PT34 How to Perform a CSF Tap in the Cat Laurie Pearce DVM DACVIM Neurology Colorado State University Veterinary Medical Center Fort Collins CO USA OBJECTIVES OF THE PRESENTATION To by pyd12122


How to Perform a CSF Tap in the Cat
Laurie Pearce, DVM,DACVIM (Neurology)
Colorado State University Veterinary Medical Center
Fort Collins, CO, USA

     To provide reference information on patient selection and contraindications
     To describe equipment necessary to perform a spinal tap
     To describe the technique for a cisternal spinal tap
     To describe the technique for a lumbar spinal tap
     To provide reference information on sample analysis

     Procedure commonly included in the workup of any patient with neurologic dysfunction
     Abnormal result supports a disease process, rarely confirms a diagnosis
     Most helpful in the support of CNS inflammatory disease
     Patient instability may increase anesthetic risk to unacceptable level
     Suspect increased intracranial pressure
     Significant risk in a patient with a space occupying intracranial lesion
     Risk of iatrogenic injury due to lack of experience with procedure
     Practice, practice, practice on cadavers
     Increased risk morbidity / mortality with CSF collection in the cat compared to the dog
     Spinal needle(s) with stylet: 22 gauge 1 1/2 inch; Clear plastic hub
     For a cisternal tap, consider a 22 gauge butterfly with distal cap removed
     Clippers, serum tubes (2–3), sterile gloves; ( I usually don’t use a sterile drape)
CSF Collection
Patient Preparation—Mandatory procedures
General anesthesia, intubation, sterile preparation of procedure site
Cisterna Magna
     Easiest and most reliable site
     Correct patient positioning is necessary for a successful tap
                 o Right lateral recumbency (right handed clinician)
                 o Bring the body to the edge of table with the head flexed at a right angle
                 o To obtain correct head placement:
                                A line from the tip of the nose to the occipital protuberance: Parallel to table
                                A straight line from top of one ear to the other: Perpendicular to table
     Collector: Rest wrists against table for stability and minimize fatigue
     Approach: Find the middle of the occipital protuberance at the caudal aspect of the skull
     Point of needle placement:
                 o Locate a point on the midline, 1/2 way between occipital protuberance & wings of
                      atlas, or
                 o Follow the caudal aspect of the occipital protuberance to its base
                 o Press down firmly on the midline and follow it caudally to the lowest point
                      between occipital protuberance and C1 (few millimeters)
     Procedure: Insert the needle thru the skin perpendicular to midline with bevel facing forward.
     Expect major resistance thru skin
                  o Slowly advance the needle, stopping after every 1–2 mm of advancement to
                      remove stylet and check for CSF flow
                  o May or may NOT feel a slight “pop” as you pass thru dura mater into dorsal
                      subarachnoid space
                  o If contact bone, slightly withdraw the needle about 1/3 its length, redirect bevel
                      caudally about 30 degrees and try again
                  o Repeat until positive fluid flow
     Collect fluid drops into serum tube (about 1 ml)
                  o If whole blood present, withdraw needle, discard and try again
                  o If blood tinged CSF is present, collect a sample in tube #1
                               Be patient as CSF may clear, then collect into tube #2
Lumbar Subarachnoid Space
               o Technically more difficult than a cisternal tap
               o Can be challenging in the dog; Much easier in cats
               o RBC contamination is common; Expect slow flow and small sample
   Procedure site: L7–S1 > L6–L7
               o Use a 1 1/2 inch 22 gauge needle here
               o I don’t drape because I may see a slight tail twitch
   Place patient in ventral recumbency with coxofemoral joints flexed
               o Locate the dorsal spine of L7 between the wings of ilium
               o Needle is inserted thru the skin (bevel forward) at slight forward angle into the L7–
                    S1 space
               o Advance toward the spinal canal seeking depression in the dura
               o If encounter bone, move bevel cranially or caudally and try again until pass into the
                    dorsal subarachnoid space
               o Continue until bevel contacts the floor of the vertebral canal
               o Retract the needle slightly to enter the ventral subarachnoid space
               o Withdraw the stylet and patiently watch for fluid flow
                             Hold off jugular veins
   May need to carefully aspirate fluid with a syringe:
               o Important to keep needle still; Excess motion => cord injury
Sample Analysis
    Analyze within 1 hour if possible (WBC evaluation is time dependent )
    CSF pressure: Nonspecific findings; Commonly omitted
    Physical appearance: Clear and colorless; Turbidity requires > 500 WBC cells / ul
                 o WBC count (total and differential): Most important part of CSF evaluation
                 o Confirms the presence of an infectious and / or an inflammatory process
    Protein content: Albumin + small amount immunoglobulin
    Culture and sensitivity: Often disappointing
    Three drops: 1 hemocytometer, 1 slide, 1 protein spot on urine dipstick
Normal Feline CSF Findings
      .         Cisternal                  Lumbar

WBCs / ul       <5           1–8 Lymphocytes & monocytes only
RBCs / ul       Minimal      Minimal
Protein mg/dl   < 25        < 45

     CSF analysis is a vital diagnostic tool in the evaluation of many patients with neurologic
     Spinal taps can and should be done in general practice but it requires a commitment to learning the
     procedure thru practice on cadavers
     A cisternal tap is considered easier, has a faster flow and provides a larger CSF volume with less
     contamination compared to lumbar puncture
     Arrangements should be made ahead of time for optimal sample analysis (local hospital)

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