I read the recent meta-analysis by Songsangvorn et al. on electrical impedance tomography-guided positive end-expiratory pressure (PEEP) titration in acute respiratory distress syndrome (ARDS) with great interest [1]. While I commend the authors for their excellent work, I have some concerns regarding the meta-analysis.
Firstly, most randomized controlled trials typically involve patients being randomized into two or more parallel treatment groups. However, in a crossover trial, patients receive two-period treatments. One particular concern with the crossover design is the risk of a carryover effect, where the treatment effects from the first period persist into the second period [2]. Among the 13 studies included in this meta-analysis, one was a randomized crossover trial that did not incorporate a washout phase, potentially increasing the risk of a carryover effect [3]. In this meta-analysis, the authors did not mention how they handled data from this crossover trial. I suggest conducting a sensitivity analysis by excluding this crossover trial to assess the robustness of their conclusions.
Secondly, while nonrandomized studies should not be disregarded when addressing clinical questions in meta-analyses, it is important to note that nonrandomized studies tend to show larger treatment effects [4], as observed in the current meta-analysis. With a more cautious interpretation, the conclusions could be as follows: contrary to findings from randomized trials, evidence from observational studies suggests that electrical impedance tomography facilitates real-time, individualized PEEP adjustments, improving respiratory system mechanics.
Lastly, by the way, the outcomes of respiratory system mechanics measurements lack units, including lung compliance (ml/cmH2O), mechanical power (J/min), driving pressure (cmH2O), plateau pressure (cmH2O), and PEEP level (cmH2O).
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References
Songsangvorn N, Xu Y, Lu C, Rotstein O, Brochard L, Slutsky AS, Burns KEA, Zhang H (2024) Electrical impedance tomography-guided positive end-expiratory pressure titration in ARDS: a systematic review and meta-analysis. Intensive Care Med. https://doi.org/10.1007/s00134-024-07362-2
Elbourne DR, Altman DG, Higgins JP, Curtin F, Worthington HV, Vail A (2002) Meta-analyses involving cross-over trials: methodological issues. Int J Epidemiol 31:140–149
Jimenez JV, Munroe E, Weirauch AJ, Fiorino K, Culter CA, Nelson K, Labaki WW, Choi PJ, Co I, Standiford TJ, Prescott HC, Hyzy RC (2023) Electric impedance tomography-guided PEEP titration reduces mechanical power in ARDS: a randomized crossover pilot trial. Crit Care 27:21
Ioannidis JP, Haidich AB, Pappa M, Pantazis N, Kokori SI, Tektonidou MG, Contopoulos-Ioannidis DG, Lau J (2001) Comparison of evidence of treatment effects in randomized and nonrandomized studies. JAMA 286:821–830
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Gu, WJ. Concern for meta-analysis combining randomized parallel and cross-over trials. Intensive Care Med (2024). https://doi.org/10.1007/s00134-024-07426-3
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DOI: https://doi.org/10.1007/s00134-024-07426-3