Isoflurane potency in the dog and cat

Area of Science:

• Veterinary Anesthesiology
• Cardiopulmonary Physiology
• Comparative Medicine

Background:

• Isoflurane is a widely used inhalation anesthetic.
• Understanding its cardiopulmonary effects in dogs and cats is crucial for safe anesthetic practice.

Purpose of the Study:

• To investigate the cardiopulmonary effects of isoflurane in healthy dogs and cats.
• To compare effects under spontaneous and controlled ventilation in dogs.
• To determine the anesthetic index of isoflurane in these species.

Main Methods:

• Healthy, unpremedicated dogs and cats were administered isoflurane at increasing multiples of the minimal alveolar concentration (MAC).
• Cardiopulmonary parameters including mean arterial pressure, cardiac output, heart rate, stroke volume, and PaCO2 were measured.
• Ventilation was spontaneous or controlled in dogs.

Main Results:

• Isoflurane caused a dose-dependent decrease in mean arterial pressure and an increase in PaCO2 in both species.
• Cardiac output was maintained at lighter anesthetic levels (1.0-2.0 MAC) in dogs due to increased heart rate.
• Stroke volume, total peripheral resistance, and left ventricular work decreased as anesthesia deepened.

Conclusions:

• Isoflurane is a potent respiratory depressant in dogs and cats.
• Cardiovascular effects include hypotension and reduced cardiac performance at deeper anesthetic levels.
• The determined anesthetic index suggests isoflurane may have a narrower safety margin compared to other inhaled anesthetics in dogs.