Overview
Definition:
Lumbar puncture (LP) is a diagnostic procedure involving the insertion of a needle into the subarachnoid space in the lumbar region of the spinal column to obtain cerebrospinal fluid (CSF)
In infants, it is a crucial tool for diagnosing central nervous system infections, inflammatory conditions, and other neurological disorders.
Epidemiology:
Neonates and infants are particularly vulnerable to CNS infections like meningitis and sepsis due to immature immune systems
LP is frequently performed in these age groups when clinical suspicion of CNS involvement arises, especially in cases of unexplained fever, lethargy, or seizures.
Clinical Significance:
Accurate positioning is vital for success and minimizing complications in infants
Timely and correct interpretation of CSF findings can lead to early diagnosis and initiation of appropriate treatment, significantly impacting patient outcomes and preventing long-term sequelae
This procedure is a cornerstone of pediatric neurology and infectious disease management.
Positioning
Infant Positioning:
The infant should be positioned in a lateral decubitus position, with the spine flexed maximally
This can be achieved by an assistant holding the infant with their knees tucked towards their abdomen and chin tucked towards their chest
Alternatively, the infant can be placed in a seated position on the parent's lap with appropriate flexion
Maintaining flexion is key to widening the interspinous spaces
Avoid excessive flexion which can obscure landmarks or cause airway compromise
In a neonate, the spine is more pliable and the intervertebral spaces are narrower, requiring careful attention to flexion.
Anatomical Landmarks:
Identify the iliac crests
a line drawn between them typically intersects the L4 vertebral body or L3-L4 interspace
The needle is usually inserted at the L3-L4 or L4-L5 interspace
In infants, the conus medullaris typically terminates at L3, so insertion below L3 is generally safer to avoid spinal cord injury
Palpate the spinous processes and the posterior superior iliac spines to guide needle placement
Ultrasound guidance can be beneficial in neonates and infants to identify anatomical landmarks and the subarachnoid space.
Needle Selection:
A 22-25 gauge, 1 to 1.5-inch spinal needle with a stylet is typically used for infants
The stylet prevents the needle from clogging with tissue
A non-traumatic (pencil-point) needle may reduce the risk of post-lumbar puncture headache
Ensure the needle is oriented bevel-up to align with the dural fibers.
Sterility And Asepsis:
Strict sterile technique is paramount
The skin at the insertion site should be cleaned with an antiseptic solution (e.g., chlorhexidine or povidone-iodine) and allowed to dry
Sterile gloves, mask, and gown should be worn by the operator
A sterile drape should be used to isolate the puncture site.
Procedure Technique
Insertion Technique:
After identifying landmarks and ensuring sterile technique, the needle is inserted perpendicular to the skin surface, directed cephalad and slightly anterior
The stylet is slowly withdrawn as the needle is advanced
Resistance will be felt as the needle passes through the ligamentum flavum into the subarachnoid space
Once CSF is encountered, the stylet is removed to allow CSF flow
If blood is encountered, withdraw the needle and reattempt in a different interspace.
Fluid Collection:
Collect CSF into at least three sterile tubes
Tube 1: for cell count and differential
Tube 2: for chemistry (glucose, protein) and microscopy
Tube 3: for microbiology (Gram stain, culture, antigen detection)
If viral studies are required, an additional tube may be needed
The volume of CSF collected should be minimized, typically 0.5-1 mL for neonates and infants.
Post Procedure Care:
After CSF collection, the needle is withdrawn, and gentle pressure is applied to the puncture site with a sterile gauze
A sterile dressing is applied
The infant should be observed for signs of complications like headache, vomiting, or neurological changes
Encourage oral fluids if the infant is tolerating them
routine bed rest is not typically required for infants unless other complications arise.
Csf Interpretation In Infants
Normal Values Pediatrics:
Normal CSF parameters in infants are slightly different from adults
Opening pressure (if measured, usually not routinely done in infants): <20 cm H2O
Cell count: <5 cells/µL (mostly lymphocytes)
Protein: <90 mg/dL (can be up to 110 mg/dL in neonates)
Glucose: >40 mg/dL or >2/3 of serum glucose
WBC differential: >70% lymphocytes
Red blood cells: 0.
Bacterial Meningitis:
Typical findings include: elevated opening pressure, high WBC count (>1000 cells/µL, predominantly neutrophils), elevated protein (>100 mg/dL, often >200 mg/dL), low glucose (<40 mg/dL or <2/3 serum glucose), positive Gram stain (in 60-90% of cases), positive culture (in 80-90% of cases).
Viral Meningitis:
Typical findings include: normal or slightly elevated opening pressure, mild to moderate pleocytosis (WBC count 10-1000 cells/µL, predominantly lymphocytes), normal or slightly elevated protein (<100 mg/dL), normal glucose
PCR for specific viruses is often diagnostic.
Other Pathologies:
Fungal meningitis: pleocytosis with lymphocytes/neutrophils, elevated protein, normal or low glucose, positive India ink or cryptococcal antigen
Tuberculous meningitis: often a lymphocytic pleocytosis, elevated protein, low glucose, positive acid-fast bacilli stain or culture (takes time)
Neonatal sepsis with CNS involvement: CSF findings can be variable, often mirroring sepsis with pleocytosis, elevated protein, and low glucose
Subarachnoid hemorrhage: elevated red blood cells, xanthochromia (yellow discoloration) of CSF after several hours
Traumatic tap: presence of red blood cells that decrease in serial tubes, and the supernatant becomes clear, not xanthochromic.
Complications
Common Complications:
Post-lumbar puncture headache (less common in infants than older children, may present as irritability or feeding refusal), bleeding (epidural or subdural hematoma, especially with coagulopathy), infection (meningitis if sterile technique is breached), pain, and transient neurological deficits.
Rare Complications:
Spinal cord injury (if needle inserted too high), nerve root damage, herniation (especially in infants with significantly raised intracranial pressure).
Prevention Strategies:
Meticulous sterile technique, correct anatomical landmark identification, appropriate needle size, adequate hydration of the infant, and avoiding LP in cases of severe coagulopathy without correction
Ultrasound guidance can enhance safety and success rates.
Key Points
Exam Focus:
Understanding appropriate positioning for infant LP is critical
Differentiating between bacterial and viral meningitis based on CSF parameters is a frequent exam question
Normal CSF values in neonates/infants are distinct from adults.
Clinical Pearls:
When in doubt about landmarks, use ultrasound
Always collect CSF in sterile tubes for appropriate laboratory analysis
Never delay antibiotic treatment for suspected bacterial meningitis while awaiting LP results
administer empirically if diagnosis is strongly suspected.
Common Mistakes:
Incorrect positioning leading to failed puncture or injury
Misinterpreting CSF values due to lack of awareness of age-specific normal ranges
Delaying empiric antibiotics in suspected bacterial meningitis
Collecting insufficient CSF volume for all necessary tests.