Titrated oxygen requirement and prognostication in idiopathic pulmonary fibrosis

Abstract

The supplemental oxygen flow rate is a common bedside measure of gas exchange impairment. We aimed to determine whether a titrated oxygen requirement (TOR) predicted mortality in idiopathic pulmonary fibrosis (IPF). We examined 104 adults with IPF enrolled in a prospective cohort study and a validation cohort of 151 adults with a variety of interstitial lung diseases (ILDs). The TOR was defined as the lowest oxygen flow rate required to maintain an oxyhaemoglobin saturation of 96% while standing. Cox proportional hazards models and time-dependent receiver operating characteristic curves were used to examine survival time. A higher TOR was associated with a greater mortality rate independent of forced vital capacity and 6-min walk test results in IPF (adjusted hazard ratio (per 1 L·min(-1)) 1.16, 95% CI 1.06-1.27). The TOR was at least as accurate as pulmonary function and 6-min walk testing at predicting 1-yr mortality. Findings were similar in other ILDs. The TOR is a simple, inexpensive bedside measurement that aids prognostication in IPF.

Figures

Figure 1

Study participant flow. ILD = interstitial lung disease; IPF = idiopathic pulmonary fibrosis

Figure 2

Unadjusted survival in the (A) derivation (p for trend = 0.001) and (B) validation (p for trend

Figure 3

Time-dependent receiver operating characteristic curves for the prediction of death within one year in the (A) derivation and (B) validation cohorts. The area under the curve (AUC) for the titrated oxygen requirement is 0.75 in the derivation cohort and 0.70 in the validation cohort. The AUC for the other four variables ranges from 0.60 to 0.70 in the derivation cohort and 0.53 to 0.65 in the validation cohort. Thin solid lines are lines of identity. TOR = titrated oxygen requirement; DLCO = diffusing capacity of carbon monoxide; FVC = forced vital capacity; SpO2 = oxyhemoglobin saturation measured by pulse oximetry; 6MWD = six-minute walk distance

Figure 3

Time-dependent receiver operating characteristic curves for the prediction of death within one year in the (A) derivation and (B) validation cohorts. The area under the curve (AUC) for the titrated oxygen requirement is 0.75 in the derivation cohort and 0.70 in the validation cohort. The AUC for the other four variables ranges from 0.60 to 0.70 in the derivation cohort and 0.53 to 0.65 in the validation cohort. Thin solid lines are lines of identity. TOR = titrated oxygen requirement; DLCO = diffusing capacity of carbon monoxide; FVC = forced vital capacity; SpO2 = oxyhemoglobin saturation measured by pulse oximetry; 6MWD = six-minute walk distance