Cerebrospinal Fluid Collection

The lumbosacral (LS) site provides a representative sample of CSF and can be done in the standing or recumbent foal. An atlantooccipital (AO) tap can also be done if the foal does not have increased intracranial pressure. Normal intracranial pressure in healthy neonatal foals is reported between 2-15 mmHg [1]. Certain anesthetics (ketamine) may also increase intracranial pressure. Definitive signs of increased intracranial pressure in the foal are not known.

I. Materials Required

1. A. LS: 3 inch 20-gauge spinal needle; AO: 20-gauge, 1.5-2 inch disposable.
2. B. Sterile prep materials, surgical gloves.
3. C. Diazepam or midazolam for sedation.
4. D. Lidocaine, 25-gauge needle and 3 cc syringe.
5. E. 6 cc syringe for aspiration.
6. F. Sterile Vacutainer® for collection.

II. Lumbosacral Technique

1. Standing foals restrained by tail or rump and chest; or down in lateral recumbency.
2. Sedation - may aid restraint.
3. Have the foal stand with equal weight on rear limbs.
4. Locate caudal edge of L-6, mid portion of tuber sacrale and spine of sacral vertebrae.
5. Palpate depression posterior to L-6 and just cranial to a line connecting the mid portion of the two tuber sacrale.
6. Prep area - Shave, scrub, alcohol, Betadine.
7. Local bleb of anesthesia in skin over site.
8. Maintain needle in vertical plane with assistance from "spotter".
9. Penetrate skin, fascia, interarcuate ligament, dura mater, arachnoid membrane.
10. Remove stylet and aspirate at various levels; if no fluid aspirated, replace stylet and advance needle until meet bone.
11. A "pop" with brisk contractive movement of the foal indicates penetration into subarachnoid space.
12. Remove stylet, if CSF is blood tinged, draw first 2-3 cc in syringe and discard if fluid becomes clearer and save next 5 cc.
13. Gently draw 5 cc for protein, cytology, Gram stain, culture, -compress jugular veins to increase CSF pressure and flow into syringe.
14. Replace stylet and withdraw needle.
15. If hit bone remove and re-direct.
16. Frank blood in needle indicates have deviated off midline into venous sinus - Remove, change needle and redirect.

III. Atlantooccipital Site Technique

1. Need dependable immobilization – Caution: if penetrate too deeply permanent spinal cord damage may result.
2. General anesthesia preferred immobilization. Others have used 2-5 mg Diazepam-Valium® IV in semi-comatose foals and control of foal's legs and head in lateral recumbency.
3. Head should be at right angle to the neck.
4. Landmarks are point of intersection of an imaginary line between cranial borders of the wings of the atlas and midline.
5. Prep the site by shaving and scrub.
6. A palpable depression at the site is usually noted.
7. Position and insert a 20-gauge 1.5 inch disposable needle directed at the mandible.
8. Slowly advance and check for fluid. A change in resistance at a depth of 1-1.5 inches occurs on entry into the subarachnoid space.
9. Fluid will drain from the hub of the needle in droplets.
10. If a steady stream of clear fluid under pressure is seen, remove needle immediately as brain herniation may occur causing permanent damage.
11. Penetrating too deeply may damage the spinal cord.
12. Normally collect 3-6 cc of CSF.

IV. Normal Equine Neonatal CSF [2-4]

1. Total protein - 145 mg/dl ± 50.

1. Biuret method.
2. Use your laboratory normal values due to different methods.

2. Albumin 81 mg/dl ± 13.
3. Globulin 64 mg/dl ± 15.
4. Color - Clear.
5. Creatine Kinase (CK) -15.2 ± 9.2 IU/liter.

1. Extreme variation may be seen.
2. Does not correlate with serum levels.

6. White blood cell total - < 20/ul.
7. Red blood cell total - Variable usually <200/ul.
8. Glucose 30-70mg/dl
9. Sodium: 140-150 mEq/l
10. Potassium: 2.5-3.5 mEq/l

V. Interpretation [5,6]

1. Elevated proteins (>70 mg/dl), WBC (>7-10/ul) and increased neutrophils suggest infection.
2. Gram stain for organism -intracellular indicates infection.
3. Increased protein, xanthochromia may indicate spinal hemorrhage or vasculitis.
4. Glucose lower than 80% of blood glucose may suggest infection - This has not been determined in foals.
5. Increased protein and increase in small and large mononuclear cells suggests viral infection.
6. CSF analysis within normal parameters does not rule out septic meningitis. However, a positive finding indicates significant involvement and a poor prognosis [7].

Decreased buffering capacity of the CSF in foals compared to adults can cause rapid acid-base disturbances in the brain [8].