Effects of small tidal volume and positive end-expiratory pressure on oxygenation in pressure-controlled ventilation-volume guaranteed mode during one-lung ventilation

BACKGROUND: The purpose of this study was to investigate whether tidal volume (TV) of 8 mL/kg without positive end-expiratory pressure (PEEP) and TV of 6 mL/kg with or without PEEP in pressure-controlled ventilation-volume guaranteed (PCV-VG) mode can maintain arterial oxygenation and decrease inspiratory airway pressure effectively during one-lung ventilation (OLV). METHODS: The study enrolled 27 patients undergoing thoracic surgery. All patients were ventilated with PCV-VG mode. During OLV, patients were initially ventilated with TV 8 mL/kg (group TV8) without PEEP. Ventilation was subsequently changed to TV 6 mL/kg with PEEP (5 cmH(2)O; group TV6+PEEP) or without (group TV6) in random sequence. Peak inspiratory pressure (P(peak)), mean airway pressure (P(mean)), and arterial blood gas analysis were measured 30 min after changing ventilator settings. Ventilation was then changed once more to add or eliminate PEEP (5 cmH(2)O), while maintaining TV 6 mL/kg. Thirty min after changing ventilator settings, the same parameters were measured once more. RESULTS: The P(peak) was significantly lower in group TV6 (19.3±3.3 cmH(2)O) than in group TV8 (21.8±3.1 cmH(2)O) and group TV6+PEEP (20.1±3.4 cmH(2)O). PaO(2) was significantly higher in group TV8 (242.5±111.4 mmHg) than in group TV6 (202.1±101.3 mmHg) (p=0.044). There was no significant difference in PaO(2) between group TV8 and group TV6+PEEP (226.8±121.1 mmHg). However, three patients in group TV6 were dropped from the study because PaO(2) was lower than 80 mmHg after ventilation. CONCLUSION: It is postulated that TV 8 mL/kg without PEEP or TV 6 mL/kg with 5 cmH(2)O PEEP in PCV-VG mode during OLV can safely maintain adequate oxygenation.