Determination of the minimum alveolar concentration of sevoflurane in Holstein steers

To determine the minimum alveolar concentration (MAC) of sevoflurane in Holstein steers using electric stimulation.

Prospective experimental study.

A total of 15 Holstein steers aged 7.3 ± 1.2 months and weighing 121 ± 25 kg.

Animals were anesthetized with sevoflurane at 8% in oxygen at 5 L minute^-1 via facemask and were intubated with an orotracheal tube of a compatible size. After 15 minutes of stabilization of the initial expired concentration of sevoflurane (Fe'Sevo) at 2.6%, electrical stimulation on the thoracic limb was initiated with a sequence of 2 × 10 ms followed by 2 × 3 second electrical currents of 50 V and 50 Hz, 5 seconds apart. Following each stimulus with a negative response, the Fe'Sevo was decreased by 0.2% and a 15 minute interval was awaited before the next stimulus. The procedure was repeated until the first Fe'Sevo value with a positive motor response was obtained. The Fe'Sevo was then increased by 0.1%, followed by a new stimulus, until a negative response was obtained. The value of MAC was calculated as the arithmetic mean between the lowest Fe'Sevo associated with a negative motor response and the highest Fe'Sevo associated with a positive response.

The mean MAC for the 15 steers was 2.0 ± 0.3%, which corresponds to 2.1 ± 0.3% at sea level.

Based on the proposed methodology, the MAC of sevoflurane for healthy Holstein steers is 2.1 ± 0.3% at sea level.

This Fe'Sevo value can be used to guide depth of anesthesia in steers weighing approximately 120 kg in clinical practice.