Draw up your lidocaine and place the collection tubes in

sequential order (numbers are written on the tubes,

#1-4). Connect the manometer to the stopcock. Clean the

area with Betadine-soaked handheld sponges in a circular

motion, from the site of planned puncture outward.

Include a spinal level above and below 14. Allow the area

to completely dry. Place the unfenestrated drape on the

patient's bed and the fenestrated drape (with the opening)

over the procedure site. Palpate landmarks again. Using

the 25-gauge needle, raise a skin wheal of lidocaine over

the interspace. Then, use a 20- or 22-gauge needle to

anesthetize the deeper subcutaneous tissue along the

approximate line that the spinal needle will pass. Aspirate

before injecting to make sure you are avoiding intravascular administration.

Identify your landmarks again by palpating the interspinous space with your nondominant hand. With the

.A. Figure 5-2. Decubitus position for lumbar puncture. (Reproduced with permission from Krupp MA, et al. Physician's

Handbook. 21st ed. Lange, 1 985.)

CHAPTER 5

Cauda equina

.A Figure 5-3. Anatomy of the lumbar spinal

interspaces for LP. (Reprinted with permission from

Ladde JG. Chapter 1 69. Central Nervous System

Procedures and Devices. In: Tintina lli JE, Stapczynski JS,

Cline OM, Ma OJ, Cyd ulka RK, Meckler G O, eds.

Tintinolli's Emergency Medicine: A Comprehensive

Study Guide. 7th ed. New York: McGraw-Hi ll, 201 1 .)

needle parallel to the stretcher, slowly insert in the mid ­

line aiming 10 degrees cephalad. T he needle will cross

3 ligaments (supraspinous, interspinous, and the strong

elastic ligamentum flavum) before entering the dura and

subarachnoid space (Figure 5-3). You may feel a "pop" as

you transverse the ligamentum flavum. T he bevel of the

needle should be pointed to the patient's side (left or

right) to prevent it from cutting the longitudinally oriented fibers of the dura. T heoretically, this will r educe the

risk of persistent CSF leak and subsequent post-LP headache. After inserting the needle 4-5 em or after feeling a

"pop;' remove the stylet and look for the efflux of CSF at

the base of your needle. If no fluid returns, replace the

stylet and advance or withdraw the needle and recheck.

You may have to withdraw the needle to the subcutaneous tissue and redirect it more cephalad. T he depth of

insertion before getting into the subarachnoid space

depends on the size of the patient. Never advance or

remove the needle without the stylet in place to avoid it

from becoming obstructed.

When the subarachnoid space is entered and CSF

begins to flow, assess the opening pressure. Attach the

manometer to the needle and direct the lever of the 3 -way

stopcock away from the needle to create a communication between the needle and glass column. At the point

when fluid stops flowing into the manometer, the pressure is recorded. Normal opening pressure is between

7-18 cmHp. Deposit the CSF from the manometer into

tube #1 and disconnect the manometer. In adults, proceed to collect 1 -2 mL of CSF per tube. More tubes may

be needed for additional tests or special situations

(VDRL, viral titer, Cryptococcus antigen, etc). When the

fluid has been collected in all 4 tubes, the needle is

removed with the stylet in place. T his too has been shown

to reduce the incidence of post-LP headache. T he theoretical explanation for this effect is that the stylet pushes

back any pia mater that may be sticking out from the hole

made in the dura. Any tissue in the dura puncture can act

to keep the hole from closing and result in a persistent

CSF leak.

Tubes #1 and 4 should be sent for cell counts with differential. Tube #2 is sent for protein and glucose. Tube #3

should be sent for culture and Gram stain. Patients with an

obese body habitus or with degenerative joints may present

a challenge when performing an LP. Fluoroscopy (per ­

formed by a radiologist) or the use of ultrasound may aid

in identifying the anatomical landmarks, making it possible to perform the procedure.

COMPLICATIONS

A "traumatic" LP (from injury to the dura or arachnoid

vessels) is a common occurrence, with more than 50o/o of

all LP procedures having from 1 to 50 red blood cells

(RBCs) in the CSF. T he incidence of traumatic LP may be

minimized by proper patient and needle positioning. T he

best method to differentiate a traumatic LP from an SAH

is noting that the number of RBCs significantly decrease

from tube #1 to tube #4 in a traumatic LP. Tube #4 should

have close to zero RBCs. T he presence of xanthochromia

indicates a SAH.

Spinal hematomas (epidural, subdural, and subarach ­

noid) are rare complications of LP, which are more likely to

occur in patients with coagulation disorders. Correcting

coagulation disorders (eg, Factor for a hemophiliac) is

required before LP is performed.

Herniation can occur when CSF is removed from a

patient with increased ICP from a mass, emphasizing the

importance of performing a head CT if a mass lesion is

suspected.

Post-LP headaches are the most common complication of LP and are thought to be from continued CSF

leakage through the dura at the puncture site. A post-LP

headache is observed in 20-?0o/o of patients and is more

common in young adults. Post-LP headaches are usually

fronto-occipital and may have associated nausea, vomiting, and tinnitus. In most cases, the headache begins

within 24-48 hours of the LP and is usually postural

(worse in the upright position or with valsalva maneuvers). Post-LP headaches usually last 1-2 days, but occasionally can persist up to 14 days. Treatment consists of