Discussion
pulmonary disease, atelectasis, diaphragmatic contraction
COLLAPSE, PULMONARY DISEASE, ATELECTASIS, POSITIVE
The main findings of this study were: 1.) Dorsal proportion of ventilation occurring during general anesthesia was recruited with increasing spontaneous breathing, whereas the proportion of ventilation decreased in ventral regions. Changing the mode of ventilation from controlled to pressure-supported resulted in a significant reduction of ventilation only in the most ventral region. 2.) Spontaneous breathing after controlled ventilation was associated with a large reduction in end-expiratory volume due to termination of PEEP. 3.) The Global Inhomogeneity index showed homogeneous ventilation distribution of ventilated lung-healthy children.Gunnarsson et al. [In spontaneously breathing patients in the supine position, the dorsal portion of the diaphragm exhibits the greatest movement. Thus a thus a large proportion of ventilation occurs here. Positive pressure ventilation primarily moves the ventral regions of the diaphragm caudally. Therefore, during positive pressure ventilation, the majority of ventilation is distributed in the ventral lung areas [In this study, this effect was investigated in infants and children. The performed exploratory analysis shows significant changes in ventilation distribution during general anesthesia. After induction of anesthesia and under controlled ventilation, the dorsal proportion of ventilation was low. This is probably due to a collapse of dorsal lung areas and increased ventral ventilation. During pressure-supported ventilation, there was already a minimal shift of ventilation towards the dorsal lung areas, although this difference was not significant in the current case series. This dorsal shift was most pronounced at the onset of spontaneous breathing after cessation of ventilation. There was a decrease in ventilation in the ventral areas, because the atelectatic lung areas were recruited. Further studies are needed, but this study provides evidence that controlled ventilation also leads to changes in ventilation distribution in infants, small and older children. Despite the lower weight, dorsal atelectasis with probable ventral lung overdistension may occur, among other reasons, due to the lack of diaphragmatic contraction.During ventilation, positive end-expiratory pressure (PEEP) is applied. This pressure affects the end-expiratory volume of the lungs. As expected, a significant reduction in this volume was detected when comparing the two different modes of mechanical ventilation (with PEEP) and spontaneous breathing (without PEEP). While the change in ventilation mode only had a small effect on the change in end-expiratory lung volume, during spontaneous breathing, end-expiratory lung volume changed significantly and was distributed more evenly in both lung areas. The ventral portion became significantly smaller in favor of the dorsal portion. PEEP both recruited dorsal lung areas and overdistended ventral lung areas. After termination of mechanical ventilation, this PEEP ceased and a reduction in lung volume in these areas was detected. The dorsal tidal ventilation fraction was lower in this study compared with the ventral. Therefore, the dorsal fraction of the decrease in end-expiratory volume after extubation was also smaller than the ventral fraction. Wang et al. [Since all children in this study had no pulmonary disease and were ventilated only for short periods, a roughly homogeneous ventilation distribution can be assumed. This could be confirmed by the GI calculation. The examined children showed an almost homogeneous ventilation distribution with a GI of 47%. Zhao et al. [