10-11-2012, 11:00 AM
Lumbar Puncture
Lumbar Puncture.ppt (Size: 411 KB / Downloads: 148)
CSF Formation
140 ml spinal and cranial CSF
30 ml in the spinal cord
Production is approx. 0.35 ml/min
Net flow out of ventricles 50 – 100 ml/day
Reduces brain weight from 1400 to 50g.
Indications for Lumbar Puncture
Primary indication for emergent spinal tap is possibility of CNS infection
The second indication for an emergent spinal puncture is a suspected spontaneous subarachnoid hemorrhage.
Infectious Indications
Fever of unknown origin
Children 1mo to 3yrs: fever, irritability, and vomiting. Cannot comfort child
Over age 3yrs: nuchal rigidity, Kernig’s sign, and Brudzinski’s sign
Petechial rash in a febrile child
Partially treated children are less likely to be febrile or exhibit an altered mental status
Subarachnoid Hemorrhage
Diagnosis usually made by CT scan or by blood in CSF.
Initial presentation: CT 92-98% accurate
Later than 24 hr presentation: 76% accurate
20-60% of aneurismal subarachnoid hemorrhage will have “sentinel thunderclap” or “warning clap”
After initial leak, CT is usually negative
Contraindications for LP
Absolutely contraindicated in the presence of infection in the tissues near the puncture site.
Relatively contraindicated in presence of SOL or increased ICP
Caution advised when lateralizing signs or signs of uncal herniation.
Interpretation
Appearance
If CSF is not crystal clear, a pathologic condition of the CNS should be suspected
Compare fluid to water
Fluid may be clear with as many as 400 RBCs/mm3 and 200 WBCs/mm3
Cells
WBC counts over 5 cells/mm3 should be taken to indicate the presence of pathologic condition
Polymorphonuclear leukocytes are never seen in normal adults
Neutrophilic pleocytosis is commonly associated with bacterial infections or early stages of viral infections, tuberculosis, meningitis, hematogenous meningitis, and chemical meningitis due to foreign bodies.
Protein
Increase in CSF total protein levels are a nonspecific abnormality associated with many disease states.
Levels > 500mg/dl are uncommon and are seen mainly in meningitis, in subarachnoid bleeding, and with spinal tumors.
CSF Analysis with Infections
Bacterial Infections
The Gram stain is of great importance, because this often dictates the initial choice of antibiotic.
Gram-negative intracellular or extracellular diplococci are indicative of Neisseria meningitidis
Small Gram-negative bacilli may include Haemophilus influenza, especially in children.
Gram-positive cocci indicates Streptococcus pneumoniae, other Streptococcus species, or Staphylococcus.
20% of Gram stains may be falsely negative.
While the culture is pending, one may suspect a bacterial infection in the presence of an elevated opening pressure and a marked pleocytosis ranging between 500 and 20,000 WBCs/mm3.
The differential count is usually chiefly neutrophils.
A count above 1000 cells/mm3 seldom occurs in viral infections.