Transthoracic electrical impedance during extracorporeal hemodialysis in acute respiratory failure ("Shocked Lung syndrome")

Abstract

The alteration (delta Z0) of transthoracic electrical impedance (TEI) during extracorporeal hemodialysis (EHD) was investigated in two Groups of patients with acute renal and acute respiratory failure, that differed with respect to the severity of respiratory insufficiency. Group I had moderate respiratory failure (FiO2 0.31 +/- 0.10, PaO2 84 +/- 14 mmHg), and Group II had severe respiratory failure (FiO2 0.75 +/- 0.17, PaO2 77 +/- 14 mmHg). There was a significant correlation between increase in TEI (delta Z0) and decrease in body weight (delta BW) in each individual patient, but the slope of regression lines was remarkably flattened in Group II. In Group I, delta TEI was 1.9 +/- 0.9 omega, the calculated TEI for 500 gr decrease in BW (delta Z0-500 gr) was 0.59 +/- 0.21 omega, and a significant correlation existed between pooled data of delta Z0 and delta BW. In Group II TEI increased less significantly, delta TEI was 0.6 +/- 0.3 omega (P less than 0.001), delta Z0-500 gr was 0.26 +/- 0.27 omega (P less than 0.01), and there was no correlation between pooled data of delta Z0 and delta BW. Increase of TEI in Group II could be completely attributed to increase in hematocrit. It is concluded that patients of Group I with acute renal failure and moderate respiratory failure lost intrathoracic fluid during EHD, whereas patients of Group II with severe respiratory failure did not. TEI during EHD may serve as a test for detection of fixed fluid within the pulmonary interstitium indicating a poor prognosis of the acute respiratory failure.