Postoperative respiratory failure (PRF) is a dreaded complication that imposes a significant burden through unplanned admission to the intensive care unit (ICU) and post discharge disability. Respiratory failure evident by tracheal intubations 1 month following nonemergent, noncardiac surgeries has been associated with a nine-fold increase in mortality. Efforts to reduce the rates of PRF have incorporated intraoperative ventilation strategies as a central element, with lung-protective ventilation following recommendations for the ICU setting being broadly implemented over the past decade. Interventions targeting individual parameters like tidal volume have shown equivocal results. To summarize, two randomized clinical trials showed lung-protective ventilation with low tidal volume (VT) in addition to high positive end-expiratory pressure (PEEP) and recruitment maneuver (RM) to prevent against postoperative pulmonary complications when compared with ventilation with high VT plus low PEEP without RM. Two other large, randomized trials found no benefit of high PEEP with RM compared with low PEEP without RM in this setting, suggesting that beneficial effects arise primarily from the use of low VT ventilation. Concerns have also been raised about possible negative hemodynamic effects of high PEEP and RMs in these studies. One size does not fit all. Individualized strategies are needed, such as ones using driving pressure (plateau pressure - PEEP), to perform PEEP titration. Using this calculated parameter, reduced incidence of postoperative pulmonary complications has been demonstrated in small randomized controlled trials, and not achieved in others. However, tidal volume and respiratory rate are also important parameters to limit ventilator induced injuries, and are not considered when assessing driving pressure. Mechanical power, a concept that in addition to tidal volume, plateau pressure and positive end-expiratory pressure (PEEP) also integrates the ventilatory frequency, has been recently associated with a higher risk of PRF. This formula is now implemented in the most recent operating room ventilators, and used in routine by some teams, with lack of evidence showing an efficacy of this strategy to set ventilatory settings. Although it has become clear that high mechanical power identifies patients at risk of PRF both in the operating room and ICU, there is an ongoing debate about whether they are linked to PRF, or whether these parameters merely represent an epiphenomenon in patients with impaired respiratory system mechanics and elevated risk at baseline.
Recently, several studies showed that high mechanical power was associated with PRF independent from 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 made the hypothesis that a strategy aimed at decreasing mechanical power (tidal volume, respiratory rate and PEEP individually titrated to minimize the mechanical power) will reduce PRF and mortality in patients undergoing abdominal surgery, when compared with that of a strategy of standard care (with fixed level of tidal volume and PEEP). The investigators expect decreased PRF and mortality rate in the group "mechanical power-guided ventilatory settings". The investigators also expect in this group reduced duration of postoperative mechanical ventilation, reduced incidence of postoperative organ dysfunction, and reduced duration of hospital stay.
