Postoperative respiratory failure (PRF) is a dreaded complication that imposes a significant burden through unplanned admission to the ICU, post discharge disability and mortality. Despite widespread implementation of intraoperative lung-protective ventilation strategies over the past decade, results remain inconsistent. Interventions targeting individual parameters like tidal volume or positive end-expiratory pressure (PEEP) have shown equivocal results. The use of high PEEP and recruitment maneuvers raises safety concerns by possible negative hemodynamic effects. Recent studies suggest that individualizing ventilation strategies based on mechanical power-a composite parameter integrating tidal volume, plateau pressure, PEEP, and ventilator frequency-may better predict and help prevent PRF, independently of patients' baseline respiratory system compliance. These studies identified this parameter as interventional targets to reduce lung injury during mechanical ventilation. However, no multicenter randomized controlled trial has been performed in the field of ventilatory settings titration during invasive mechanical ventilation in operating room.
The investigators hypothesize that a ventilation strategy aimed at decreasing mechanical power will reduce the incidence of PRF and mortality in patients undergoing abdominal surgery, compared with a standard strategy using fixed tidal volume and PEEP
Adult (≥ 18 years)
Laparoscopic or non-laparoscopic abdominal surgery
With an expected duration of at least 2 hours
Patients already receiving mechanical ventilation > 12 hours before surgery;
Chronic respiratory disease requiring oxygen therapy or mechanical ventilation at home;
Undrained pneumothorax or subcutaneous emphysema;
Intracranial hypertension;
Parallel
Mechanical power-guided ventilatory strategy
Procedure/Surgery1. Tidal volume 7ml/kg PBW and RR titrated for EtCO2 between 40-50mmHg. See calculated Mechanical power:0,049\*tidal volume\*RR\*driving pressure. 2. Set PEEP 15cmH2O and perform recruitment maneuver at 30cmH2O for 20s. Decrease PEEP from 15 by steps of 2cmH2O until the lower level of PEEP minimizing mechanical power. Note mechanical power. Stop maneuver and/or decrease level of PEEP if decrease\>20% of cardiac output during the maneuver, when compared to baseline. 3. Repeat this step using 9 ml/kg PBW and choose the optimal tidal volume with lowest mechanical power. During the surgery, adjust RR to maintain EtCO2 between 40-50mmHg, with an inspiratory-to-expiratory time ratio of 1:2 to 1:1, an end-inspiratory pause of 30%, an FiO2 adjusted to maintain SpO2≥94%. Recruitment maneuvers will be performed after intubation, in case of ventilator disconnection, coelioscopy insufflation, change of position, at the end of surgery, or if mechanical power \>30%.
Standard fixed ventilatory settings
Procedure/SurgeryTidal volume 7 ml/kg predicted body weight, calculated according to a predefined formula: 50+0.91 x (centimeters of height - 152.4) for males and 45.5+0.91 x (centimeters of height - 152.4) for females, fixed PEEP between 6 and 8 cmH20, recruitment maneuvers at the discretion of the physician. The respiratory rate will be adjusted to maintain end-tidal partial pressure of CO2 between 30 and 40 mmHg, a target reported to be used by approximately 90% of physicians according to a recent online survey administered to French anesthesiologists via the French Society of Anesthesia \& Intensive Care Medecine (SFAR), which will be published soon, with an inspiratory-to-expiratory time ratio of 1:2 to 1:1, an end-inspiratory pause of 30 %, and an FiO2 adjusted to maintain SpO2 ≥ 94%. Mechanical power will not be measured during the surgery to avoid any modification of the ventilatory setting by the physician in charge.
Composite of postoperative respiratory failure
Defined as failure to wean from the ventilator within the first 12 hours after surgery
Composite of postoperative respiratory failure
Defined as the need for unplanned reintubation following the end of surgery, once extubated
Composite of postoperative respiratory failure
Defined as the need for therapeutic non-invasive ventilation following the end of surgery, once extubated
All-cause mortality
Defined as death from any cause occurring within 30 days following surgery. The time to death will be measured from the date of surgery to the date of death. Patients discharged from hospital alive before Day 30 or still alive at Day 30 will be considered censored at that time.
Severity of postoperative pulmonary complications following surgery
The severity of pulmonary complications after surgery will be scored on a grade scale ranging from 0 to 4, with grade 0 representing the absence of any pulmonary complication and grades 1 through 4 representing successively the worse forms of pulmonary complications
Renal dysfunction following surgery
Postoperative renal dysfunction will be assessed using the Kidney Disease: Improving Global Outcomes (KDIGO) Acute Kidney Injury Classification, based on serum creatinine levels and urine output criteria. The KDIGO classification ranges from Stage 0 to Stage 3, where higher stages indicate more severe renal dysfunction (Stage 0 = no acute kidney injury; Stage 3 = most severe acute kidney injury). Renal dysfunction will be defined as KDIGO Stage 1 or higher.
Sepsis and septic shock following surgery
Will be evaluated after surgery, according to the last recommendations on sepsis and septic shock
Sepsis-related Organ Failure Assessment (SOFA)
The SOFA score will be collected at randomization, at Day 1, at Day 7 to evaluate the extent of organ dysfunction. The score includes six organ systems: respiratory, cardiovascular, hepatic, coagulation, renal, and neurological function. Each system is graded from 0 (normal function) to 4 (severe dysfunction) based on objective clinical or laboratory parameters. The Glasgow Coma Score will be excluded from the calculation
Postoperative hypoxemia
Defined as a PaO₂/FiO₂ ratio ≤ 300 mmHg measured by arterial blood gas analysis performed within 1 hour after extubation, indicating early hypoxemic respiratory failure following surgery
Postoperative pneumonia
Defined as a new or progressive pulmonary infiltrate on chest imaging combined with at least one clinical sign (fever, abnormal white blood cell count, purulent secretions, or positive respiratory culture), occurring after surgery, according the European Perioperative Clinical Outcome (EPCO) criteria
Acute Respiratory Distress Syndrome (ARDS)
Defined as acute hypoxemic respiratory failure with bilateral pulmonary opacities not fully explained by cardiac failure or fluid overload, and a PaO₂/FiO₂ ratio ≤ 300 mmHg with PEEP ≥ 5 cmH₂O, under invasive or non-invasive ventilation
Total intraoperative intravenous fluid volume
The total volume of crystalloids and colloids (millilitres) during surgery will be recorded
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