Prognostic value of respiratory index in haemodynamically stable patients with acute pulmonary embolism: The Respiratory Index model study

Background: Current strategies for prognostic stratification in haemodynamically stable patients with acute pulmonary embolism require improvement. The aims of this study in haemodynamically stable patients with acute pulmonary embolism were (a) to evaluate the prognostic value of a novel respiratory index (oxygen saturation in air to respiratory rate ratio) and (b) to derive a risk model which includes the respiratory index and evaluate its value in predicting 30-day mortality. Methods: Prospective cohorts of haemodynamically stable patients with acute pulmonary embolism were merged to a collaborative database that served to create two subsequent derivation and validation cohorts based on a temporal criterion. The study outcome was 30-day all-cause death. Results: Thirty-day all-cause death occurred in 7.5% and in 6.9% of patients in the derivation and validation cohorts (each composed of 319 patients). In the derivation cohort, the respiratory index (odds ratio 0.66, 95% confidence interval 0.48-0.90) and simplified Pulmonary Embolism Severity Index (odds ratio 9.16, 95% confidence interval 1.22-68.89) were predictors of 30-day mortality. The cut-off value of the respiratory index <= 3.8 was identified to best predict 30-day all-cause death (15.4% vs 5.0%, odds ratio 2.94, 95% confidence interval 1.22-7.11). The respiratory index <= 3.8 was combined with the simplified Pulmonary Embolism Severity Index to create the Respiratory Index model that showed a good discriminatory power in the derivation (c-statistic 0.703, 95% confidence interval 0.60-0.80) and in the validation cohort (c-statistic 0.838, 95% confidence interval 0.768-0.907). Conclusion: In hemodynamically stable patients with acute pulmonary embolism, the respiratory index was an independent predictor of 30-day all-cause death. The Respiratory Index model which includes the simplified Pulmonary Embolism Severity Index and the respiratory index, provides a good risk stratification of haemodynamically stable patients with acute pulmonary embolism.