Impact of cardiac output and alveolar ventilation in estimating ventilation/perfusion mismatch in ARDS using electrical impedance tomography

Abstract Introduction Electrical impedance tomography (EIT) can be used to assess ventilation/perfusion (V/Q) mismatch within the lungs. Several methods have been proposed, some of them neglecting the absolute value of alveolar ventilation (V A) and cardiac output (Q C). Whether this omission results in acceptable bias is unknown. Methods Pixel-level V/Q maps of 25 ARDS patients were computed once considering (absolute V/Q map) and once neglecting (relative V/Q map) the value of Q C and V A. Previously published indices of V/Q mismatch were computed using absolute V/Q maps and relative V/Q maps. Indices computed with relative V/Q maps were compared to their counterparts computed using absolute V/Q maps. Results Among 21 patients with ratio of alveolar ventilation to cardiac output (V A/Q C) > 1, relative shunt fraction was significantly higher than absolute shunt fraction [37% (24–66) vs 19% (11–46), respectively, p