Isoflurane potency in the dog and cat
Steffey, E.P.; Howland, D.
American Journal of Veterinary Research 38(11): 1833-1836
1977
ISSN/ISBN: 0002-9645 PMID: 931167 Document Number: 114210
Cardiopulmonary effects of isoflurane, a new inhalation anaesthetic, were investigated in healthy unpremedicated dogs and cats under conditions of spontaneous and controlled (dogs only) ventilation. Measurements were made at minimum alveolar concentration (MAC) multiples of 1, 1.5, 2 and 3 in dogs and 1, 1.5, 2 and 2.4 in cats. The isoflurane MAC was 1.28 plus or minus 0.06% for dogs and 1.63 plus or minus 0.02% for cats. As anaesthetic dose increased, mean arterial pressure consistently and significantly decreased. Cardiac output, measured only in dogs, was sustained only during light or moderate levels (1 to 2 MAC) of anaesthesia because the heart rate significantly increased. Stroke volume, total peripheral resistance, and left ventricular work tended to decrease as anaesthesia deepened. There was little difference in cardiovascular measurements in dogs between spontaneous and controlled ventilation at equal MAC multiples. That isoflurane is a profound respiratory depressant in dogs and cats was supported by findings of a dose-dependent increase in arterial CO2 tension. In addition, the alveolar isoflurane concentration required to produce at least 60 seconds of apnea divided by MAC (i.e., the anaesthetic index) averaged 2.5 for dogs and 2.4 for cats. The anaesthetic index determined for isoflurane in dogs equals or is less than the index reported for other inhaled anaesthetics in this species.