Lumbar Puncture

by Khuloud Alqaran

Case Presentation

A16-year-old male, without a known case of any medical illness, presented to the ED accompanied by his mother. His chief complaint was altered mental status. Three days earlier to his presentation, he had a fever, nausea, vomiting, and headache. The symptoms worsened over time. His mother noted that 2 weeks earlier he visited his grandmother at the intensive care unit. On physical examination, he opened his eyes once the doctor called his name; then, he said, “Where am I, what is the time?” He was moving in the bed with no neurological focal deficit. Vital signs as following: Temperature 38C, heart rate of 110/min and blood pressure of 100/45 mmHg. Nuchal rigidity was positive, and he had skin rashes over his shins as shown in the picture below.

Indications

Diagnostic

Presumption of meningitis
Presumption of subarachnoid hemorrhage (SAH).
Presumption of any syndrome such as Multiple sclerosis or Guillain-Barre
Presumption of Pseudotumor Cerebri (Idiopathic Intracranial Hypertension, IIH) by measuring the opening pressure of the Cerebrospinal fluid (CSF)

Therapeutic

Administration of anesthetic spinal agent or intrathecal drug (e.g., Chemotherapy in case of Leukemia).
Drain away excess of CSF in case of IIH

Contraindications

Absolute contraindication
- Infected skin or soft tissue at the entry site of the needle
Relative contraindication
- Increased Intracranial Pressure (ICP)
- Deranged coagulation profile (INR > 1.4 or Severe thrombocytopenia, platelet < 40,000)
Other contraindication
- Brain abscess or any space-occupying lesions (SOL)

Lumbar puncture should not be delayed for any reason in the clear indication. However, in some cases, further investigations may be needed with the CT scan. Indications for CT head prior to the LP are as follows;

Age > 60 years
Immunocompromise status
Altered mental status or presence of any neurological deficit
Any sign/symptoms of elevated ICP (e.g., headache, papilledema, or bradycardia)
History of the Central nervous system (CNS) lesion (e.g., old stroke, SOL such as tumor or abscess)
Recent seizure activity (within a week from presentation)

Equipment and Patient Preparation

Equipment

Pre-packed LP procedure kit may include the following items:
- Sterile dressing
- Sterile drape
- Alcohol Swabs
- Spinal needle size 18 gauges
- Lidocaine 1% without epinephrine
- Syringe 3mL
- 3 Way stopcock
- Monometer
- 4 plastic test tubes (numbered from 1-4)
- Syringe 10mL
- 2×2 Gauze
- Small Adhesive plaster
Extra supplies
- Non-sterile marking pen
- Chlorhexidine swabs for sterilization
- Maintain universal precautions (sterile gloves, surgical facemask, cap and sterile gown)

The spinal needle should be replaced by Styletted spinal needle size 20 or 22 gauge. However, the length should be chosen depending on the patient’s age.
- Infant 1.5in or 3.8cm
- Child 2.5in or 6.3cm
- Adult 3.5in or 8.8cm

The registered nurse or any doctor colleague to help position the patient during the procedure
Place/order CSF tests needed prior to the procedure

Patient preparation

Informed consent needs to be taken from the patient or the legal guardian.
Speak to your patient during the procedure; the patient is already anxious and can’t see what you are doing. Talk to the patient and explain what you are doing in a calm manner. For example, say: “ Now I am going to numb the site with a smaller needle; it may have a burning sensation. Please don’t move.”
Patient placed in two positions upon preference and patient condition or age
- Lateral recumbent with spine parallel to bed: in this position, the patient’s hips, knees, and chin are flexed toward his/her chest (fetal position). Analgesia, sedation or anxiolytic (e.g., benzodiazepine) can be considered if appropriate to reduce patient anxiety.
- Sitting upright with hips flexed with feet on a stool: in this position, the patient is awake and cooperative. It’s preferred in obese patients when it would ease midline localization. The patient would sit upright; his/her lumbar spine should be perpendicular to the table. His/her foot should be supported by a stool and not hanging down. A pillow can be placed at the patient lap so he/she can bend forward and keep his/her chin towards his/her chest (angry cat position).

Procedure Steps

Position the patient as mentioned above
Identify the landmarks anatomically by palpating the midline vertebral columns of L4 at the level of the posterior superior iliac crests. (Adult injection site – any interspinous space from L2-S1 as the spinal cord terminates at L1 level. However, pediatrics injection site should be only from L3-L4/L4-L5 interspinous space as the conus medularis ends at the level of L1-L3).
Use a skin-marking pen to approximate the entry site.
Gown up and maintain universal precautions (sterile gloves, surgical facemask, and head cap).
Apply the antiseptic solution in a circular motion starting from the entry site to the periphery.
Apply the sterile drape.
Create a skin wheal of 1% Lidocaine; make sure it is no more than 1mL to avoid losing the landmark. Then inject into the deeper tissues.
Advanced the needle at the midline with your dominant hand holding the hub and your non-dominant hand supporting the needle by placing the thumb/index finger on the shaft of the needle for balance, parallel to the bed. The angle should be facing upward, aiming at the umbilicus.
Characteristic “pop” is occasionally felt when the needle passes the dura. If there is no sound, draw the stylet periodically checking for the CSF after approximately 4-5 cm.
Once CSF starts to drain, attach the manometer to measure the pressure. Then, start collecting the fluid from tube number 1 to 4 in sequence pattern. No more than 1mL in 1-3 tubes, then 3-4mL in tube 4.
Replace the stylet before removing the needle; then, remove both of them together.
Cover the injection site with the adhesive plaster.

Hints and Pitfalls

Like any other procedure, preparation is a must. Position the patient, palpate his back, get to know his anatomy, then mark it with a marking pen.
Your patient is elderly, and you are hitting a bone only after insertion of 25% of your needle. In most patients, the needle should be inserted 50-75% of its length prior to obtaining CSF flow.
- You may be hitting calcified supraspinal ligament.
- Try to enter from the lateral aspect to avoid the calcified ligament.
The patient can get very anxious and alarmed.
- Talk to the patient; he can’t see what you are doing. Tell him what step you are going to do.
- Ask someone to help you hold the patient and maintain his position during the procedure.
- If still anxious, give him/her some anxiolytic or even sedation if necessary.
Injecting lidocaine can sometimes obscure your landmark.
- Try not to inject more than 1mL to make a wheal; then, inject the remaining in the deeper tissues.
The traditional teaching “feel the first pop then the second pop, CSF will flow.”
- Never depend on the pop. Most of the time a series of pops are felt instead, as several spinal ligaments are encountered prior to entering the space.
In obese patients,
- Use the full length of the needle to 3.5-inch, or use the 6-inch “harpoon” needle.
- Try to do it in a sitting position.
CSF is red or tinged red
- The needle is too deep and hits a venous plexus leading to a traumatic tap. On the other hand, it’s subarachnoid hemorrhage or meningitis.
- Signs of a traumatic tap
  - The absence of xanthochromia (shows up within 12 hours and persists 2-4 weeks). If present at the time of the taping then its highly suggest SAH.
  - RBC count 400-500 RBCs or less suggestive of the traumatic tap. Must become zero at one of the last tubes.
  - RBC counts taper down from tube 1 to tube 4. This is not fully reliable unless it is completely clear by the 4th tube, but classically, the RBC count decreases by 30%.
  - Examining the 4th tube as a separate entity can also help rule out SAH
    - <100 RBC: almost certainly traumatic
    - <500 RBC: probably traumatic
    - >10K RBC: likely SAH
Is it bacterial or viral?
- There are couple measures helping us to identify the cause. These are
  - Opening pressure (cmH2O)
  - WBC count (per mm3)
  - Neutrophils (%)
  - Glucose (mg/dL)
  - Protein (mg/dL)
  - Culture or gram stain
- Normal values include 5-20 cmH2O opening pressure, equal to or less than 5 WBC per mm3, no neutrophils, 50-80 mg/dL glucose and 20-45 mg/dL protein.
- The bacterial CSF sample shows elevated opening pressure >500 WBC per mm3, >80% PMNL, low glucose (<40 mg/dL), and increased protein (>50 mg/dL). In addition, culture or gram stain indicates bacteria. The viral sample, however, shows normal or slightly elevated opening pressure, 100 – 500 WBC, neutrophils less than 50% and lymphocytic predominance, normal glucose, protein is normal or slightly elevated, and culture or gram stain indicates the virus.

Post-procedure Care and Recommendations

The patient may lie flat; however, there is controversial evidence that it may reduce headache incident.
Vital sign should be recorded depending on the hospital guidelines.
Neurological examination at least every 4 hours within the first 24 hours.
Encourage fluid intakes up to 3L/24hrs (tea and caffeine may help).
Monitor the puncture site for any bleeding, CSF leakage or infection.
Ensure the patient void after 8 hours post procedure.
Administer analgesia accordingly.
Do not forget the documentation.

Complications

Post–LP headache is the most common complication. It results from the reduction of CSF below the cisterna magna. It can’t be prognostic or prevented. Starts within the first 48hrs. A mild headache, self-limited, only needs conservative therapy (e.g. bed rest, oral analgesia, in some cases caffeine drinks can help). A refractory headache, an epidural blood patch is recommended. Using non-cutting, smaller diameter needle can decrease the occurance. 20-22 gauge atraumatic needles are the best choice.

Other complications are;