A comparison of the 'Maxima' and the modified Ayre's T-piece breathing systems in spontaneously breathing cats.

ABSTRACT

OBJECTIVE: To compare the fresh gas flow requirements of the 'Maxima' and Jackson-Rees modified Ayre's T-piece (JRMATP) in spontaneously breathing anaesthetized in cats. STUDY DESIGN: Prospective randomized clinical study. ANIMALS OR SAMPLE POPULATION Fifteen adult cats (6 male, 9 female, 3.1 ± 0.4 kg [ x¯ ± SD]). MATERIALS & METHODS: After pre-anaesthetic medication with acepromazine and pethidine, anaesthesia was induced using thiopentone and the trachea was intubated with a cuffed endotracheal tube. This was attached to either a 'Maxima' or a JRMATP breathing system; allocation was randomized. Anaesthesia was maintained with halothane delivered in a 1 1 oxygen nitrous oxide mixture. Initial total fresh gas flow (FGF) was set at 600 mL kg-1 min-1. After 20 minutes, FGF was reduced in increments of 200 mL min-1 until rebreathing (inspired CO2 concentration >0.2%) occurred. At this point, FGF was increased to 600 mL kg-1 and the process was repeated with the other breathing system. The respiratory rate and airway pressure at the endotracheal tube connector were monitored throughout anaesthesia. RESULTS: The mean fresh gas flow that prevented rebreathing with the Maxima system (164 ± 39 mL kg-1) was significantly less (p < 0.0001) than that required in the modified T-piece (455 ± 0.77 mL kg-1). Respiratory rates and airway pressures at the endotracheal tube connector were not significantly affected by breathing system employed. CONCLUSIONS: In terms of the gas flow requirements that prevent rebreathing, the 'Maxima' breathing system is more efficient than the modified Ayre's T-piece in spontaneously breathing cats anaesthetised with halothane.