۱٫۱٫ Scientific background

On Intensive Care Units (ICUs), respiratory dysfunction due to several causes ranks among the most important clinical problems. Acute respiratory distress syndrome (ARDS) remains frequent and still results in a high mortality [1]. One of the essential parameters in mechanical ventilation is the tidal volume (VT), defined as the gas volume the ventilator moves into the lungs during each respiratory cycle. Over the years, different strategies of adjusting VT have been discussed [2]. In 1963, Bendixen et al. proposed the use of high VT settings above 10 ml per kg predicted body weight (PBW) in order to prevent acidosis and atelectasis, and to improve oxygenation [3]. In later studies, however, such high VT turned out to be harmful and to increase mortality [4] by causing “ventilator induced lung injury” [۵], which led to the concept of the “baby lung” [۶]. Special lung-protective ventilation strategies advise a lower VT setting (6-8 ml/kg PBW) to reduce pulmonary side effects of mechanical ventilation and thus mortality [2]. This recommendation seems to protect not only patients with severe lung injuries, but anyone in need of mechanical ventilation [e.g. 7, 8, 9, 10, 11, 12]. Integrating these concepts into ICU routines, however, can be difficult and informationintensive insofar as frequently updated VT settings have to consider patient-specific threshold parameters. Taking the importance of this parameter into account during everyday care depends on intensive staff training, while reminders and electronic support generally promise to improve awareness.

۱٫۲ Rationale for the study

Accurate lung-protective ventilation requires calculating patient-specific VT recommendations from PBW, which in turn is estimated by a linear formula from patient sex and height [2, 13]. In addition to potential side effects of low-volume ventilation, the ”difficulty [of] calculating tidal volume” is seen as a potential obstacle for a systematic adherence in daily practice [14]. Moreover, the parameters of mechanical ventilation have to be closely monitored over time and if necessary adjusted, because dynamic factors such as supine or prone positioning, fluid balance and edema, neuromuscular blocking, and sedation can influence thoracic compliance and therefore VT (depending on the ventilation mode used). These determinants certainly contribute to the observation that “the protective ventilation strategy is often under-utilized as a therapeutic option, even in ARDS” [۷].