Objective To investigate the influence of two ventilation modes on the performance of an anaesthetic conserving device (AnaConDa) in piglets. Study design Prospective randomized experimental trial. Animals Eight female piglets weighing 24.7 +/- 2.2 kg. Methods Anaesthesia was maintained with sevoflurane (in 60% oxygen) delivered from the AnaConDa placed between endotracheal tube (ETT) and Y-piece. Anaesthetic depth was guided using standard clinical parameters. Ventilation mode was volume controlled (VC) during the first and pressure support (PS) during the second period of anaesthesia in four piglets (group 1); the order was reversed in group 2. Anaesthetic gases were sampled before (at the proximal end of the ETT) and after the AnaConDa (Y-piece). Data were analysed using a model I ANOVA, with treatment and group as fixed categorical effects. Using a paired t-test, partial pressures of carbon dioxide (PE'CO2) on both sides of the device were compared. Results Although the mean administration rate of sevoflurane was comparable in both groups (3.8 +/- 1.8 mL hour(-1)), E'Sevo was higher in group 1, more specifically during the first period (p = 0.035). Less sevoflurane escaped during VC (14.0 +/- 3.4%) compared with PS ventilation (17.2 +/- 5.7%) (p = 0.001). PE'CO2 was lower at the Y-piece (6.4 +/- 0.8 kPa, 48 +/- 6 mmHg) compared with the ETT (9.3 +/- 1.4 kPa, 70 +/- 11 mmHg) in both groups and ventilation modes. On average, inspiratory CO2 tension was 2.0 +/- 1.0 kPa (15 +/- 8 mmHg). Respiration rate was comparable in all piglets while tidal volume (V-T) and peak inspiratory pressure were lower during VC compared with PS (p