The most important thing to do is to position the patient correctly. Lay the patient on the left side, with the back parallel to the bed.
- Ask the patient to maximally flex the back to open up the spinous processes. Ensure the shoulders are square to the hips.
- Make sure the patient's back is straight and that you can feel the gaps between the spinous processes (Fig. 9).
- Feel the iliac crests, and draw across the back to the other iliac crest.
- Feel down the spinous processes until you feel a gap as close to the vertical line you have drawn as you can. This is L3–L4.
- Choose the L3–L4 space or go one space higher to L2–L3.
- Get a chair. Sit down where you will perform the procedure. Raise the bed so you are comfortable.
Fig. 9 Positioning of the patient for lumbar puncture. (Adapted from Spriging, D., Chambers, J., and Jeffrey, A. Acute Medicine, 2nd edition. 1995, Blackwell Science)
- Set up your cart with three specimen bottles labeled 1, 2, and 3. Wash your hands thoroughly.
- Open up the three-way stopcock and manometer. Connect up and be certain you know which tap opens to the manometer and closes all the others, and then close it to the manometer and open it to the "outside world."
- Check that the stylet passes through the needle properly.
- Clean over L2, L3, and L4, giving yourself a large area to work with. Administer local anesthetic at L3–L4.
- Place the spinal needle over the site of lidocaine administration, bevel facing upwards , and advance. Make sure the needle remains at a 90° angle to the skin in all planes.
- Push through several layers of tissue (Fig. 10) until you feel the needle give. Carefully remove the stylet 1–2 cm to see if you have clear cerebrospinal fluid (CSF).
- Hold the end of the needle carefully but firmly with your left hand and pull the stylet out with your right hand – cover the end of the needle with your left thumb to prevent CSF leak.
- Attach the manometer with the three-way stopcock turned to allow CSF to go straight up. Measure the CSF pressure – anything < 20 cm H2O is normal. Give it time, especially with a small needle.
- Once the pressure is measured, you can collect CSF by turning the stopcock so the spinal needle is open to you but the manometer is closed, retaining its column of fluid. Have bottle 1 ready and collect 10–12 drops of CSF. Put your thumb over the end and have your assistant take bottle 1 away and give you bottle 2. Repeat with each of the three bottles.
Fig. 10 Insertion of the lumbar puncture needle.
- For the glucose sample, collect the column of CSF in the manometer by closing the spinal needle and opening the manometer to you. Beware – this comes out very fast.
- Remove the manometer, put your thumb over the end of the spinal needle to prevent CSF loss before replacing the stylet; then remove the entire needle.
- Clean the patient's back and put a small dressing over the needle site. Move the patient onto the back and advise rest for 1 hour – local policy might advise differently on this time and can be up to 4 hours. Check with your hospital policy.
- Send bottles 1 and 3 for cell count; this will differentiate a bloody tap from blood in the CSF. Send bottle 2 for biochemistry and xanthochromia.
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If you cannot get into the epidural space, make sure you are at a 90° angle to the skin in all planes. Sometimes you will find you have aimed skyward.
If you still have no success or have hit bone, go up a space to L2–L3.
If you still have no success, sit the patient upright to perform the procedure. Again, mark out landmarks using the iliac crests and aim the needle at a 90° angle. You cannot measure the pressure but will get your samples using this method.
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