Evaluation of transthoracic bioelectrical impedance analysis in monitoring lung water during diuresis

Objective: To evaluate if noninvasive monitoring of lung water by transthoracic bioimpedance analysis adds useful information to standard clinical parameters while diuresing patients with edematous lungs. Design: Prospective, observational study. Setting: University tertiary care teaching hospital. Patients and interventions: Fifty-one healthy controls had right chest transthoracic BIA measured to determine normal right chest resistance and right lung resistivity. Fourteen hospitalized fluid-overloaded patients with edematous lungs were subsequently evaluated by serial right transthoracic BIA measurements before and after four days of diuresis. Measurements and main results: Although right transthoracic resistances were significantly higher in healthy women than men, there were no significant between-sex differences in calculated right lung resistivities. Combined male and female right lung resistivities were normally distributed. Natural log conversion of chest resistivity (named t-BIA) yielded a mean of 6.54 ± 0.23, with a coefficient of variation of 3.5%. Hospitalized patients had right lung t-BIAs significantly lower than normals before diuresis (6.22 ± 0.48; p < 0.01). After diuresis, these rose into the normal range (6.40 ± 0.51). Eight patients (57%) had an increase in chest resistivity, i.e., drier lungs and weight loss. Four patients (29%) who lost weight had wetter lungs and two patients (14%) who gained weight had drier lungs. Chest resistivity changes did not correlate with changes in body weight, chest exam or fluid balance. Conclusion: During diuresis, t-BIA measured changes in lung water add useful additional information to standard clinical parameters by both monitoring the dynamic changes that occur during treatment and by helping to establish meaningful therapeutic endpoints.