Raw Bioelectrical Impedance Analysis Variables are Independent predictors of Early All-Cause Mortality in Patients With COPD.

BACKGROUND: Bioelectrical impedance analysis is a valuable method for estimating fat-free mass (FFM) and fat mass (FM) in COPD patients by means of specific predictive equations. In addition, raw BIA variables such as high to low frequency impedance ratios (IRs) and phase angle, most likely as a result of providing information on muscle quality, have been related to disease severity and mortality in patients suffering from several diseases, but never in COPD. The aim of this study was to investigate the predictive role of raw BIA variables on two-year survival in COPD.

METHODS: Impedance (Z) at 5-10-50-100-250 kHz and phase angle at 50 kHz were determined in 210 COPD patients. Three IRs were calculated: Z at 50 kHz/Z at 5 kHz (50/5 IR), Z at 100 kHz/Z at 5 kHz (100/5 IR) and Z at 250 kHz/Z at 5 kHz (250/5 IR). Demographical, respiratory and body composition data at the baseline were recorded. All-cause mortality was assessed during 2 years of follow-up.

RESULTS: After the follow up period, all-cause mortality was 13.8%. Statistically significant differences between non-survivors and survivors emerged in terms of age, weight, BMI, FEV1, inspiratory capacity (IC), mMRC dyspnea score. With respect to nutritional variables, non-survivors had lower FFM (P=0.031), lower FM (P=0.015), higher IRs (P<0.001 for all the ratios) and lower phase angle (P<0.001) compared to survivors. After adjustment for confounding factors, each unit increase of IRs and each unit decrease of phase angle was associated with a higher risk of death.

CONCLUSIONS: Impedance ratios and phase angle, as raw BIA variables, are independent and powerful predictors of all-cause mortality in COPD and should be considered, together with inspiratory capacity and 6MWD, as significant prognostic factors in the short-middle term.