Transthoracic monitoring of the impedance of the right lung in patients with cardiogenic pulmonary edema

Objective: To evaluate the suitability of the new electrical impedance monitor RS-205 for monitoring of cardiogenic pulmonary edema (CPE). Design: Prospective, controlled study. Setting: A department of internal medicine in a 1,200-bed university-affiliated, teaching hospital. Patients: Sixty patients, aged 52-80 yrs, 30 without CPE (controls) and 30 with or at high risk for CPE. Interventions: Internal thoracic impedance (ITI) was monitored by the RS-205. The RS-205 is approximately three times more sensitive than the Kubicek monitor, and it eliminates the effect of the drift of skin-to-electrode impedance. This is achieved by eliminating skin electrode impedance by a special algorithm, thus allowing measurement of ITI rather than total transthoracic impedance. Measuring ITI, the main component of which is lung impedance, is a noninvasive and safe method. CPE was diagnosed in accordance with well-accepted clinical and roentgenological criteria. Measurements and Main Results: The controls' initial ITI was 68.3 +/- 12.38 ohms. During 6 hrs of monitoring, the ITI attained a minimum average value of -1.3 +/- 2.08% and a maximum average value of 4.6 +/- 3.56% relative to baseline. In all patients entering CPE, ITI decreased by 14.4 +/- 5.42% on the average (p < .001) 1 hr before the appearance of clinical symptoms. In patients with evolving CPE, ITI decreased significantly compared with controls (22.25 +/- 9.82%, p < .001). In patients at the peak of pulmonary edema, ITI was 2.1 times lower than in the control group (33.1 +/- 10.90 ohms, p < .001). In the last hour before the resolution of CPE, ITI increased in all patients by 17.7 +/- 19.74% compared with the peak of disease (p < .05). After the resolution of pulmonary edema, ITI increased in all patients by 44.14 +/- 26.90% compared with the peak of disease (p < .001). Importantly, the trend in ITI in all patients changed in accordance with the dynamics of CPE. A mixed general linear model shows that ITI values correlated well with the degree of crepitation, a direct characteristics of CPE. Conclusions: The RS-205 is suitable for monitoring patients at high risk of CPE development. It enables detection of CPE and the monitoring of patients at all stages of CPE.