Influence of Low Tidal Volume Ventilation on Time to Extubation in Cardiac Surgical Patients

Abstract

Low tidal volumes are clearly beneficial for patients with established acute respiratory distress syndrome/acute lung injury (ARDS/ALI).1–3 However, the optimal mechanical ventilation of patients at risk of ARDS/ALI remains unclear. In theory, lung overdistention could contribute to lung injury among predisposed individuals, leading to prolongation of mechanical ventilation. Gajic et al.4 conducted a retrospective analysis of patients who did not have ARDS when mechanical ventilation was initiated. They observed that high tidal volume was an independent risk factor for ALI among patients with relatively normal gas exchange. The authors4 concluded that strong consideration should be given to limiting large tidal volume, not only among patients with established ALI, but also for at-risk patients. Subsequent retrospective analyses have confirmed these findings.5,6 However, other researchers7 have suggested that low tidal volume may be unnecessary in non-ALI cases and that it may lead unnecessarily to patient discomfort, increased work during breathing, high sedation requirements, autopositive end-expiratory pressure (PEEP; high respiratory rate), hypercapnia (low respiratory rate), and atelectasis. Thus, despite biologic plausibility and considerable retrospective data to support limiting tidal volume in all ventilated patients, equipoise remains regarding optimal tidal volume in non-ALI patients. Although various groups of surgical patients, but especially cardiac surgical patients, have been observed,8–20 these investigations have focused primarily on surrogate outcomes measures, leaving a lack of clarity regarding optimal perioperative ventilator strategy. Therefore, we performed a randomized controlled trial comparing ventilation with 6 versus 10 ml/kg tidal volume for patients undergoing elective cardiac surgery. We hypothesized that using a low tidal volume ventilator strategy would reduce ventilator-associated lung injury and that this improvement would reduce time to extubation.