Objective: To compare equal pressure method with pressure-volume curve method to quantify the recruited volume.
Methods: Acute respiratory distress syndrome sheep model was induced by intravenous infusion 3 microg/kg lipopolysaccharide (LPS). Recruited volume of three different levels of positive end-expiratory pressure (PEEP=5, 10, 15 cm H2O) were measured both by pressure-volume curve method and by equal pressure method.
Results: The time needed to measure recruited volume by pressure-volume curve method was 5-6 minutes, which was longer than that of equal pressure method. Recruited volume measured by the two methods increased with PEEP. No significant difference was found between the recruited volume measured by equal pressure method and by equal pressure method at PEEP of 5 cm H2O, they were (25.79+/-20.48) ml vs. (63.26+/-54.57) ml (P>0.05), while recruited volume at PEEP of 10 cm H2O and 15 cm H2O measured by equal pressure method were lower than those measured by the pressure-volume curve method, they were (48.64+/-30.51)ml vs. (148.14+/-85.42)ml and (71.50+/-58.09)ml vs. (322.86+/-148.42)ml (all P<0.05) respectively.
Conclusion: Though equal pressure method is simple, it could not take the place of pressure-volume curve method to quantify recruited volume.