From ATS 2019: Update on Factors that May Help Predict ILD Outcomes

At the American Thoracic Society Meeting 2019 held May 17 – 22, 2019, in Dallas, Texas, several studies presented during a thematic poster session titled “Idiopathic Interstitial Pneumonia: Natural History” reported characteristics that could be used to help predict outcomes among patients with interstitial lung disease (ILD), including certain factors during mechanical ventilation, white blood cell (WBC) count, and weight loss.

Factors predict mortality during mechanical ventilation

Mechanical ventilation has been shown to be associated with high mortality rates among patients with fibrotic ILD (f-ILD) but there is a dearth of information on patient characteristics at hospital admission and procedural strategies that could improve outcomes. A retrospective study of patients intubated for acute respiratory failure (ARF) identified several factors during mechanical ventilation that predicted mortality in this patient population.

The study included 111 patients (38 with idiopathic pulmonary fibrosis [IPF] and 73 with non-IPF), for whom there were 114 admissions for ARF and placement on mechanical ventilation. Most patients (75%) died while in the hospital. Of the 25% of patients who survived to hospital discharge, 4.5% died within 30 days of discharge and 9% died within one year, leaving 11% who survived past 1 year.

An adjusted analysis revealed several statistically significant predictors of mortality, including P/F ratios within 3 and 48 hours of mechanical ventilation, initial fraction of inspired oxygen, initial mean airway pressure, and higher net volume status. The strongest predictors were vasopressor use (odds ratio [OR]=8.05; P=0.0001) and paralytic use (OR=17.9; P<.001) in the first 24 hours of mechanical ventilation.

WBC count matters

White blood cell count associated with survival. In the abstract for this study, the authors note that inpatient status and elevated white blood cell count (WBC) have both been associated in the past with negative outcomes in IPF. Results of their single-center study of patients hospitalized with IPF found that increased WBC count, vs a low count, was associated with reduced survival. 

The study cohort included 56 IPF patients who were hospitalized at Inova Fairfax Hospital between 2009 and 2018. The cohort had a median WBC count of 11.2 X 10⁹ cells/L at hospital admission (range, 4.4 – 30.0 X 10⁹ cells/L), and this median was used to stratify patients as having a “low” (<11.2 X 10⁹ cells per liter) WBC count or a “high” (>11.2 X 10⁹ cells/L) WBC count.

A high WBC count was associated with a >20-month shorter transplant-free survival compared with a low WBC count (0.5 vs 21.5 months; P=0.005). The reason why high WBC is associated with worse survival is unclear. The study authors propose that an elevated white count could be a surrogate for infection and other inflammatory stressors that affect the disease course in patients with IPF.

BMI augurs ILD outcomes

Weight loss linked to ILD outcomes. The significance of weight loss in patients with ILD has not been studied. Authors of a single-center study presented during this poster session reported that weight loss was associated with decreased survival and pulmonary function among patients with ILD.

The study cohort had 224 patients with ILD, including subtypes such as IPF, connective tissue disease-associated-ILD, and chronic hypersensitivity pneumonitis. Only patients who had 2 or more pulmonary function tests conducted more than 90 days apart were included. Average body mass index (BMI) among patients was 28.2 and average annual decline in BMI, 0.1 kg/m².

In an adjusted analysis, for each annual decline in BMI of 1%, there was a statistically significant increased risk of death (risk ratio [RR]=1.04; 95% CI, 1.01 - 1.08; P=0.005), but no increased risk of ≥10% decline in forced vital capacity (FVC) (RR=1.02; 95% CI, 0.99 - 1.05; P=0.16). Furthermore, the largest effect was seen in patients with at least a 5% annual decline in BMI where increased risk of death was more than 2-fold (RR=2.18; 95% CI, 1.23 - 3.89; P=0.008) and risk of FVC decline nearly 2-fold (RR=1.91; 95% CI, 1.15 - 3.16; P=0.012).

“BMI decline over time is prevalent among patients with ILD and is associated with an increased risk of disease progression, as measured by death and pulmonary function decline,” the study authors wrote.