The total dead space for FCV was then probably around 78 ml, whereas in PRVC it was only 40 ml. To estimate alveolar ventilation in both setups one must also consider the anatomical dead space, which is 21 ml (assuming 2 ml/kg as for intubated pediatric patients with a mean piglet weight of 10.5 kg). In the PRVC system, considering side-stream capnometry was applied via the capnometry port of the pediatric HME-filter as usual in pediatric care, we measured only 19 ml technical dead space. We consulted the manufacturer's product information on the tube adapter ( 4) and other components in the FCV system, checked the technical dead space experimentally, and found a technical dead space of 57 ml. report that the same 5.5 mm inner diameter tube and (as confirmed by them upon inquiry) the same pediatric HME-filter were used in both groups. In Figure 1 we have listed the parts of the respiratory circuits which geometrically determine the technical dead space. In fact, carbon dioxide removal is very susceptible to changes in apparatus dead space, especially in this weight range ( 2, 3). We fully agree with their assumption and try to give some detailed insights into this issue by replicating the respiratory circuits and calculating the actual dead space effect. already mentioned differences in dead space which may provide an explanation for the somewhat contradictory results. Notwithstanding this, the authors draw overall positive conclusions regarding the clinical applicability and efficacy of FCV. At first sight, this may appear to be strange as better aeration is normally associated with better gas exchange. The results show a slightly better and more homogeneous lung aeration in FCV, but inferior gas exchange compared to PRVC.
This paper provides valuable insights into FCV and associated phenomena at very low tidal volumes.
Recently, Álmos Schranc and colleagues published a most interesting experimental study comparing flow-controlled ventilation (FCV) to pressure-regulated volume-controlled ventilation (PRVC) in a pediatric pig-model of healthy and surfactant depleted, injured lungs ( 1). Flow-controlled ventilation maintains gas exchange and lung aeration in a pediatric model of healthy and injured lungs: a randomized cross-over experimental studyīy Enk D, Spraider P, Abram J, Barnes T.
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