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Acute Lung Injury: Effects of Prone Positioning on Cephalocaudal Distribution of Lung Inflation—CT Assessment in Dogs¹

¹ From the Department of Radiology and Clinical Research Institute, Seoul National University Hospital and the Institute of Radiation Medicine, Seoul National University Medical Research Center, 28 Yongon-dong, Chongno-gu, Seoul 110–744, Korea (H.J.L., J.G.I., J.M.G., Y.I.K., M.W.L.); and Departments of Anesthesiology (H.G.R., J.H.B.) and Internal Medicine (C.G.Y.), Seoul National University Hospital, Seoul, Korea. Received June 30, 2003; revision requested September 9; final revision received March 26, 2004; accepted April 15. Supported by 2002 General Research Fund of Seoul National University Hospital. Address correspondence to J.G.I. (e-mail: imjg@snu.ac.kr).

View larger version (26K): [in a new window]   Figure 1. Graph shows PaO2/FiO2 level at six time points of the protocol. In prone group, PaO2/FiO2 at time point of prone positioning for 1 hour to approximately time of return to supine positioning for 1 hour exceeded baseline value. PaO2/FiO2 in prone group was significantly higher than that of supine group at time point of prone positioning for 3 hours. * indicates P value less than .05 in comparison with baseline values. indicates P value less than .05 in comparison with supine group at same time point. Error bars indicate standard deviations.

View larger version (42K): [in a new window]   Figure 2a. Graphs show mean attenuation values as a function of cephalocaudal lung level in (a) prone and (b) supine groups. In normal lung, mean attenuation increased gradually from apex to base. At baseline after oleic acid injection, mean attenuation increased at all levels, and line became steeper than that of normal lung. In prone group (a), prone positioning reversed relationship between mean lung attenuation and cephalocaudal lung height. In prone position, mean attenuation reached maximum at 10 cm above diaphragm and decreased toward the base, thus generally decreasing from apex to base. Repositioning to supine restored cephalocaudal gradient of mean attenuation to similar pattern of baseline. However, slope became gentler than baseline. In supine group (b), graph shows similar pattern to that of baseline. DD = dome of diaphragm.

View larger version (38K): [in a new window]   Figure 2b. Graphs show mean attenuation values as a function of cephalocaudal lung level in (a) prone and (b) supine groups. In normal lung, mean attenuation increased gradually from apex to base. At baseline after oleic acid injection, mean attenuation increased at all levels, and line became steeper than that of normal lung. In prone group (a), prone positioning reversed relationship between mean lung attenuation and cephalocaudal lung height. In prone position, mean attenuation reached maximum at 10 cm above diaphragm and decreased toward the base, thus generally decreasing from apex to base. Repositioning to supine restored cephalocaudal gradient of mean attenuation to similar pattern of baseline. However, slope became gentler than baseline. In supine group (b), graph shows similar pattern to that of baseline. DD = dome of diaphragm.

View larger version (45K): [in a new window]   Figure 3a. Distribution of gas and tissue along cephalocaudal axis. (a) In normal lung, volume of gas was larger than volume of tissue. (b) At baseline, volume of tissue increased and volume of gas decreased in all levels of lung. Gas was located predominantly in upper lung, whereas tissue was predominant in caudal lung regions. (c) One hour after prone positioning, compared with findings at baseline, volume of gas decreased in cephalic regions, whereas it increased in caudal regions. At the same time, lung volume below diaphragm was expanded. (d) Return to supine position restored distribution of gas and tissue to similar pattern at baseline. DD = dome of diaphragm.

View larger version (44K): [in a new window]   Figure 3b. Distribution of gas and tissue along cephalocaudal axis. (a) In normal lung, volume of gas was larger than volume of tissue. (b) At baseline, volume of tissue increased and volume of gas decreased in all levels of lung. Gas was located predominantly in upper lung, whereas tissue was predominant in caudal lung regions. (c) One hour after prone positioning, compared with findings at baseline, volume of gas decreased in cephalic regions, whereas it increased in caudal regions. At the same time, lung volume below diaphragm was expanded. (d) Return to supine position restored distribution of gas and tissue to similar pattern at baseline. DD = dome of diaphragm.

View larger version (45K): [in a new window]   Figure 3c. Distribution of gas and tissue along cephalocaudal axis. (a) In normal lung, volume of gas was larger than volume of tissue. (b) At baseline, volume of tissue increased and volume of gas decreased in all levels of lung. Gas was located predominantly in upper lung, whereas tissue was predominant in caudal lung regions. (c) One hour after prone positioning, compared with findings at baseline, volume of gas decreased in cephalic regions, whereas it increased in caudal regions. At the same time, lung volume below diaphragm was expanded. (d) Return to supine position restored distribution of gas and tissue to similar pattern at baseline. DD = dome of diaphragm.

View larger version (45K): [in a new window]   Figure 3d. Distribution of gas and tissue along cephalocaudal axis. (a) In normal lung, volume of gas was larger than volume of tissue. (b) At baseline, volume of tissue increased and volume of gas decreased in all levels of lung. Gas was located predominantly in upper lung, whereas tissue was predominant in caudal lung regions. (c) One hour after prone positioning, compared with findings at baseline, volume of gas decreased in cephalic regions, whereas it increased in caudal regions. At the same time, lung volume below diaphragm was expanded. (d) Return to supine position restored distribution of gas and tissue to similar pattern at baseline. DD = dome of diaphragm.

View larger version (34K): [in a new window]   Figure 4. Ratio of gas and tissue along cephalocaudal axis. At time point of prone positioning for 1 hour, ratio of gas and tissue was more uniform along cephalocaudal axis than at time point of supine positioning for 1 hour. DD = dome of diaphragm.

View larger version (34K): [in a new window]   Figure 5a. Percentage of alveolar expansion along cephalocaudal axis. Zero line indicates cutoff between alveolar expansion and contraction. (a) In prone group, alveolar expansion was observed in caudal regions and was most prominent in lung regions below diaphragmatic cupola. In upper lung, with 5-6 cm above the diaphragm as a turning point, alveolar contraction occurred. (b) In supine group, alveolar expansion induced by low PEEP (3 cm H2O) occurred predominantly in cephalic lung regions. Alveolar contraction was not observed. DD = dome of diaphragm.

View larger version (30K): [in a new window]   Figure 5b. Percentage of alveolar expansion along cephalocaudal axis. Zero line indicates cutoff between alveolar expansion and contraction. (a) In prone group, alveolar expansion was observed in caudal regions and was most prominent in lung regions below diaphragmatic cupola. In upper lung, with 5-6 cm above the diaphragm as a turning point, alveolar contraction occurred. (b) In supine group, alveolar expansion induced by low PEEP (3 cm H2O) occurred predominantly in cephalic lung regions. Alveolar contraction was not observed. DD = dome of diaphragm.

View larger version (127K): [in a new window]   Figure 6a. Sagittal reconstructions of right lung at level of inferior vena cava (left-mediastinal windows, right-lung window) obtained from contiguous CT sections in a representative dog. (a) At baseline with dog in the supine position, edematous lung tissue is located predominantly in dorsal and caudal part of lung. (b) In prone position, caudal displacement of dorsal surface of diaphragm is seen. Aeration in dorsal and caudal part of lung is improved markedly, and attenuation of entire lung is more homogeneous.

View larger version (119K): [in a new window]   Figure 6b. Sagittal reconstructions of right lung at level of inferior vena cava (left-mediastinal windows, right-lung window) obtained from contiguous CT sections in a representative dog. (a) At baseline with dog in the supine position, edematous lung tissue is located predominantly in dorsal and caudal part of lung. (b) In prone position, caudal displacement of dorsal surface of diaphragm is seen. Aeration in dorsal and caudal part of lung is improved markedly, and attenuation of entire lung is more homogeneous.