An abstract from this study was previously published in Veterinary Anaesthesia and Analgesia (2001) 28, 210–211.
The effects of ketamine on the minimum alveolar concentration of isoflurane in cats
Article first published online: 4 JAN 2007
Veterinary Anaesthesia and Analgesia
Volume 34, Issue 1, pages 31–39, January 2007
How to Cite
Pascoe, P. J., Ilkiw, J. E., Craig, C. and Kollias-Baker, C. (2007), The effects of ketamine on the minimum alveolar concentration of isoflurane in cats. Veterinary Anaesthesia and Analgesia, 34: 31–39. doi: 10.1111/j.1467-2995.2006.00297.x
- Issue published online: 4 JAN 2007
- Article first published online: 4 JAN 2007
- Received 20 June 2005; accepted 1 December 2005.
- ketamine plasma concentrations;
- minimum alveolar concentration
Objectives To determine the minimum alveolar concentration (MAC) of isoflurane during the infusion of ketamine.
Study design Prospective, experimental trial.
Animals Twelve adult spayed female cats weighing 5.1 ± 0.9 kg
Methods Six cats were anesthetized with isoflurane in oxygen, intubated and attached to a circle-breathing system with mechanical ventilation. Catheters were placed in a peripheral vein for the infusion of fluids and ketamine, and the jugular vein for blood sampling for the measurement of ketamine concentrations. An arterial catheter was placed to allow blood pressure measurement and sampling for the measurement of PaCO2, PaO2 and pH. PaCO2 was maintained between 29 and 41 mmHg (3.9–5.5 kPa) and body temperature was kept between 37.8 and 39.3 °C. Following instrumentation, the MAC of isoflurane was determined in triplicate using a tail clamp method. A loading dose (2 mg kg−1 over 5 minutes) and an infusion (23 μg kg−1 minute−1) of ketamine was started and MAC was redetermined starting 30 minutes later. Two further loading doses and infusions were used, 2 mg kg−1 and 6 mg kg−1 with 46 and 115 μg kg−1 minute−1, respectively and MAC was redetermined. Cardiopulmonary measurements were taken before application of the noxious stimulus. The second group of six cats was used for the measurement of steady state plasma ketamine concentrations at each of the three infusion rates used in the initial study and the appropriate MAC value determined from the first study.
Results The MAC decreased by 45 ± 17%, 63 ± 18%, and 75 ± 17% at the infusion rates of 23, 46, and 115 μg kg−1 minute−1. These infusion rates corresponded to ketamine plasma concentrations of 1.75 ± 0.21, 2.69 ± 0.40, and 5.36 ± 1.19 μg mL−1. Arterial blood pressure and heart rate increased significantly with ketamine. Recovery was protracted.
Conclusions and clinical relevance The MAC of isoflurane was significantly decreased by an infusion of ketamine and this was accompanied by an increase in heart rate and blood pressure. Because of the prolonged recovery in our cats, further work needs to be performed before using this in patients.