Objective: To investigate the value of electrical impedance tomography for the assessment of regional lung mechanics during high-frequency oscillatory ventilation (HFOV).
Design: Prospective, interventional animal study.
Setting: University research laboratory.
Subjects: Eight pigs with lavage-induced lung injury.
Interventions: Electrical impedance tomography measurements were performed during a pressure-volume maneuver and during a recruitment-derecruitment maneuver on HFOV by stepwise variation of continuous distending pressure (CDP).
Measurements and main results: Lung volume was estimated by calibrated strain-gauge plethysmography; regional lung volume changes were assessed by electrical impedance tomography in various regions of interest. We found that inflation during the pressure-volume maneuver was distributed nonhomogeneously, whereas deflation was homogeneous. During HFOV, no major regional differences were found during either inflation or deflation. The upper inflection point on the deflation limb was at a slightly higher continuous distending pressure (26+/-3 cm H2O) than the minimal physiologic shunt fraction (at continuous distending pressure of 23+/-7), where there were hemodynamic signs of overdistension. Maximal compliance on the deflation limb (at continuous distending pressure of 13+/-3 cm H2O) agreed well with the minimal continuous distending pressure, where shunt fraction was just below 0.1 (14+/-2 cm H2O).
Conclusions: HFOV has a homogenizing effect on lung volume distribution. Regional lung volume distribution can be assessed using electrical impedance tomography. However, thoracic fluid accumulation may complicate its interpretation.