Meeting Abstracts
» Effects of Prone Position on the Cephalocaudal Distribution of Lung Inflation during Acute Lung Injury: A Computed Tomographic Assessment in Dogs

Hyun Ju Lee, MD1, Jung-Gi Im, MD2, Jin Mo Goo, MD2, Young Il Kim2, MD, Min Woo Lee, MD2, Ho-Geol Ryu, MD3, Jae-Hyon Bahk, MD3.

1 Department of Radiology, Gachon Medical School, Gil Medical Center, 1198, Kuwol-dong, Namdong-gu, Incheon 405-220, Korea
2 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
3 Department of Anesthesiology, Seoul National University Hospital

This study was supported by year 2002 General Research Fund of Seoul National University Hospital.

Correspondence to Jung-Gi Im, MD.
Seoul National University College of Medicine, 28 Yongon-dong, Chongno-gu, Seoul 110-744, Korea
Tel: (822) 760-2584
Fax: (822) 743-6385
E-mail: imjg@radcom.snu.ac.kr

PURPOSE: To evaluate the cephalocaudal distribution of gas/tissue proportions and inflation gradient of the lung in acute lung injury (ALI).

MATERIALS AND METHODS: After induction of ALI by the intravenous injection of oleic acid, we randomized the dogs to be ventilated to either the prone (n=6) or the supine (n=6) positions. Spiral CT and hemodynamic measurement were performed sequentially hourly. Volume and mean attenuation of the lung were quantitatively measured using PC-based software in each CT section. The cephalocaudal gradient of mean lung attenuation, distribution of gas/tissue, and alveolar expansion were assessed. Functional residual capacity and net alveolar expansion of the entire lung were measured.

RESULTS: Mean lung attenuation gradually increased from the apex to the base of the lung in the supine position. Thus an inflation gradient along the cephalocaudal axis was found. Gas was predominantly located in the upper lung, whereas tissue was dominant in the lower lung in the supine position. After prone positioning, the cephalocaudal inflation gradient was reduced and the gas/tissue proportion became more uniform along the cephalocaudal axis. Alveolar expansion occurred in the caudal regions and alveolar contraction occurred in the cephalic regions, accordingly, the net alveolar volume of the entire lung was not altered significantly. Functional residual capacity was unchanged by prone positioning.

CONCLUSION: In ALI, prone positioning induced a more uniform distribution of gas and tissue along the cephalocaudal axis by reducing the cephalocaudal inflation gradient.

Abbreviations:
CT = Computed tomography
ALI = acute lung injury
FRC = functional residual capacity
HU = Hounsfield units
V/Q = ventilation-perfusion

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