Indications

Infection:

Bleeding into the CSF

  • E.g. sub-arachnoid haemorrhage

Inflammation in the brain / spinal cord / CSF

To administer local anaesthetic / or therapeutic agent (e.g. in chemotherapy)

Contraindications

  • Raised ICP! – never perform lumbar puncture when there is a raised ICP. By removing fluid from the spinal canal, you lower the pressure in this area. The high pressure within the cranium may then cause herniation of the brainstem through the foramen magnum.
    • The one exception is benign raised ICP – which is usually in young women.
    • Symptoms of RICP: headache, impaired consciousness, ↓pulse ↓BP (late stage compensation might make ↓BP)
    • If you suspect RICP, then send for CT instead of lumbar puncture.
  • Coagulopathy
  • Local infection at site of needle insertion
  • No consent!

Complications

  • Headache – very common, and usually benign. Can be managed with basic analgesia, and tell the patient to take onboard fluids. Patients can be given an infusion if necessary.
    • Can often be avoided if the patient lies down for 2 hours after the procedure
    • Persistent headachecan indicate CSF leak from the puncture site. Is often self-limiting.
  • Parasthesia – may be felt during the procedure as the spinal needle comes into contact with nerve roots or nerves of the cauda equina. May feel uncomfortable during the procedure, but usually cause no lasting damage
  • Serious complications are very rare, but can include:
    • Permanent nerve damage (mainly manifested as parasthesia), or even more rare, paraplegia

Normal values

  • Protein – 40g / dl
  • Cell count <4-5
  • Red cell countdepends on how much blood was lost during the procedure!
  • Pressure<20cm
  • Glucose – 2/3 of serum glucose

Procedure

Gather your equipment

Small needle and syringe to inject lidocaine – local anaesthetic.
  • Toxic dose of lidocaine:
    • 3mg/Kg, OR
    • 7mg/Kg with adrenaline

Spinal needle with which to perform the procedure

  • This needle actually is made up on two needles, one inside the other. This arrangement prevents a bore of skin and other subcutaneous structures becoming lodged in the inner needle – thus preventing you from getting a sample of fluid.

Location

  • ask the patient to lay on their left hand side, and bring their knees up to their chest, as much is as comfortable.
  • expose the patient’s back
  • Find the posterior superior iliac spine, on both sides
  • Imagine a line between the two – this is called Tuffier’s line.
  • Find the spinous process that lies on this line. This is roughly usually about L3! Palpate into the space below this spinous process. This is the site at which you are going to enter the CSF!Lower than this too low!

Administer Lidocaine

  • Raise a bleb on the skin, then go in slightly deeper, and use the rest of the solution
  • Leave to act for 2-3 minutes before performing the rest of the procedure

Accessing the CSF

There are 5 basic layers that your needle is going to traverse:
  • Skin
  • Fat
  • Ligaments
    • Supraspinous ligaments
    • Infraspinous ligaments
    • Flavum (‘yellow’)
  • Dura
  • CSF
Knowing the layers will help you know where your needle is.
  • Put your thumb on the spinous process you found earlier. You know that you are going to insert your needle just below this.
  • Gently advance the needle. You may be able to feel the needle pass through the individual layers. When you reach the ligaments, you will feel some resistance, this is normal. Press gently to advance the needle through the ligaments. You will feel the needle suddenly ‘give’ as you pass through the ligaments and dura, and you will now (hopefully!) be in the CSF.
  • Don’t go to far, or you can end up scraping on spinal bone
  • You can now withdraw the ‘stylet’ from the middle of the needle, and CSF should begin to flow out of the end of the needle.
  • Remember that the procedure is often very painful for patients!
  • Collection of fluid
  • You should collect about 15 drops for each sample bottle
  • Don’t forget to measure the pressure before you take a sample, if necessary
  • the pressure is measured with a manometer
  • When measuring the pressure it is very easy to get false readings. Allow the reading time to settle, and ask the patient to cough when the reading has come to rest, as this can readjust the reading to the correct level

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