British Journal of Anaesthesia, 2003, Vol. 91, No. 5 699-708
© 2003 The Board of Management and Trustees of the British Journal of Anaesthesia
Laboratory Investigations |
Lung density distribution in dynamic CT correlates with oxygenation in ventilated pigs with lavage ARDS
Departments of 1 Anaesthesiology and 2 Radiology, Johannes Gutenberg-University, School of Medicine, Langenbeckstrasse 1, D-55131 Mainz, Germany. 3 Department of Anesthesia, University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, USA 4 Present address: Veteran’s Administration Medical Center, Los Angeles, University of California, 11301 Wilshire Boulevard, Los Angeles, CA 90070, USA
Corresponding author. E-mail: klm@mail.uni-mainz.de 
This study contains parts of the doctoral thesis of Elena Ribel.
Background. Fast dynamic computed tomography (dCT) has been used to assess regional dynamics of lung inflation and deflation processes. The aim of this study was to relate ventilation-induced changes in lung density distribution, as measured over several respiratory cycles by dCT, to oxygenation and shunt fraction in a lavage acute respiratory distress syndrome model.
Methods. Six anaesthetized pigs underwent pressure-constant ventilation (FIO2=1.0, inspiratory:expiratory ratio=1:1) before and after induction of lung damage by saline lavage. Mean airway pressure (P
) was varied (8, 13, 18, 23, 28, 33, and 38 cm H2O) in random order. At each P level, dCT acquisitions were performed over several respiratory cycles (Somatom Plus4, Siemens; supradiaphragmatic transverse slice; thickness=1 mm; temporal resolution=100 ms). During scanning at each P, arterial and mixed venous blood were obtained for blood gas analysis and shunt calculation. In each CT image, fractional areas (FA) of defined density ranges representing ventilated lung and atelectasis were determined by planimetry using dedicated software. The FA data of individual 100 ms scans were averaged over several respiratory cycles, and expressed as mean FA in percentage of total lung area at each P. For atelectatic lung parenchyma a quantitative relationship of the respective mean FA to shunt fraction was studied using regression analysis.
Results. Under steady-state conditions, mean FA of atelectasis correlated linearly with the calculated shunt fraction (healthy lungs, r=+0.76; lavaged lungs, r=+0.89). There is a non-linear relationship between mean FA of ventilated lung parenchyma and mean FA of atelectasis with PaO2.
Conclusions. We conclude that dCT allows assessment of the effects of ventilator adjustments and resultant P; changes upon lung aeration and oxygenation rapidly, and with good spatial and temporal resolution. This may benefit patients with acute lung injury, whose ventilatory pattern may be optimized as early as during their first diagnostic workup.
Br J Anaesth 2003; 91: 699–708
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