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. In nine anesthetized pigs, repeated lung lavages were performed until a PaO2 of <80 mm Hg was reached. Thereafter, the lungs were recruited according to two different recruitment protocols: the open lung approach and the open lung concept. Five time points for measurements were chosen: healthy (reference), lavage (atelectasis), recruitment, derecruitment, and maintain recruited (final).

MEASUREMENTS AND MAIN RESULTS

After lavage, there was a significant increase in the impedance ratio, defined as the ventilation-induced impedance changes 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 decreased significantly after performing the recruitment protocol (from 4.51 +/- 2.22 to 1.18 +/- 0.51). During both recruitment procedures, a steep increase in baseline impedance change was seen. Furthermore, during derecruitment, a decrease in the slope in baseline impedance change was seen in the posterior part of the lung, whereas the anterior part showed no change.

CONCLUSION

Electrical impedance tomography is a technique that can show impedance changes resembling recruitment and derecruitment of alveoli in the anterior and posterior parts of the lung. Therefore, electrical impedance tomography may help in determining the optimal mechanical ventilation in a patient with acute lung injury.