BACKGROUND: The effect of flow-controlled ventilation (FCV) as compared with volume-controlled ventilation (VCV) on oxygenation and respiratory system mechanics in patients undergoing one-lung ventilation (OLV) is unknown.

OBJECTIVE: To test the hypothesis that FCV would improve oxygenation and respiratory system mechanics compared with VCV during OLV.

DESIGN: Two-centre, two-arm, randomised controlled clinical trial.

SETTING: University hospital and speciality hospital for pulmonary diseases in Germany.

PATIENTS: A total of 78 thoracic surgery patients undergoing OLV for more than 30 min.

INTERVENTIONS: Patients were randomly assigned to OLV with FCV (n = 39), or VCV (n = 39). In both groups, OLV was conducted with tidal volume of 5 ml kg-1, positive end-expiratory pressure of 5 cmH2O, respiratory rate to normocapnia, and inspiratory oxygen fraction of 1.0.

MAIN OUTCOME MEASURES: The primary outcome was the arterial partial pressure of oxygen (PaO2) 20 min after initiation of OLV. The secondary outcomes included respiratory system mechanics, the need for rescue due to hypoxaemia, and clinical outcome variables.

RESULTS: The partial pressure of arterial oxygen did not differ between FCV and VCV at 20 min after starting OLV (PaO2: 24.8 ± 14.8 kPa vs. 26.1 ± 15.9 kPa, mean difference -1.2 (95% confidence interval -8.2 to 5.7), P = 0.721), while mechanical power was lower during FCV compared with VCV. Other variables did not differ at any time thereafter, except for the compliance of the respiratory system at end of surgery. The need for rescue manoeuvres due to hypoxemia or hypercapnia during OLV did not differ between the groups. The incidence of postoperative pulmonary and extrapulmonary complications, as well as the number of hospital-free days at day 30 after surgery, did not differ between FCV and VCV.

CONCLUSIONS: Compared with VCV in thoracic surgery patients, FCV did not improve oxygenation or respiratory system mechanics during OLV, nor was it associated with improved outcomes.