MONITORING PERIOPERATIVE CHANGES IN DISTRIBUTION OF PULMONARY VENTILATION BY FUNCTIONAL ELECTRICAL-IMPEDANCE TOMOGRAPHY

Background: Electrical impedance tomography (EIT) is a noninvasive tec hnique providing cross-sectional images of the thorax. We have tested an extended evaluation procedure, the functional EIT (f-EIT), to ident ify the local shifts of ventilation known to occur during the transiti on between spontaneous, controlled and assisted ventilation modes. Met hods: Ten patients scheduled for elective laparotomy were studied in t he surgical ward, operating theatre and ICU during spontaneous and dif ferent modes of mechanical ventilation. Sixteen ECG electrodes were pl aced on the circumference of the thorax and connected with an EIT devi ce (APT System Mark I, IBEES, Sheffield, UK). Measurements lasting 180 s were per formed and f-EIT images of regional ventilation computed. The geometrical centre of ventilation was determined to quantify the r egional distribution of lung ventilation during individual modes of ve ntilation. Results: F-EIT confirmed the differences in the distributio n of ventilation associated with various modes of artificial ventilati on. Accentuated ventilation of the dependent lung regions was observed during spontaneous breathing, whereas a shift the centre of ventilati on to the nondependent regions was found during controlled ventilation . In the course of assisted ventilation a continuous displacement of t he centre of ventilation back towards the dependent lung regions, cons istent with an increased proportion of spontaneous breathing, was dete cted. Unassisted spontaneous breathing after weaning from mechanical v entilation resulted in a similar ventilation distribution as during ti dal breathing prior to surgery. Conclusion: F-EIT determined the redis tribution of lung ventilation during different modes of mechanical ven tilation. We expect that f-EIT will become a useful noninvasive bedsid e monitoring technique for imaging regional ventilation in pulmonary d iseased patients during mechanical ventilation.