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 compare it with changes during acute hypercapnia in equine neonates.


METHODS
10 clinically normal foals between 1 and 12 days old.


METHODS
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.


RESULTS
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 a great as similar changes in venous blood, indicating that some degree of buffering occurs in the CSF of foals.


CONCLUSIONS
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.


CONCLUSIONS
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.
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville 37901-1071, USA.
D R
DR
Geiser
F M
FM
Andrews
B W
BW
Rohrbach
M K
MK
Provenza
D000136:Acid-Base Equilibrium; D000818:Animals; D000831:Animals, Newborn; D001639:Bicarbonates / Q000097:blood / Q000134:cerebrospinal fluid; D002245:Carbon Dioxide / Q000097:blood* / Q000134:cerebrospinal fluid*; D005260:Female; D006736:Horses; D006863:Hydrogen-Ion Concentration; D008297:Male; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D012016:Reference Values; D013997:Time Factors
D001639:Bicarbonates; D002245:Carbon Dioxide; D010100:Oxygen