CT-Assessment of Dependent Lung Densities in Man during General Anaesthesia

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Abstract
Purpose: We aimed to describe the frequency of atelectasis occurring during anaesthesia, to describe the size and pattern of the atelectasis, and to standardise the method of identifying the atelectasis and calculate its area. Material and Methods: Patients (n=109) scheduled for elective abdominal surgery were examined with CT of the thorax during anaesthesia. Results: In 95 patients (87%) dependent pulmonary densities were seen, interpreted as atelectasis. Two different types of atelectasis were found — Homogeneous (78%) and non-homogeneous (9%). Attenuation values in histograms of the lung and atelectasis were studied using 2 methods of calculating the atelectatic area. Conclusion: On the basis of the present findings, we defined atelectasis as pulmonary dependent densities with attenuation values of —100 to +100 HU.