Minimum alveolar anesthetic concentration of volatile anesthetics in normal and cardiomyopathic hamsters

Blockade of 5-HT(2A) and/or 5-HT(2C) receptors modulates sevoflurane-induced immobility

PURPOSE

Blockade of 5-hydroxytryptamine (5-HT)(2A) receptors reportedly mediates or modulates the ability of isoflurane to produce immobility during noxious stimulation and would thereby influence MAC (the minimum alveolar concentration required to suppress movement in response to noxious stimulation in 50% of subjects). However, no data are yet available regarding the role of this receptor in the immobilizing action of sevoflurane. In this study, we examined how prior intraperitoneal administration of either the 5-HT(2A) receptor antagonist altanserin or the 5-HT(2C/2B) receptor antagonist SB 206553 might affect sevoflurane MAC in rats.

METHODS

Three groups of six male Wistar rats weighing 250-350 g each received one of the following drugs dissolved in dimethyl sulfoxide intraperitoneally 30 min before MAC testing: (1) altanserin 10 mg/kg; (2) SB 206553 10 mg/kg; (3) no drug (vehicle control). MAC was defined as the average of the concentrations that just prevented or just permitted movement in response to clamping the tail for 1 min.

RESULTS

The rank order of MAC values obtained after intraperitoneal drug pretreatment and sevoflurane exposure was altanserin < SB 206553 < vehicle control.

CONCLUSION

Considering the low levels of 5-HT(2B) receptors within the CNS, this result suggests that 5-HT(2A) and the 5-HT(2C) receptors are present within the neural circuitry influencing sevoflurane MAC. Blockade of 5-HT(2A) and/or 5-HT(2C) receptors may modulate the immobility produced by sevoflurane during noxious stimulation.

Minimum alveolar concentration of sevoflurane in spontaneously breathing llamas and alpacas

OBJECTIVE

To determine the minimum alveolar concentration (MAC) of sevoflurane in spontaneously breathing llamas and alpacas.

DESIGN

Prospective study.

ANIMALS

6 healthy adult llamas and 6 healthy adult alpacas.

PROCEDURE

Anesthesia was induced with sevoflurane delivered with oxygen through a mask. An endotracheal tube was inserted, and a port for continuous measurement of end-tidal and inspired sevoflurane concentrations was placed between the endotracheal tube and the breathing circuit. After equilibration at an end-tidal-to-inspired sevoflurane concentration ratio > 0.90 for 15 minutes, a 50-Hz, 80-mA electrical stimulus was applied to the antebrachium until a response was obtained (ie, gross purposeful movement) or for up to 1 minute. The vaporizer setting was increased or decreased to effect a 10 to 20% change in end-tidal sevoflurane concentration, and equilibration and stimulus were repeated. The MAC was defined as the mean of the lowest end-tidal sevoflurane concentration that prevented a positive response and the highest concentration that allowed a positive response.

RESULTS

Mean +/- SD MAC of sevoflurane was 2.29 +/- 0.14% in llamas and 2.33 +/- 0.09% in alpacas.

CONCLUSIONS AND CLINICAL RELEVANCE

The MAC of sevoflurane in llamas and alpacas was similar to that reported for other species.