Influence of two different ventilation modes on the function of an anaesthetic conserving device in sevoflurane anaesthetized piglets

Abstract

ObjectiveTo investigate the influence of two ventilation modes on the performance of an anaesthetic conserving device (AnaConDa) in piglets. Study designProspective randomized experimental trial. AnimalsEight female piglets weighing 24.7 ± 2.2 kg. MethodsAnaesthesia 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. ResultsAlthough 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 < 0.001, p = 0.015 respectively). Conclusions and clinical relevanceThe observed differences in E′Sevo concentration and sevoflurane breakthrough were probably related to differences in V˙T. The observed high FiCO2 indicated an excessive dead space with the AnaConDa for these piglets.