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An Objective Analysis of the Pressure-Volume Curve in the Acute Respiratory Distress Syndrome

2000; American Thoracic Society; Volume: 161; Issue: 2 Linguagem: Inglês

10.1164/ajrccm.161.2.9901061

1535-4970

R. Scott Harris, Dean Hess, José G. Venegas,

Neonatal Respiratory Health Research

To assess the interobserver and intraobserver variability in the clinical evaluation of the quasi-static pressure-volume (P-V) curve, we analyzed 24 sets of inflation and deflation P-V curves obtained from patients with ARDS. We used a recently described sigmoidal equation to curve-fit the P-V data sets and objectively define the point of maximum compliance increase of the inflation limb (Pmci,i) and the true inflection point of the deflation limb (Pinf,d). These points were compared with graphic determinations of lower Pflex by seven clinicians. The graphic and curve-fitting methods were also compared for their ability to reproduce the same parameter value in data sets with reduced number of data points. The sigmoidal equation fit the P-V data with great accuracy (R2 = 0.9992). The average of Pflex determinations was found to be correlated with Pmci,i (R = 0.89) and Pinf,d (R = 0.76). Individual determinations of Pflex were less correlated with the corresponding objective parameters (R = 0.67 and 0.62, respectively). Pflex + 2 cm H2O was a more accurate estimator of Pinf,d (2 SD = ± 6.05 cm H2O) than Pflex was of Pmci,i (2 SD = ± 8.02 cm H2O). There was significant interobserver variability in Pflex, with a maximum difference of 11 cm H2O for the same patient (SD = 1.9 cm H2O). Clinicians had difficulty reproducing Pflex in smaller data sets with differences as great as 17 cm H2O (SD = 2.8 cm H2O). In contrast, the curve-fitting method reproduced Pmci,i with great accuracy in reduced data sets (maximum difference of 1.5 cm H2O and SD = 0.3 cm H2O). We conclude that Pflex rarely coincided with the point of maximum compliance increase defined by a sigmoid curve-fit with large differences in Pflex seen both among and within observers. Calculating objective parameters such as Pmci,i or Pinf,d from curve-fitted P-V data can minimize this large variability. Harris RS, Hess DR, Venegas JG. An objective analysis of the pressure-volume curve in the acute respiratory distress syndrome.