CEREBROSPINAL-FLUID ACID-BASE STATUS DURING NORMOCAPNIA AND ACUTE HYPERCAPNIA IN EQUINE NEONATES

Objective-To determine normal acid-base status of the CSF and to compa re it with changes during acute hypercapnia in equine neonates. Animal s-10 clinically normal foals between 1 and 12 days old. Procedure-CSF and arterial and venous blood samples were collected every 15 minutes during 45 minutes of normocapnia and 90 minutes of hypercapnia in isof lurane-anesthetized foals. CSF samples were collected via a subarachno id catheter placed in the atlanto-occipital space. Results-Comparison of blood and CSF gases during normocapnia indicated that CSF was signi ficantly more acidic than blood. The lower pH was attributable to high er CO2 and lower bicarbonate concentrations than those in blood. Durin g hypercapnia, CSF CO2 increased and pH decreased parallel to changes in blood, but changes were not as great as similar changes in venous b lood, indicating that some degree of buffering occurs in the CSF of fo als. Conclusions-Normal CSF acid-base status in equine neonates is sim ilar to that in other domestic species. The blood-brain and blood-CSF interfaces in neonates allow rapid diffusion of CO2, but allow only sl ow diffusion of bicarbonate. Equine neonates are capable of buffering respiratory-induced acid-base changes in the CSF, but the buffering ca pacity is less than that of the vascular compartment. Clinical Relevan ce-Neonatal foals may develop severe respiratory compromise, resulting in hypoxemia and hypercapnia. Because the ability of the CSF to buffe r acid-base changes in neonates is reduced, hypercapnia may contribute to the CNS abnormalities that often develop in sick neonates, Thus, n ormal blood gas values should be maintained in diseased equine neonate s.