2.1. Patients

The study was approved by the regional ethics committee 02/07/2014 (REC South-East, 2013/1605) and registered in http://www.clinicaltrials.gov 02/23/2014 ({"type":"clinical-trial","attrs":{"text":"NCT02070861","term_id":"NCT02070861"}}NCT02070861), prior to patient enrolment. Forty adult patients scheduled for open coronary artery bypass surgery or aortic valve replacements were included from April 2014 to June 2015. Written informed consent was obtained prior to surgery. Patients with atrial fibrillation or ejection fraction <40% and patients in whom oesophageal Doppler placement was contraindicated were not included. The study was conducted in the cardiothoracic recovery unit of a university hospital 1-2 h after surgery. Patients were sedated with propofol 2-3 mg/kg/h according to departmental practice. They were haemodynamically stable prior to interventions, as evaluated by the attending cardiothoracic anaesthesiologist. Patients were ventilated in pressure-regulated volume control mode, tidal volumes 6–8 mL/kg predicted body weight, positive end-expiratory pressure 5–8 cmH₂O, risetime 0.20 s, FiO₂ as required for SpO₂ >94%, and frequency 9–13 breaths/min, adjusted to obtain an EtCO₂ between 32 and 38 mmHg before interventions (Evita Infinity C 500, Drägerwerk AG&Co, Lübeck, Germany). Ventilation and medication were kept constant during interventions (Table 1).

Patient characteristics.

Data are mean ± SD unless otherwise stated. PIP = peak inspiratory pressure; PEEP = positive end-expiratory pressure; CABG = coronary artery bypass grafting; AVR = aortic valve replacement; COPD = chronic obstructive pulmonary disease.