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To determine normal acid-base status of the CSF and to compare it with changes during acute hypercapnia in equine neonates.


10 clinically normal foals between 1 and 12 days old.


CSF and arterial and venous blood samples were collected every 15 minutes during 45 minutes of normocapnia and 90 minutes of hypercapnia in isoflurane-anesthetized foals. CSF samples were collected via a subarachnoid catheter placed in the atlanto-occipital space.


Comparison of blood and CSF gases during normocapnia indicated that CSF was significantly more acidic than blood. The lower pH was attributable to higher CO2 and lower bicarbonate concentrations than those in blood. During hypercapnia, CSF CO2 increased and pH decreased parallel to changes in blood, but changes were not as great as similar changes in venous blood, indicating that some degree of buffering occurs in the CSF of foals.


Normal CSF acid-base status in equine neonates is similar to that in other domestic species. The blood-brain and blood-CSF interfaces in neonates allow rapid diffusion of CO2, but allow only slow diffusion of bicarbonate. Equine neonates are capable of buffering respiratory-induced acid-base changes in the CSF, but the buffering capacity is less than that of the vascular compartment.

Clinical Relevance

Neonatal foals may develop severe respiratory compromise, resulting in hypoxemia and hypercapnia. Because the ability of the CSF to buffer acid-base changes in neonates is reduced, hypercapnia may contribute to the CNS abnormalities that often develop in sick neonates. Thus, normal blood gas values should be maintained in diseased equine neonates. (Am J Vet Res 1996;57:1483-1487)

Free access
in American Journal of Veterinary Research


Blood ionized calcium (Ca2+) and pH; plasma lactate concentrations; and total protein, total calcium (CaT), albumin, and phosphorus concentrations in serum were determined in 40 healthy horses before (T1), at the finish line (T2), and 10 minutes after the finish (T3) of the cross-country phase of a 3-day-event competition. Mean (± sem) Ca2+ concentrations decreased from 6.22 ± 0.04 mg/dl at T1 to 5.04 ± 0.07 mg/dl at T2 (P ≤ 0.05). This decrease was accompanied by a nonsignificant increase in CaT between T1 and T2. The mean (± sem) percent ionization of calcium decreased significantly (P ≤ 0.05), from 50.9 ± 2.75% at T1 to 40.3 ± 3.58% at T2. Significant increases in mean albumin, total protein, phosphorus, and lactate concentrations and a significant decrease in mean pH were observed at T2 (P ≤ 0.05). At T3, mean Ca2+ and percent ionization had increased, but remained significantly less than resting values. Mean CaT was significantly decreased at T3, compared with values at T1 and T2. Correlation of mean Ca2+ concentration with all other measured variables at each time was evaluated; correlation coefficients between mean Ca2+ and all other variables were low (r 2 ≤ 0.38), indicating low biological significance.

Free access
in American Journal of Veterinary Research