Background: The current Berlin definition of acute respiratory distress syndrome (ARDS) uses the PaO2/FiO2 (P/F) ratio to classify severity. However, for the same P/F ratio, a patient on a higher positive end-expiratory pressure (PEEP) may have more severe lung injury than one on a lower PEEP.
Objectives: We designed a new formula, the P/FP ratio, incorporating PEEP into the P/F ratio and multiplying with a correction factor of 10 [(PaO2*10)/(FiO2*PEEP)], to evaluate if it better predicts hospital mortality compared to the P/F ratio post-intubation and to assess the resultant changes in severity classification of ARDS.
目的：我们设计了一个新的公式，P/FP比值，将PEEP纳入P/F Ratio并乘以校正因子10[(PaO2×10)/(FiO2×PEEP)]，以评估它是否比P/F Ratio能更好地预测插管后患者的住院死亡率，并评估由P/FP比值导致的ARDS严重程度分级的变化。
Methods: We categorized patients from a dataset of seven ARDS network trials using the thresholds of ≤ 100 (severe), 101–200 (moderate), and 201–300 (mild) for both P/F (mmHg) and P/FP (mmHg/cmH2O) ratios and evalu- ated hospital mortality using areas under the receiver operating characteristic curves (AUC).
Results: Out of 3,442 patients, 1,057 (30.7%) died. The AUC for mortality was higher for the P/FP ratio than the P/F ratio for PEEP levels > 5 cmH2O: 0.710 (95% CI 0.691–0.730) versus 0.659 (95% CI 0.637–0.681), P < 0.001. Improved AUC was seen with increasing PEEP levels; for PEEP ≥ 18 cmH2O: 0.963 (95% CI 0.947–0.978) versus 0.828 (95% CI 0.765– 0.891), P < 0.001. When the P/FP ratio was used instead of the P/F ratio, 12.5% and 15% of patients with moderate and mild ARDS, respectively, were moved to more severe categories, while 13.9% and 33.6% of patients with severe and moderate ARDS, respectively, were moved to milder categories. The median PEEP and FiO2 were 14 cmH2O and 0.70 for patients reclassified to severe ARDS, and 5 cmH2O and 0.40 for patients reclassified to mild ARDS.
结果：3442例患者中，1057例(30.7%)死亡。当PEEP>5 cmH2O时，P/FP对比P/F Ratio的AUC值分别为0.710(95%CI 0.691~0.730) VS 0.659(95%CI 0.637~0.681)，P<0.001。当PEEP≥18cmH2O时，分别为0.963(95%CI为0.947~0.978) VS 0.828(95%CI为0.765~0.891)，P<0.001。当使用P/FP比值代替P/F Ratio时，轻度和中度ARDS患者分别有15%和12.5%的患者被转到较严重的类型，而中度和重度ARDS患者分别有33.6%和13.9%的患者被转到较轻的类型。重度ARDS患者PEEP和FiO2的中位数分别为14cmH2O和70%，轻度ARDS患者PEEP和FiO2中位数分别为5cmH2O和40%。
Conclusions: The multifactorial P/FP ratio has a greater predictive validity for hospital mortality in ARDS than the P/F ratio. Changes in severity classification with the P/FP ratio reflect both true illness severity and the applied PEEP strategy.