The upper inflection point of the pressure-volume curve
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Objective. The pressure-volume (P/V) curve has been proposed as a tool to adjust the ventilatory settings in cases of acute respiratory distress syndrome (ARDS). The aim of this study was to test the influence of P/V tracing methodology on the presence and value of the upper inflection point (UIP).
Methods. In 13 medical ARDS patients, the interruption and the automated low flow inflation methods were compared while the patients were ventilated at conventional (10–12 ml/kg) and at low (5–6 ml/kg) tidal volume (Vt). Two levels of inspiratory flow and insufflation time were used (3 and 6 s).
Results. No significant difference in UIP was found between the static and the dynamic methods, whatever the flow used. At Vt 10–12 ml/kg, the static and dynamic UIPs were 22.4±4.4 cmH2O and 22.1±4.5 cmH2O (p=0.86), respectively; at Vt of 5–6 ml/kg, the static and dynamic UIPs were 26.6±4.1 cmH2O and 25.5±5 cmH2O (p=0.34), respectively. Significant differences in UIP were found, in the static and dynamic conditions, between the two levels of Vt (p<0.005): it was lower with the higher Vt, suggesting that UIP is dependent on previous tidal alveolar recruitment.
Conclusion. Interruption and continuous flow techniques gave similar results, but the previous Vt influences the pressure value of the UIP.
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