Thoracic impedance vs chest radiograph to diagnose acute pulmonary edema in the ED

We sought to investigate the relationship between thoracic impedance (Zo) and pulmonary edema on chest radiography in patients presenting to the emergency department (ED) with signs and symptoms of acute decompensated heart failure (ADHF).

This was a prospective, blinded convenience sample of patients with signs and symptoms of ADHF who underwent measurement of Zo with concomitant chest radiography. Attending physicians blinded to the Zo values interpreted the radiographs, categorizing the severity of pulmonary edema as normal (NL), cephalization (CZ), interstitial edema (IE), or alveolar edema (AE). Intergroup comparisons were analyzed with a 2-way analysis of variance (ANOVA), with P < .05 considered statistically significant and reported using 95% confidence intervals (CIs).

We enrolled patients (> or =18 years) presenting to a tertiary care medical center ED with signs and symptoms consistent with ADHF.

A total of 203 patients were enrolled, with 27 (14%) excluded because of coexisting pulmonary diseases. The mean Zo values were inversely related to the 4 varying degrees of radiographic pulmonary vascular congestion as follows: NL, 25.6 (95% CI, 22.9-28.3); CZ, 20.8 (95% CI, 18.1-23.5); IE, 18.0 (95% CI, 16.3-19.7); and with AE, 14.5 (95% CI, 12.8-16.2) (ANOVA, P < .04). A Zo less than 19.0 ohms had 90% sensitivity and 94% specificity (likelihood ratio [LR], - 0.1; LR + 15) for identifying radiographic findings consistent with pulmonary edema. Females had an increased mean Zo value compared to males (P < .03).

The Zo value obtained via thoracic bioimpedance monitoring accurately predicts the presence and severity of pulmonary edema found on initial chest radiograph in patients suspected of ADHF.