Fibrotic idiopathic interstitial pneumonias: mortality is linked to a decline in gas transfer

Baseline clinical and physiological features and changes in these parameters over time are known predictors of survival in patients with fibrotic idiopathic interstitial pneumonia (IIP). Pulmonary hypertension is common in advanced fibrotic IIP, and has a negative impact on survival. Serial pulmonary function profiles, indicative of increasing vascular impairment in patients with IIP, and in particular, selective reductions in gas transfer, have not been studied previously.

Predictors of event-free survival time were investigated in a cohort of Dutch patients with IPF and fibrotic non-specific interstitial pneumonia (n = 117). Pulmonary function test data were prospectively collected from November 1993 to December 2005. Multivariate Cox regression models were developed to identify the prognostic relevance to survival of variables related to baseline demographics, histopathology, pulmonary function and the 6- and 12-month changes in pulmonary function parameters.

Different survival patterns were observed for patients with different histopathological diagnoses. At baseline, FVC was the most important prognostic factor. At the 6-month follow up, change in transfer coefficient (K(CO), DL(CO)/V(A)), and at the 12-month follow up, age, baseline K(CO) and 12-month change in FVC and K(CO), were independent predictors of event-free survival.

Apart from histopathology, change in K(CO) over time appeared to be the most consistent and powerful predictor of survival in these patients. The decline in K(CO) may be indicative of increasing vascular impairment, which may have a major impact on survival, in patients with fibrotic IIP.