To the Editor:
I read with interest the randomized clinical trial by Park et al.1 on the novel approach of using driving pressure–guided ventilation during one-lung ventilation as a method to reduce postoperative pulmonary complications in comparison to conventional protective ventilation. There are several significant limitations to the study that impact interpretation of the results and conclusions. First, the inclusion of lung resection and esophagectomy patients in assessing the effects of driving pressure manipulations on combined pulmonary outcomes is the most important limitation of this study. In comparison to lung resections, esophagectomies are different in that preoperative chemoradiation is standard, the operation typically involves an abdominal and/or neck incision in addition to the thoracic approach, intraoperative ventilation includes a significant period of two-lung ventilation, and there are greater fluid requirements, as well as higher risks of aspiration and greater postoperative morbidity and mortality.2,3 The Society of Thoracic Surgeons (Chicago, Illinois) maintains two separate databases for these operations. For example, the reported incidence of pneumonia within 30 days of lung resection is 4.8% (1,116 of 27,844)2 and 12.2% (529 of 4,321)3 after esophagectomy. Similar to the authors’ efforts to focus on the effects of intraoperative ventilatory parameters during one-lung ventilation on the combined incidence of postoperative pneumonia and/or acute respiratory distress syndrome (ARDS), we reported an overall incidence of 4.0% (24 of 608) following anatomic lung resection.4 It would be more informative if the authors could share their outcome data by the type of surgery and not combined as presented even if the results were negative.
Second, in the third paragraph of the results and in figure 2, a chi-square test was incorrectly used for analyzing the incidence of ARDS between the driving pressure group and protective ventilation group (0 of 145 vs. 5 of 147; P = 0.025) where it would have been more appropriate to use the Fisher exact test of this result which would yield a nonsignificant P = 0.060 value. Third, the authors discuss the importance of finding a median difference of 1 cm H2O lower in the driving pressure group versus the protective ventilation group as being associated with a lower incidence of pulmonary complications (fig. 2),1 however, with the exception of the incidence of ARDS which was not statistically significant (as mentioned previously), pneumonia occurred more frequently in the operated (nonventilated) lung compared to that of the ventilated lung in either group, theoretically protected by a lower driving pressure. Finally, although the two patient groups were well matched with respect to preoperative baseline characteristics, it would be interesting to know, regardless of group assignment, whether major pulmonary complications after lung resection only were associated with proven and independent negative prognostic factors5,6 such as reduced preoperative diffusion capacity of carbon monoxide, preoperative chemotherapy, and increasing intraoperative fluid administration.
The author declares no competing interests.