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

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.

Prospective randomized clinical study.

Fifteen adult cats (6 male, 9 female, 3.1 ± 0.4 kg [ x¯ ± SD]).

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.

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.

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.