Lumbar puncture in infants and children — branching viva

Opening question

This 4-month-old febrile infant with irritability and a full fontanelle needs a diagnostic lumbar puncture. Walk me through the structured pre-LP assessment you would perform, and tell me what would make you image before the LP rather than proceed. [1]

Branch 1 — positioning, needle and the opening pressure

You have decided the LP can proceed. Describe the position and the needle you would choose, and tell me exactly how you would obtain a reliable opening pressure — including the conditions under which you would discount the reading. [2] [3]

Branch 2 — suspected bacterial meningitis and the antibiotics-first rule

Suppose instead this infant arrives in septic shock with cold peripheries and a capillary refill of 4 seconds. What is the order of priorities, and what is the rule on antibiotics relative to the LP? Defend it. [4]

Branch 3 — interpreting the CSF, including a traumatic tap

The LP yields a frankly blood-stained CSF that clears between the first and fourth tubes. How would you interpret this, what correction would you apply to the white-cell count, and which results would still stand on their own? [1]

Closing — post-dural puncture headache

Two days later the child's older sibling, who also had an LP, returns with a postural headache. What is the natural history, what is the first-line management, and when would you refer for an epidural blood patch? [2]