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Abstract
BackgroundIn acute respiratory distress syndrome (ARDS), gas exchange and respiratory system mechanics (compliance) are severely impaired. Besides ventilatory parameters, the degree of respiratory abnormality can be influenced by the circulatory state. This study investigated the influence of acute hypovolemia on the respiratory system.MethodsWe performed a secondary analysis of a previous study including 8 pigs with ARDS-like syndrome induced by lung lavage and surfactant depletion method (ARDS group) and 10 mechanically ventilated pigs with no intervention (CTRL group). Animals of both groups were subjected to hemorrhage and retransfusion successively. We reanalyzed the effect of acute blood volume variations on intrapulmonary shunt (shunt), arterial oxygenation (PaO2:FiO2), global oxygen delivery (DO2) and respiratory system compliance (Crs).ResultsIn the ARDS group, after hemorrhage, shunt decreased (−28 +/− 3.5 % (p < 0.001)), respiratory system compliance (Crs) increased (+5.1 +/− 1.0 ml/cm H2O (p < 0.001)) moreover, there was a concurrent increase in PaO2:FiO2 (+113 +/− 19.1 mmHg; p < 0.001) but this did not prevent a reduction in DO2 (−317 +/− 49.8 ml/min; p < 0.001). Following retransfusion, shunt and Crs return towards pre-hemorrhage values. Similar changes, but of smaller magnitude were observed in the CTRL group, except that no significant changes in oxygenation occurred.ConclusionsThe present analysis suggests that an acute decrease in blood volume results in a decrease in shunt with a parallel improvement in arterial oxygenation and an increase in Crs during ARDS-like syndrome. Our results strengthen the importance to integrate the circulatory condition in the analysis of the state of the respiratory system. However, the translation of this physiological model in a clinical perspective is not straightforward because our model of acute and severe hemorrhage is not strictly equivalent to a progressive hypovolemia, as could be obtained in ICU by diuretic. Furthermore, the present model does not consider the impact of blood loss induced decrease of DO2 on other vital organs function.Trial registration‘Not applicable’.
Highlights
In acute respiratory distress syndrome (ARDS), gas exchange and respiratory system mechanics are severely impaired
In a previous study exploring the influence of tidal volume (VT) and respiratory rate (RR) on pulse pressure variations in pigs with ARDS [17], we observed an unexpected improvement in oxygenation and an increase in respiratory system compliance (Crs) during acute hemorrhage
cardiac output (CO) (Figs. 1 and 2), mean arterial pressure and central venous pressure (CVP) decreased during the hemorrhage and recovered to baseline values during retransfusion (Table 3)
Summary
In acute respiratory distress syndrome (ARDS), gas exchange and respiratory system mechanics (compliance) are severely impaired. Several studies explored the influence of ventilation parameters during acute respiratory distress syndrome (ARDS) [1, 2]. Concerning the respiratory system compliance (Crs), previous studies reported conflicting results as some observed an increase [12, 13], a decrease [5] or no significant changes [14, 15] in Crs related to hemorrhage. An increase in pulmonary blood volume has been shown to result in a decrease in lung compliance [16]. In a previous study exploring the influence of tidal volume (VT) and respiratory rate (RR) on pulse pressure variations in pigs with ARDS [17], we observed an unexpected improvement in oxygenation and an increase in Crs during acute hemorrhage. In order to complete previous studies on this issue, we analyzed retrospectively our data with the hypothesis that a decrease in CO due to hypovolemia, may decrease intrapulmonary shunt, improve Crs and may result in an improvement in arterial oxygenation during ARDS
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