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

Charach, Gideon MD; Rabinovich, Pavel MD, PhD; Grosskopf, Itamar MD; Weintraub, Moshe MD

Clinical Investigations

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.

From the Department of Internal Medicine “C,” Tel Aviv Sourasky Medical Center, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.

© 2001 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins