Effects of ventilation and isoflurane end-tidal concentration on intracranial and cerebral perfusion pressures in horses.
OBJECTIVE
To measure the effects of isoflurane end-tidal concentration and mode of ventilation (spontaneous vs controlled) on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) in horses.


METHODS
adult horses of various breeds.


METHODS
Anesthesia was induced and maintained with isoflurane in O2 in 6 healthy, unmedicated, adult horses. Using a subarachnoid strain gauge transducer, ICP was measured. Blood gas tensions and carotid artery pressures also were measured. Four isoflurane doses were studied, corresponding to the following multiples of the minimum alveolar concentration (MAC): 1.0 MAC, 1.2 MAC, 1.4 MAC, and 1.6 MAC. Data were collected during controlled ventilation and spontaneous ventilation at each dose.


RESULTS
increasing isoflurane end-tidal concentration induced significant dose-dependent decreases in mean arterial pressure (MAP) and CPP but no change in ICR Hypercapnic spontaneous ventilation caused significant increases in MAP and ICR compared with normocapnic controlled ventilation; no change in CPP was observed.


CONCLUSIONS
Hypercapnia likely increases cerebral blood flow (CBF) by maintaining CPP in the face of presumed cerebral vasodilation in healthy anesthetized horses. The effect of isoflurane dose on CBF however, remains unresolved because it depends on the opposing influences of a decrease in CCP and cerebral vasodilation.
Brosnan
Robert J
RJ
Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Steffey
Eugene P
EP
LeCouteur
Richard A
RA
Imai
Ayako
A
Farver
Thomas B
TB
Kortz
Gregg D
GD
D018685:Anesthetics, Inhalation / Q000493:pharmacokinetics / Q000494:pharmacology*; D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary; D001794:Blood Pressure / Q000187:drug effects; D001921:Brain / Q000098:blood supply*; D002560:Cerebrovascular Circulation / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006736:Horses / Q000378:metabolism / Q000502:physiology*; D007427:Intracranial Pressure / Q000187:drug effects*; D007530:Isoflurane / Q000493:pharmacokinetics / Q000494:pharmacology*; D008297:Male; D012123:Pulmonary Ventilation / Q000187:drug effects; D011897:Random Allocation; D014655:Vascular Resistance / Q000187:drug effects; D014691:Ventilation / Q000379:methods
D018685:Anesthetics, Inhalation; D007530:Isoflurane