The upper inflection point of the pressure-volume curve - Influence of methodology and of different modes of ventilation

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 cmH(2)O and 22.1+/-4.5 cmH(2)O (p=0.86), respectively; at Vt of 5-6 ml/kg, the static and dynamic UIPs were 26.6+/-4.1 cmH(2)O and 25.5 5 cmH(2)O (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.