Tidal recruitment assessed by electrical impedance tomography and computed tomography in a porcine model of lung injury*.
OBJECTIVE
To determine the validity of electrical impedance tomography to detect and quantify the amount of tidal recruitment caused by different positive end-expiratory pressure levels in a porcine acute lung injury model.


METHODS
Randomized, controlled, prospective experimental study.


METHODS
Academic research laboratory.


METHODS
Twelve anesthetized and mechanically ventilated pigs.


METHODS
Acute lung injury was induced by central venous oleic acid injection and abdominal hypertension in seven animals. Five healthy pigs served as control group. Animals were ventilated with positive end-expiratory pressure of 0, 5, 10, 15, 20, and 25 cm H2O, respectively, in a randomized order.


RESULTS
At any positive end-expiratory pressure level, electrical impedance tomography was obtained during a slow inflation of 12 mL/kg of body weight. Regional-ventilation-delay indices quantifying the time until a lung region reaches a certain amount of impedance change were calculated for lung quadrants and for every single electrical impedance tomography pixel, respectively. Pixel-wise calculated regional-ventilation-delay indices were plotted in a color-coded regional-ventilation-delay map. Regional-ventilation-delay inhomogeneity that quantifies heterogeneity of ventilation time courses was evaluated by calculating the scatter of all pixel-wise calculated regional-ventilation-delay indices. End-expiratory and end-inspiratory computed tomography scans were performed at each positive end-expiratory pressure level to quantify tidal recruitment of the lung. Tidal recruitment showed a moderate inter-individual (r = .54; p < .05) and intra-individual linear correlation (r = .46 up to r = .73 and p < .05, respectively) with regional-ventilation-delay obtained from lung quadrants. Regional-ventilation-delay inhomogeneity was excellently correlated with tidal recruitment intra- (r = .90 up to r = .99 and p < .05, respectively) and inter-individually (r = .90; p < .001).


CONCLUSIONS
Regional-ventilation-delay can be noninvasively measured by electrical impedance tomography during a slow inflation of 12 mL/kg of body weight and visualized using ventilation delay maps. Our experimental data suggest that the impedance tomography-based analysis of regional-ventilation-delay inhomogeneity provides a good estimate of the amount of tidal recruitment and may be useful to individualize ventilatory settings.
Department of Anesthesiology and Intensive Care Medicine, University of Bonn, Bonn, Germany. t.muders@uni-bonn.de
Thomas
T
Muders
Henning
H
Luepschen
Jörg
J
Zinserling
Susanne
S
Greschus
Rolf
R
Fimmers
Ulf
U
Guenther
Miriam
M
Buchwald
Daniel
D
Grigutsch
Steffen
S
Leonhardt
Christian
C
Putensen
Hermann
H
Wrigge
D000818:Animals; D017097:Electric Impedance; D055370:Lung Injury / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D011175:Positive-Pressure Respiration; D013552:Swine; D013990:Tidal Volume; D014057:Tomography, X-Ray Computed