![]() Estimated VDphysiol/VT ratios systematically underestimated measured VDphysiol/VT ratios.Īshbaugh DG, Bigelow DB, Petty TL, Levine BE. The respiratory response to PP appeared more relevant when PaCO2 rather than the PaO2/FiO2 ratio was used. PP induced a decrease in VDalv/VT ratio and an improvement in respiratory mechanics. Estimated VDphysiol/VT ratios significantly underestimated measured VDphysiol/VT ratios (concordance correlation coefficient 0.19 (interquartile ranges 0.091 to 0.28)), whereas changes during PP were more reliable (concordance correlation coefficient 0.51 (0.32 to 0.66)). ![]() When the response was defined by PaCO2, four patients were differently classified, and responders (n = 7) had a greater decrease in VDalv/VT ratio and in Pplat and a greater increase in PaO2/FiO2 ratio and in Crs than nonresponders (n = 6). When the response was defined by PaO2/FiO2 ratio, no significant differences in Pplat, PaCO2 or VDalv/VT alterations between responders (n = 7) and nonresponders (n = 6) were observed. Changes in VDalv/VT were correlated with changes in Crs, but not with changes in PaO2/FiO2 ratios. Maximal changes were observed after six to nine hours. PP induced a decrease in Pplat, PaCO2 and VDalv/VT ratio and increases in PaO2/FiO2 ratios and compliance of the respiratory system (Crs). Estimated and measured VDphysiol/VT ratios were compared. Thirteen patients with a PaO2/FiO2 ratio 20 mmHg or by a decrease in PaCO2 > 2 mmHg. We also aimed to validate a recently proposed method of estimation of the physiological dead space (VDphysiol/VT) without measurement of expired CO2. Our aims in this study were to report changes in the ratio of alveolar dead space to tidal volume (VDalv/VT) in the prone position (PP) and to test whether changes in partial pressure of arterial CO2 (PaCO2) may be more relevant than changes in the ratio of partial pressure of arterial O2 to fraction of inspired O2 (PaO2/FiO2) in defining the respiratory response to PP.
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