Lumbar Puncture Basics

A lumbar puncture (sometimes called a spinal tap) is a procedure that involves the insertion of a needle into the space between two lumbar vertebrae. The needle punctures the dura to enter the subarachnoid space so that the MD or APRN can measure the cerebrospinal (CSF) pressure and obtain a sample for evaluation.

Lumbar punctures (LP) are utilized to diagnose a variety of conditions affecting the central nervous system, with meningitis being the most common. Other conditions include Guillain Barre, cancers of the spinal cord or brain, and multiple sclerosis. While lumbar punctures are mainly used as a diagnostic tool, they can be utilized to administer certain medications directly to the spinal fluid, such as chemotherapy.

What is cerebrospinal fluid (CSF)?

Cerebrospinal fluid is the watery substance that fills the hollow space between the arachnoid membrane and the pia mater in the brain and spinal cord. It is produced by the choroid plexus in the ventricles.  In addition to providing the brain and spinal cord with nutrients, CSF also acts as a cushion to protect the delicate structures from injury.

What are the normal qualities of CSF?

• Color: Clear and colorless
• Opening pressure: 10 to 20 cm H20
• Glucose: approx 60% of serum glucose
• Protein: 15 – 45 mg/dL (may increase up to 70mg/dL in children and elderly adults)
• WBC (varies by age): 
  • 0 to 30 cells/μL (neonate)
  • 0 to 20 cells/μL (child age 1-5)
  • 0 to 10 cells/μL (child age 6-18)
  • 0 to 5 cells/μL (adult)
• RBC: None

How is a lumbar puncture performed?

A lumbar puncture is performed with the patient lying on their side with their knees drawn up. The practitioner numbs the area with lidocaine and then inserts a hollow needle into the subarachnoid space between L2 and L3, L3 and L4, or between L4 and L5.

To measure the opening pressure, the MD attaches a manometer to the hollow needle. Higher pressures are associated with conditions like meningitis, cerebral edema, and Guillain-Barre (among others). Once the opening pressure is obtained, the practitioner lets the fluid flow from the manometer into the collection vial under gravity. If additional CSF is needed, the manometer is removed and the fluid drains from the patient into the collection tube passively.

The needle is then removed and the area is dressed.

What are the contraindications for a lumbar puncture?

Lumbar punctures are avoided in cases where the skin at the insertion site has an infection, as this could introduce bacteria into the CNS. They are also avoided or used with extreme caution in patients with increased ICP who are at risk for cerebral herniation, patients with bleeding disorders (including thrombocytopenia and current anticoagulant therapy), and patients with a suspected spinal epidural abscess.

What are the most common complications of lumbar puncture?

The most common adverse effect following lumbar puncture is headache, which is often referred to as a “spinal headache.” Though the exact pathophysiology of the headache is not fully understood, it is considered to be due to CSF leaking into the site where the lumbar puncture was performed. This temporarily reduces CSF pressure and CSF volume. It is thought that this reduces the amount of “cushion” around the brain and the pain-sensitive meninges. Additionally, it is thought that the decreased CSF volume triggers adenosine receptors that cause cerebral vasodilation, which puts pressure on pain-sensitive structures in the brain. 

Spinal headaches occur in about 10 to 30 percent of patients and may be accompanied by other symptoms including dizziness, nausea, vomiting, visual changes, neck stiffness, and tinnitus. In most cases, the headache improves over time as the choroid plexus replaces lost CSF volume. Since the headache is worse in an upright position, keeping the patient supine is recommended. In cases where the headache persists, the patient may need an epidural blood patch to seal off the puncture site in the dura.

Additionally, about one third of patients experience low back pain for several days after the procedure that may or may not be accompanied by numbness or tingling in the legs.

What are the most serious complications of lumbar puncture?

Serious complications after lumbar puncture include infection, bleeding and spinal hematoma, subdural hematoma, and cerebral herniation.

Infection – Though not common, infections after lumbar puncture can occur when strict aseptic technique is not followed. For example, performing an LP through the site of a skin infection could result in bacteria getting introduced into the CNS. Additionally some studies have shown that post-LP infection can result from aerosolized secretions from personnel present during the procedure (a reminder of why wearing a mask in any procedure area is important!)

Bleeding – Though rare, bleeding after lumbar puncture can create a hematoma that compresses the spinal cord. The risk is higher in individuals with a bleeding disorder or thrombocytopenia, and in those who receive anticoagulant therapy before or directly after the procedure. 

Prior to performing the lumbar puncture, the MD will likely order interventions to correct the coagulopathy. For example, a patient with thrombocytopenia may receive a platelet infusion prior to the procedure. In another example, if the patient is on a heparin infusion, the MD will write orders to hold the infusion for a certain period of time prior to the puncture.  If the patient is taking an oral anticoagulant, they will be instructed to stop taking it prior to the procedure. Depending on the medication, this could range from 48 hours to seven days.

If the patient does develop a spinal hematoma, the treatment is quick surgical intervention to remove the blood and relieve compression on the spinal cord.

Subdural hematoma – Though not common, subdural hematomas can occur after lumbar puncture. If your patient has an unrelenting headache or shows signs of altered LOC or neurological status, always report these to the MD as it could be a sign of a serious complication. 

Cerebral herniation – This is, by far, the most serious complication of a lumbar puncture. To help avoid this, lumbar punctures are often avoided in cases of ICP where herniation is a risk or in cases where the ICP is suspected to be due to cerebral edema, obstructive hydrocephalus or a space-occupying lesion. Again, any change in LOC or deterioration in neurological status warrants an immediate call to the physician.

How do you prepare the patient for lumbar puncture?

Prior to the procedure, the patient may receive pre-procedure medication to reduce anxiety so the patient can remain immobile during the procedure (this is especially useful in children and in patients with dementia who may not be able to consistently follow instructions. Additionally, analgesics may be utilized pre-procedure to lessen pain during and after the procedure.

As the nurse, it is your responsibility to ensure the pre-procedure checklist is complete. This includes things like ensuring the consent form has been signed, validating the patient’s last PO intake and ensuring the patient voids prior to the procedure. 

Assist the patient into the proper position, which is the lateral recumbent position with knees drawn up to the chest. If this position is not obtainable, a sitting position with the upper body leaning forward may also be used though it can skew CSF opening pressure result.

During the procedure, monitor the patient for tolerance to the procedure and signs of any complications such as severe pain or lightheadedness.

How do you care for a patient after lumbar puncture?

In addition to monitoring vital signs, key assessments and interventions include:

• Assess for headache and, if present, pain level before and after treatment.
• Maintain the patient in a flat, supine position for one to four hours to reduce leakage of CSF. Lying flat also helps relieve the discomfort of a spinal headache.
• Inspect the injection site for signs of bleeding, edema and CSF leakage.
• Monitor your patient’s neurovascular status by assessing movement and sensation of lower extremities.
• Monitor your patient’s neurological status and immediately report any changes, including changes in LOC.
• Promote hydration or provide IV fluids to reduce the risk of post-procedural headache. 
• Administer pain medication as needed for headache.

What do you teach the patient/caregiver about lumbar puncture?

• Spinal headaches can persist for 24 to 48 hours up to a few days post procedure and may be exacerbated in an upright position. Oral pain relievers, hydration, caffeine, and lying down may help.
• Limit acetaminophen to 3 grams per day in adults, less if the patient has concurrent hepatic or renal impairment. 
• Avoid the use of aspirin or ibuprofen for pain relief, as these can increase the risk of bleeding.
• Avoid soaking the puncture site until cleared by the physician. This includes no baths, hot tubs, swimming pools, or other bodies of water.
• Report any concerning symptoms to the healthcare provider immediately. These can include drainage at the injection site, inability to urinate, a persistent headache, persistent back pain, numbness/tingling in the extremities, lightheadedness, nausea, vomiting, visual changes, alterations in LOC, and changes in neurological status.

You can review Lumbar Punctures again while you’re on the go in episode 289 of the Straight A Nursing podcast. Tune in wherever you get your podcast fix, or straight from the website here.

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