However, CT is not an adequate method to monitor mechanical ventilation therapy due to radiation and the size of the device.Using EIT instead of CT for bedside assessment of tidal volume distribution is a new trend. As the EIT images alone cannot be used objectively, quantifications were normally Seliciclib structure performed by calculating the ratio between different arbitrarily defined regions of interest [2,31-33]. Erlandsson and colleagues titrated PEEP to maintain a horizontal end-expiratory global relative impedance value, i.e. a stable end-expiratory lung volume, and claimed that such PEEP was optimal [8]. Although the partial pressure of oxygen (PaO2)/FiO2 ratio and compliance finally increased in these patients (not the maxima of PaO2/FIO2), there was no indication that these PEEP levels were optimal.

Besides, how to identify the horizontal baseline has not explained in the literature. Luepschen and colleagues [9] modified the centre of gravity index from Frerichs and colleagues [16,34] to evaluate functional lung opening and overdistension of the lung tissue [9]. Unfortunately, we found more than one single minimum with their method on our data. This may be due to the differences in state of the lungs (healthy vs. lavage) or the differences in species (human vs. animal). Luepschen and colleagues also found that significant differences between dependent and non-dependent tidal volume loss and gain may reliably indicate recruitment and derecruitment of lung tissue [9]. But because they divided the EIT images into only two parts – a dorsal and a ventral – changes within each part were not detectable, leading to a coarse-grained method.

Unlike the global lung mechanics and static P/V curve, which are restricted to information integrating all lung regions [3], the GI index describes the inhomogeneity of tidal volume distribution in a cross-sectional lung plane where the EIT belt was placed in detail up to 32 �� 32 regions. At the same time, with the help of a robust lung area determination method [10,14], the inhomogeneity analysis is restricted only to the lung region. Cardiac-related area and thorax area are excluded [10,14]. In addition, the GI index is a completely maneuver-free tool although in the present study an incremental PEEP trial was used. Without running the risk of inducing lung overinflation and ventilator-induced lung injury, PEEP may be adjusted according to the GI value.

By adding small changes of PEEP, the gradient of the GI value indicates the direction of beneficial PEEP alteration.Although a potential link between Drug_discovery the homogeneity of air distribution in the lungs and dynamic respiratory mechanics is foreseen, a reference method to verify the homogeneity, such as CT, was missing in the study due to ethical reasons. Concrete evidence must be found to prove this relation or further validation with CT is needed before clinical application.