Comparing respiratory variables with circle, Bain and T-piece breathing systems in 5-10 kg dogs: a randomized...

To compare respiratory rate (f_R), end-expired carbon dioxide (Pe'CO₂) and tidal (Vt) and minute (V˙ E) volume through a Bain or circle breathing system against a T-piece control.

Randomized, non-blinded, crossover clinical trial.

A group of 30 client-owned dogs (5-10 kg) undergoing general anaesthesia for elective procedures.

Equal groups of dogs were randomly allocated to the test breathing systems (either circle or Bain) then the order of breathing systems was randomized (test or control first). All dogs received a standard anaesthetic protocol. Following induction, 10 minutes was allowed to achieve a stable anaesthetic plane. Measurements were obtained over a 5 minute window for each system. After each breathing system change, 5 minutes was allowed for the dog to adjust. Measurements were compared using a paired Student's t-test or Wilcoxon rank test.

The circle Pe'CO₂ (6.04 ± 0.64 kPa), Vt (12.1 ± 3.9 mL kg^-1) and V˙e [116.7 (97.5-166.0) mL kg^-1 minute^-1] were significantly higher (p = ≤ 0.001, 0.035 and 0.002, respectively) than the T-piece Pe'CO₂ (5.31 ± 0.78 kPa), Vt [10.6 (7.7-13.3) mL kg^-1] and V˙ E [107.8 (77.3-131.9) mL kg^-1 minute^-1]. The Bain Pe'CO₂ (5.22 ± 0.98 kPa) was significantly lower (p = 0.032) and the Vt (7.1 ± 2.7 mL kg^-1) significantly higher (p = 0.041) than the T-piece Pe'CO₂ (5.61 ± 0.90 kPa) and Vt [6.6 (4.8-7.0) mL kg^-1]. Between the Bain and T-piece there was no significant difference in V˙ E. f_R was similar in both systems compared with the control.

While differences were found between both test systems and the control, the clinical consequences appear minimal. Both circle and Bain, appear suitable for use in healthy 5-10 kg dogs as overall ventilatory function was adequate.