Flow-controlled versus pressure-controlled ventilation in cardiac surgery with cardiopulmonary bypass - A single-center, prospective, randomized, controlled trial

Study objective: Multifactorial comparison of flow-controlled ventilation (FCV) to standard of pressure-controlled ventilation (PCV) in terms of oxygenation in cardiac surgery patients after chest closure.

Design: Prospective, non-blinded, randomized, controlled trial.

Setting: Operating theatre at an university hospital, Austria.

Patients: Patients scheduled for elective, open, on-pump, cardiac surgery.

Interventions: Participants were randomized to either individualized FCV (compliance guided end-expiratory and peak pressure setting) or control of PCV (compliance guided end-expiratory pressure setting and tidal volume of 6-8 ml/kg) for the duration of surgery.

Measurements: The primary outcome measure was oxygenation (PaO₂/FiO₂) 15 min after intraoperative chest closure. Secondary endpoints included CO₂-removal assessed as required minute volume to achieve normocapnia and lung tissue aeration assessed by Hounsfield unit distribution in postoperative computed tomography scans.

Main results: Between April 2020 and April 2021 56 patients were enrolled and 50 included in the primary analysis (mean age 70 years, 38 (76%) men). Oxygenation, assessed by PaO₂/FiO₂, was significantly higher in the FCV group (n = 24) compared to the control group (PCV, n = 26) (356 vs. 309, median difference (MD) 46 (95% CI 3 to 90) mmHg; p = 0.038). Additionally, the minute volume required to obtain normocapnia was significantly lower in the FCV group (4.0 vs. 6.1, MD -2.0 (95% CI -2.5 to -1.5) l/min; p < 0.001) and correlated with a significantly lower exposure to mechanical power (5.1 vs. 9.8, MD -5.1 (95% CI -6.2 to -4.0) J/min; p < 0.001). Evaluation of lung tissue aeration revealed a significantly reduced amount of non-aerated lung tissue in FCV compared to PCV (5 vs. 7, MD -3 (95% CI -4 to -1) %; p < 0.001).

Conclusions: In patients undergoing on-pump, cardiac surgery individualized FCV significantly improved oxygenation and lung tissue aeration compared to PCV. In addition, carbon dioxide removal was accomplished at a lower minute volume leading to reduced applied mechanical power.