Re: Digital chest drainage is better than traditional chest drainage following pulmonary surgery: a meta-analysis

In this issue of the European Journal of Cardio-Thoracic Surgery, Zhou et al. [1], in a well-conducted meta-analysis, concluded that using digital chest drainage systems might be necessary to reduce air leak and hospital stay after pulmonary surgery. As systematic reviews on randomized controlled trials are placed at the top of the hierarchy of evidence [2], the question is, should the use of digital pleural drainage systems be recommended as a routine after lung resection? The answer is no; or, at least, the evidence is inconclusive. To the best of our knowledge, when compared with the systematic review published in 2014 by Afoke et al. [3], the current meta-analysis still does not give an answer to the question.

Although the authors have conducted a credible review and meta-analysis, we would like to suggest a few points that should be considered by the readers of the article by Zhou et al. [1].

The first one is related to the outcomes. The authors have selected 3 main outcomes to be analysed: time to chest tube withdrawal, duration of air leak and hospital stay. No conclusions can be expected regarding the first one due to the heterogenous amount of pleural fluid ranging 200–450 ml in 24 h to pull out chest tubes as stated in the articles included in the meta-analysis. The other 2 outcomes could be considered as the same because air leak is the main variable influencing hospital stay after lung resection [4]; indeed, in pulmonary surgery, hospital stay is a surrogate to the duration of an air leak. In a previous article [5], we have concluded that the use of digital drainage systems improved the observers’ agreement to withdraw chest tubes. Better interobserver agreement could be linked to shorter time with chest tubes and, consequently, shorter hospital stay. In addition, digital monitoring of air leaks could be useful for predicting prolonged air leak, allowing earlier discharge with portable drainage units [6], and, hence, electronic systems could be linked to shorter hospital stay. However, as the occurrence of prolonged air leak can also be accurately performed using conventional drainage systems [7], the recommendation to use more expensive ones is arguable.

The second point is how much more the length of hospital stay is reduced using digital chambers? If we carefully analyse data offered by the authors, in only 3 of 10 trials, the length of hospital stay was decreased by 1 day or more [8–10], and one of those trials [8] should have been excluded from the analysis since in most of the cases in the series, surgery was not indicated. Thus, the differences in length of staging between patients with digital and analogical devices (in operated patients) ranged 0–1 with a median of 0.7 days (<17 h); in other words, patients could be discharged in the evening instead of staying overnight.

According to the GRADE approach [11], using digital devices for pleural drainage cannot be considered a strong recommendation. We doubt that most clinicians, patients and policy makers would select a policy of digital control of chest tubes after knowing that the procedure does not improve primary outcomes (postoperative mortality, morbidity and quality of life) and that the only advantage is that non-complicated patients will be probably discharged home 17 h earlier.

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