To the Editor:
I read with interest Park et al.’s article “Driving Pressure during Thoracic Surgery: A Randomized Clinical Trial” which appeared in March’s edition of Anesthesiology.1 In this double-blinded, prospective study, the intraoperative utilization of driving pressure guided ventilation, in which positive end-expiratory pressure (PEEP) was incrementally titrated to achieve the lowest plateau pressure minus PEEP value at 6 ml/kg tidal volume (VT), reduced the incidence of postoperative pneumonia and acute respiratory distress syndrome following thoracic surgery.1 Despite the success of this study, a potentially important concept which was not evaluated was the optimization of delivered tidal volume (VT) during the transition from two-lung to one-lung ventilation. Per the study protocol, subjects from both arms were ventilated with a fixed VT of 6 ml/kg, throughout all stages of the procedure. As the authors mention, a 6 ml/kg predicted body weight VT target is central to intensive care unit lung-protective ventilation, but the supporting data and practice itself may not be extrapolatable to one-lung ventilation. It is certainly possible that utilization of 6 ml/kg predicted body weight VT during one-lung ventilation could lead to more volutrauma and barotrauma than it would during two-lung ventilation.
Currently there is only sparse literature to guide ventilation, and particularly VT, during one-lung ventilation. Maret et al. found that utilization of VT of 5 ml/kg ideal body weight and 5 to 8 cm H2O of PEEP during one-lung ventilation compared to 10 ml/kg without PEEP resulted in reductions in major postthoracic surgical complications (pneumonia, acute lung injury, acute respiratory distress syndrome, pulmonary embolism, shock, myocardial infarction, or death) and hospital length of stay.2 Similarly, a retrospective study of pneumonectomy patients identified an increasing incidence of postoperative respiratory failure with each 1 ml/kg predicted body weight increase in VT.3 At this time, it is unclear if the outcome benefits of minimization of driving pressure during thoracic surgery would increase, decrease, or remain the same if smaller VT targets were incorporated into the ventilation strategy. For example, targeting a VT of 3 to 4 ml/kg predicted body weight during one-lung ventilation, representing a 50% reduction of VT goals from two-lung ventilation, would be an intuitive approach to maintaining lung-protective ventilation throughout thoracic procedures, but this range has not been studied and could result in undesirable increases in driving pressure as respiratory rate is increased and inspiratory time is decreased to maintain adequate minute ventilation. Further research is needed to determine the optimal VT for one-lung ventilation, with a focus on patient-oriented perioperative outcomes.
Nonetheless, the study group should be applauded for contributing to the growing body of evidence-based medicine which supports utilization of intensive care unit–based lung-protective ventilation strategies in the operating room, and their results certainly support the utilization of driving-pressure guided ventilation during thoracic surgery.
The author declares no competing interests.