Thursday, 22 February 2007

Lumbar Punctures-- Advice from B

If you already know how to do a perfect lumbar puncture (LP) procedure then great!! However, many first year doctors both here and in the UK have great difficulty in performing this procedure, in some cases because they have not had much experience and also tuition may not have been optimal.

The following is my way of performing an LP that should hopefully help junior doctors get it right in the end.

Firstly, does the patient actually need a lumbar puncture?? Is meningitis suspected or an SAH?? Does the patient have raised intracranial pressure. You should be checking for raised intracranial pressure in such circumstances by monitoring pulse and blood pressure looking for a Cushing's Reflex (low pulse, high blood pressure) and looking for papilloedema in the fundi and of course any NEW focal neurology.

If uncertain, then CT scanning should be performed to obtain images to try and rule out raised ICP.

If the patient does have raised ICP then you should not do an LP because by decompressing the pressure within the subarachnoid space from below with an LP needle can precipitate cerebellar-brainstem herniation and you then have a decerebrate patient!!

If you have a meninigitis case, then treating with antibiotics is the most important thing you can do, and if you want to get confirmation, then this can be done through obtaining blood cultures, throat and nasal swabs immediately, and PCR of CSF at a later date once signs of pressure have reduced.

So, if the patient does not have raised ICP it is safe to proceed with an LP unless the patient is on warfarin. An INR of less than 1.5 is usually safe for doing proecedures. If raised above this, and it is essential to do an LP, then the INR can be reduced by FFP in the acute setting.

I do not consider aspirin or other anti-platelet agents to be an absolute contra-indication as although they prolong the bleeding time, they do not affect the intrinsic and extrinsic coagulation pathways. More over the risk to benefit ratio tips towards doing the procedure in such scenarios.

When you have decided to do an LP please try and explain the procedure to the patient / family to obtain their permission -- this is called Informed Consent. It is necessary to explain that the procedure may feel uncomfortable although you should be using local anaesthetic in any case. You need to explain the side effects of the procedure including headache and the possibility of bleeding and introducing infection, although in my experience, this is rare. Also explain that the patient will need to usually lie flat for about 4 hours after the procedure.

Set up your tray with sterile drapes, iodine, 1% or 2% lidocaine (10ml), several LP needles, normal sized needles, a 10ml syringe, sterile gloves, a Manometer (for CSF pressure), three sterile tubes for CSF, a marker pen (not on the sterile tray), swabs and dressings.

1) Lie the patient in a Lateral position on either their Right or Left Side with their back parallel to the edge of the bed. Ask them to curl into a Foetus position-- hips and knees flexed with the knees as close to the abdominal wall as is possible. This will open the intervertebral spaces by flexing the spine.

2) Feel the top of the pelvis and then feel down to the lumbar spine. The vertical imaginary line will dissect the L4 vertebra-- this is the Intercristal Plane. Below this is the L4 intervertebral space and above is the L3 space.

3) Wherever is the most easiest place to enter use a marker pen to identify the site you wish to enter.

4) Now WASH YOUR HANDS and then put your sterile gloves on

5) Then put a sterile drape underneath the patient

6) Now, sterilise the skin with iodine in the area you want to put the needle into. Remember to also sterilise a wide field as you may have to go up higher if the space you have chosen does not work. Also, I sterilise the top of the hip and loin area so that I can find the Intercristal Plane and re-establish my land marks during the procedure. However, you may have drapes to allow just access to the designated area so you can re-establish your markings in any case.

7) You must use Local Anaesthetic during the procedure. Use 1% or 2% Lignocaine (lidocaine) and infiltrate the skin and deep muscle with a normal needle. Usually instill about 5 ml and wait until the patient cannot feel the prick of the needle on the skin. REMEMBER to ALWAYS draw back on the syringe before injecting local anaesthetic to look for blood or even CSF, because inappropriate entry into a vein or subarachnoid space can cause patients to have a seizure or cardiac dysrrhythmias.

8) Then, take your LP needle and angle the needle in the head direction and towards the umbilicus NOT perpendicular to the skin, otherwise you will hit bone. If you hit bone, then pull back and re-angle the needle upwards and advance again. If you keep hitting bone then STOP and try at a higher interspace, again have instilled local anaesthetic.

9) Once you advance the needle into the correct space, you will notice that it can go in quite deeply. You should feel some resistance to the needle and then a sudden loss of resistance that is called 'the Give'. You should now be in the subarachnoid space.

10) Now, withdraw the middle stylet of the needle and wait for the CSF. It may not come out immediately but with respiration the increased in CSF pressure should cause CSF drops to come.

11) You should now put on a MANOMETER to check the pressure in cm/mm of Water. A normal pressure is between 10-20cm of water.

12) Now take your samples of CSF, usually 10 drops, into three bottles. Label them up as 1,2 and 3 with number 1 being the first sample and number 3 being the final sample.

13) Normally 1 and 3 are sent for microscopic examination to compare white and red cell components. It is also examined for bacteria.

14) The 2nd bottle is sent for protein and glucose examination.

15) The stylet should then be reintroduced down the barrel of the LP needle and then the whole needle is removed. This is supposed to reduce post-LP headache by aiding sealing off of the dural hole created by the needle.

16) Press firmly over the entry site with a swab until any bleeding / swelling subsides and then apply a sterile dressing.

17) In my experience, the patient should lie flat for several hours although a recent JAMA 2006 article suggests that patients can ambulate soon after such a procedure. If the LP fails to produce CSF then a higher interspace level can be chosen such as the L3/L4 interspace or the L5/S1 space can also be chosen instead.

Sometimes it is necessary to do a Sitting LP. In this case the patient is sat on the edge of the bed and the doctor performs the LP from behind. The same interspace areas can be entered. This can sometimes be the only way to obtain the CSF.

Of course, if you have difficulty with a lying LP you MUST ask your Senior doctor to help you rather than repeatedly attempting the procedure.

I hope this helps and please let me know your experiences with LP procedures. I may not have covered every single problem with LP procedures here as it is a basic guide, and if you want to ask me a specific questions then please leave an anonymous entry on the blog and I will answer as soon as possible.

No comments: