When Steroids May Be Indicated

• In bacterial meningitis, dexamethasone may be indicated as adjunctive therapy with antimicrobials, but this is unrelated to the lumbar puncture procedure itself 1
• For immune reconstitution inflammatory syndrome (IRIS) with CNS inflammation and increased intracranial pressure, corticosteroids may be considered 1

In conclusion, neither mannitol nor dexamethasone is routinely indicated after lumbar puncture for management of common complications like PDPH. Their use should be limited to specific clinical scenarios unrelated to the lumbar puncture procedure itself.