Patient Position - Lateral Decubitus

The standard patient position for the LP is the left lateral decubitus position if the operator is right handed. The patient should be on a firm but comfortable surface so that spine remains straight. Pay special attention to the alignment of the shoulders and the hips. They should be straight up and down and perpendicular to the mat. Then have the patient flex the knees to the chest and head to the chest. Recheck the alignment of the spine and make sure that the shoulders and pelvis are perpendicular to the mat. Identify the iliac crests and draw an imaginary line between them which will identify the spinous process of L₄. Just above the L₄ process will be the L_3-4 interspace and just below will be the L_4-5 interspace. Either one are acceptable for the procedure.

Alternate Position - Sitting Position

If the lateral decubitus position cannot be used or if the LP attempt is unsuccessful in that position, then an alternative position is to have the patient in a sitting position, leaning forward with his arms on a table and his head resting on his arms. Make sure the spine is straight. Identify landmarks and establish the appropriate interspace. Make sure the needle is in the midline and aimed at the umbilicus. The bevel of the needle should be parallel to the spine or in other words, the lumen of the needle should be facing toward the side of the patient.

Location of Landmarks

With the patient in the left lateral decubitus position palpate for the iliac crests and draw an imaginary line between them. Identify the L_3-4 interspace and make sure the spine is straight. Warn the patient that she will feel some pressure as you palpate for landmarks.  Open up the interspace by having the patient flex her knees to the chest and her head to the chest. Make sure she is comfortable by having a pillow for her head to rest on. Make sure the shoulders and the pelvis are still perpendicular to the mat. Reestablish the desired interspace. Some operators will use the tip of a ball point pen to make an indentation at the spot so they can more easily identify the interspace after draping and prepping the patient. You can see the indentation at the L_3-4 interspace in this patient.

Tray Set Up Part 1: Tray, Gloves, and Drape

Open the LP tray in a fashion that exposes the contents but still maintains their sterile condition. This is demonstrated in the movie.

Select the proper size of gloves and put them on in a sterile fashion as demonstrated in the movie.

Tray Setup Part 2: Monometer and Stopcock

On the tray is a monometer that is usually in two pieces. The first piece is marked to 39 cm of water and the extension goes up to 55 cm of water. Attach the two pieces of the monometer together. A normal opening pressure should be 18 cm or less.

Tray Setup Part 3: Tubes, Lidocaine, Needle, and Betadine

There are 4 CSF tubes that are provided with the tray. Each tube is numbered. I like to unscrew the caps so that the tubes are easy to fill and handle during the CSF collection. Place the tubes upright in the wells provided and in numerical order so that they can be filled in the proper sequence. This is important because tube1 should be sent for glucose and protein, tube 2 for culture and gram stain, tube 3 for cell count and tube 4 for any other studies or to save if additional studies are needed.

After the tubes are placed in order, draw up the lidocaine. Open the 1% lidocaine bottle by braking off the top of the container. Use a 3 cc syringe to draw up 2 cc of lidocaine using the 1 ½  22 gauge needle. Express out all of the air so there is no air in the syringe. Change needles on the syringe to the ½ inch 25 gauge needle used for the initial subcutaneous injection of lidocaine.

Inspect the spinal needle and make sure the stylet is in place. A styletted needle is always used because an open needle could cut off a small piece of epidermis as it is introduced through the skin and carry it into the subarachnoid space. This could result in an epidermoid tumor.

Drape and Prep

Sponges that are dipped in betadine are used to prep the skin so this area is sterile.

Local Anesthesia

Use a small gage short needle to create a subcutaneous wheal of lidocaine so that the skin will be anesthetized. After the wheal is formed then withdraw the needle. Wait a few seconds to allow the lidocaine to numb the skin then introduce the needle into the center of the wheal and numb the underlying dermis. Withdraw the needle and replace the needle with a longer needle, usually a 1 ½ inch small gauge needle. Introduce this needle at the center of the wheal and slowly advance the needle while injecting the lidocaine to anesthetize deeper tissue layers. Draw back on the syringe to check for blood return before each injection of lidocaine to make sure that you not in a vein.

Needle Selection- Cutting Edge Spinal Needle

The cutting edge needle is a beveled needle that cuts though the tissue as the needle is advanced. The smallest possible yet adequate gauge needle should be used to reduce the incidence of post-LP headache. A 22 gauge 3 ½ inch needle is a typical needle to use for an average sized adult. A 22 gauge 1 ½ inch needle is available for use in infants and young children.  The stylet should remain in the needle as the needle is being advanced. Once CSF is obtained the stylet is removed and the stopcock is attached to the hub of the needle and the opening pressure is measured.

Needle Selection- Atraumatic Pencil Point Spinal Needle

This type of a needle has the advantage of using a blunt or non-cutting point so that the dura and ligaments are spread rather than cut as the needle is used for the LP. Because of this, the incidence of post-LP headache is about 50% less than when a cutting edge needle is used (12% vs. 24 %). The atraumatic pencil point spinal needle requires the use of an introducer needle. The introducer needle has a cutting edge and is used to get through the tissue layers from the skin to the interspinous ligaments. The styletted pencil point needle is then threaded through the introducer needle and advanced through the remaining ligaments and dura into the subarachnoid space. The stopcock is attached to the hub of the spinal needle. When the LP is completed the spinal needle and introducer needle are removed together as one unit.

Insertion of Needle - Atraumatic Pencil Point Needle

Insert the introducer needle in the mid line of the L_3-4 interspace at the center of the wheal made by the lidocaine  paying particular attention to the correct alignment of the needle. The needle should be in the same plane as the spinous processes aimed at the correct angle which is a cephalad angle of about 15 degrees which is about the angle if you were aiming the needle at the umbilicus. Once the introducer needle is through the skin, dermis and interspinous ligaments, then thread the styletted pencil point needle though the introducer needle and slowly advance the needle through the ligamentum flavum and dura into the subarachnoid space. As you advance the needle stop and remove the stylet occasionally and check for CSF return so that you don’t advance the needle beyond the subarachnoid space. Once CSF is obtained then attach the stopcock to the hub of the needle and measure the opening pressure.

Insertion of Needle - Cutting Edge Needle

The cutting edge needle is introduced at the center of the wheal made by the injection of the lidocaine at the L_3-4 interspace. The bevel of the needle should be parallel to the spinal cord which means the beveled edge of the needle is facing the operator. The needle should be in the same plane as the spinous processes aimed at the correct angle which is a cephalad angle of about 15 degrees which is about the angle if you were aiming the needle at the umbilicus. Advance the needle slowly checking occasionally for CSF return by removing the stylet and watching for CSF in the hub of the needle. Sometimes you may feel a pop as the needle penetrates the dura but this doesn’t always occur. If the CSF flows slowly or the CSF flow stops, the needle may be rotated 90 degrees which may improve the flow. If this doesn’t work then try advancing the needle slightly or pulling it back slightly in order to change the position of the needle in the subarachnoid space. Once CSF is obtained then attach the stopcock and measure the opening pressure.

Monometer- Opening Pressure

Once CSF is obtained then attach the stopcock with the monometer in place to the hub of the needle. Turn the handle of the stopcock toward the operator so that CSF flows up the monometer. Have the patient relax her flexed position so the knees are not tight up against the abdomen. Increased intra-abdominal pressure will elevate the CSF pressure measurement. Crying will also elevate the CSF pressure. The CSF should have a pulsating quality to it and once the CSF stops rising in the monometer there should be some fluctuation of the CSF level with respirations. The level where the CSF ceases to rise when the patient is totally relaxed is the opening pressure. For this patient the opening pressure is 11 cm. A normal opening pressure is less then 18 cm of water. The opening pressure should be recorded in the procedure note.

CSF Collection

After the opening pressure is obtained, start collecting the CSF by turning the handle of the stopcock. By turning the handle toward the patient, the CSF in the monometer tube can be collected in the first tube, then turn the handle toward the monometer and CSF will flow from the patient into the tube. Carefully collect all the CSF in the tubes starting with tube 1. Collect approximately 2cc in each tube. Sometimes the CSF will drip very slowly, be patient. Once one tube has the desired amount of CSF then quickly place the next tube under the hub to catch the next drop. Screw on the cap of the tube before placing it on the LP tray so that there is no chance of accidentally spilling the CSF. 

Monometer - Closing Pressure

After the CSF has been collected and before the needle is withdrawn, a closing pressure can be obtained. Obtaining a closing pressure is indicated when it is important to know how much the CSF pressure has been lowered by removing CSF during the LP such as when treating pseudotumor cerebri. Turn the stopcock handle toward the operator and the CSF is then directed into the monometer. The closing pressure is noted when the CSF stops rising in the tube. In this patient, the closing pressure is 7.5 cm of water. The closing pressure is recorded in the procedure note.

Withdrawal of Needle

With the stopcock in place, turn the handle toward the patient and withdraw the needle. Apply pressure to the puncture site until any bleeding stops. You can then wash off the betadine from the surrounding skin and apply a bandaid over the puncture site.

Inspection of CSF

After the LP, the appearance of the CSF in the tubes should be noted and described in the procedure note. Normal CSF is crystal clear. Abnormal appearance includes cloudy, yellow, pink, or red. Any clearing between the first and last tube and any sediment in the tubes should be noted.

Tray Clean up

After the LP is completed then collect all the needles from the tray without replacing any caps and dispose of them in an appropriate safe container such as a “sharp box”. Make sure the caps are tightened on all the tubes and the tubes are appropriately labeled with the patient’s name and identifying information. Write the orders for the laboratory studies to be done on the CSF and make sure that the CSF gets to the lab as soon as possible. Dispose of the LP tray in the appropriate receptacle.

Review of the LP Technique

This section is a quick review of the LP procedure.  The first thing to do is have the patient lying on their side with legs and neck flexed with shoulders and hips perpendicular to the mat. This opens up the interspace. Then identify the L_3-4 interspace by drawing a line from the top of the iliac crests. Drape and prep the patient in a sterile fashion. Use 1% lidocaine for local anesthesia. Use a styleted spinal needle. A pencil point needle and smaller gauged needle are less likely to cause a post-lumbar puncture headache. If using a cutting edge needle make sure the bevel is facing up. The needle should be pointing towards the umbilicus (this will give you the needed 15 degree angle so you are parallel to the spinous processes). Advance the needle slowly checking for CSF return.
    
When the needle is in the subarachnoid space, attach the 3-way stopcock with the manometer in place. Have the patient relax the tightly flexed position they have been in and then obtain the opening pressure. Normal opening pressure is less than 180-200 mm of water. After the opening pressure is obtained, collect the CSF in 4 tubes with approximately 2 ml in each tube. If special studies are going to be done, make sure you have collected an adequate amount of CSF. The tubes should be sent for the following studies:
Tube #1- glucose and protein
Tube #2- culture and gram stain
Tube #3- Cell count
Tube #4- for special studies and to save for addition studies if needed

Lumbar Puncture Procedure Note