• Suspected meningoencephalitis
  • Suspected subarachnoid hemorrhage despite negative CT



Risk for cerebral herniation:

  • Altered mentation
  • Focal neurologic signs
  • Papilledema
  • Seizure within the previous week
  • Impaired cellular immunity


  • Infected skin over the needle entry site
  • Coagulopathy (e.g. anticoagulant or antiplatelet use, renal failure) is a relative contraindication


  1. Prior

Prepare the Patient

  • Inform the patient about the procedure
  • Position the patient in the lateral recumbant or sitting position with the hips, knees and chin flexed towards the chest
  • Identify the L3-L4 interspace which is at the level of the posterior superior iliac crests. Identify the L2-L3 interspace and the L4-L5 interspace. Mark the interspace which is widest.


Prepare the Equipment

  • Mentally rehearse the procedure steps and assemble the necessary equipment


  1. Procedure

Sterilize and Drape

  • Don sterile gloves
  • Clean the skin over the L2-L4 area using antiseptic solution
  • Place sterile drapes around the work area



  • Administer local anesthetic under the surface of the skin at the target site +/- anesthetize the deeper tissue


Needle Insertion

  • Insert the spinal needle, with the bevel parallel to the spine, at a slightly cephalad angle, aiming towards the umbilicus, and advance the needle approximately 3-4 cm.
  • Remove the stylet and check for fluid return; if no fluid i obstained, replace the stylet, advance a few millimeters and repeat the process until CSF is obtained.
  • Attach the manometer and note the height of the fluid column. The patient’s legs should be straightened during pressure measurement.
  • Collect cerebrospinal fluid in each of 4-5 tubes (10 drops – 1 ml in each tube)
  • Replace the stylet and remove the needle
  • Apply a sterile dressing


  1. Post
  • Cerebrospinal Fluid Analysis depending on the context:
  • Cell count and differential (first and the last tube)
  • Glucose and protein levels
  • Direct microscopy, Gram stain, bacterial cultures, PCR for HSV etc.
  • Spectrophotometry if the setting of suspected subarachnoid hemorrhage