Vaporizer in circle for delivery of isoflurane to dogs

An in-circuit vaporizer for delivery of isoflurane was evaluated. The isoflurane concentration within an isolated circle breathing circuit was determined for 1 hour in 6 in-the-circuit vaporizers with the wicks removed. A mechanical ventilator and artificial lung were connected to the circuit. Isoflurane concentration increased as vaporizer setting increased, and delivered concentration (%) at 60 minutes (mean +/- SEM) ranged from 0.46 +/- 0.10 at tap setting 1 to 3.67 +/- 0.30 at setting 5. Temperature of the isoflurane did not change. Cardiovascular and respiratory function were maintained within a clinically acceptable range in 6 dogs anesthetized with thiamylal and maintained with 1.87% end-tidal isoflurane delivered from the in-circuit vaporizer during spontaneous ventilation, controlled ventilation, and closed-circuit anesthesia. The range of vaporizer tap settings (mean +/- SEM) was lower during closed-system anesthesia (2.5 +/- 0.1 to 3.5 +/- 0.6) and during controlled ventilation (2.6 +/- 0.2 to 3.3 +/- 0.2) than during semi-closed system anesthesia (5.4 +/- 0.3 to 6.8 +/- 0.4). The in-circuit vaporizer was used to deliver isoflurane to 36 dogs anesthetized for a variety of surgical and medical procedures. Ventilation was spontaneous, assisted, and in 1 instance, controlled. Cardiovascular function, respiratory function, and recovery times were within clinically acceptable ranges. The initial vaporizer tap setting (mean +/- SEM) was 8.2 +/- 0.4, and this corresponded to an end-tidal isoflurane concentration of 3.5 +/- 0.6. The range of vaporizer settings during the maintenance phase (mean +/- SEM) was 2.8 +/- 0.5 to 4.6 +/- 1.9.(ABSTRACT TRUNCATED AT 250 WORDS)