Monitoring of recruitment and derecruitment by electrical impedance tomography in a model of acute lung injury

Objective: To evaluate a noninvasive system for obtaining information about alveolar recruitment and derecruitment in a model of acute lung injury. Design: Prospective experimental study, Setting: Animal research laboratory. Subjects: Nine anesthetized pigs, Interventions: Electrical impedance tomography measurements were performed. Electrical impedance tomography is an imaging technique that can register the ventilation-induced impedance changes in different parts of the lung. I n nine anesthetized pigs, repeated lung lavages were performed until a Pao( 2) of <80 mm tig was reached. Thereafter, the lungs were recruited accordin g to two different recruitment protocols: the open lung approach and the op en lung concept. Five time points for measurements were chosen: healthy (re ference), ravage (atelectasis), recruitment, derecruitment, and maintain re cruited (final), Measurements and Main Results: After lavage, there was a significant increa se in the impedance ratio, defined as the ventilation-induced impedance cha nges of the anterior part of the lung divided by that of the posterior part (from 1.75 +/- 0.63 to 4.51 +/- 2.22; p < .05), The impedance ratio decrea sed significantly after performing the recruitment protocol (from 4.51 +/- 2.22 to 1.18 +/- 0.51), During both recruitment procedures, a steep increas e in baseline impedance change was seen. Furthermore, during derecruitment, a decrease in the slope in baseline impedance change was seen in the poste rior part of the lung, whereas the anterior part showed no change. Conclusion: Electrical impedance tomography is a technique that can show im pedance changes resembling recruitment and derecruitment of alveoli in the anterior and posterior parts of the lung. Therefore, electrical impedance t omography may help in determining the optimal mechanical ventilation in a p atient with acute lung injury.