Bedside-measurements of electrical impedance tomography and functional residual capacity during positioning therapy in a case of acute respiratory failure

The lungs of patients with Acute Respiratory Failure (ARF) are characterized by reduced lung volume and regional heterogeneity of ventilation distribution. To improve lung volume and ventilation distribution, protective mechanical ventilation with positive end-expiratory pressure (PEEP), recruitment maneuvers, and some adjunct measures like intermittent proning have been recommended. But the continuous monitoring and management of these measures is not possible at bedside. New non-invasive monitoring tools like Electrical Impedance Tomography (EIT) and measurements of Functional Residual Capacity (FRC) by oxygen wash-in/washout have been advocated, but are not established in clinical routine. Thus, evident therapy algorithms are not yet available. The aim of this case study was to describe the ability of EIT and FRC measurement to detect changes in regional ventilation and lung volume in an ARF patient, who was treated by alveolar recruitment maneuver and intermittent prone position. An increase in FRC was observed in parallel of gas exchange improvement immediately after the recruitment. During prone position, FRC decreased constantly while a redistribution of ventilation among dorsal lung regions was detected by EIT. These two tools were compared but without a gold standard. The reported case shows that EIT and FRC measurements are two different methods, which are difficult to compare. As they do not present a good correspondence, the respective results may be under or over estimated but the measures indicated some tendencies. Nevertheless the combination of both could be a meaningful monitoring supplementation in the respiratory therapy of ARF patients.