Aim: To compare the estimated size of spontaneous pneumothoraces using the established Rhea inter-pleural distances method with the CT-derived Collins method.
Method: Adult patients with spontaneous pneumothorax treated conservatively were identified from the ED databases. X-rays were reviewed independently by two researchers and measured according to the methods described by Rhea and Collins. Estimates of size derived by the two methods were compared using bias plot analysis techniques.
Results: A total of 156 X-rays in 57 patients were identified. A total of 82% were male with a median age of 22 years. Pneumothoraces varied in size from 4% to 88%. The average difference between methods was 4% (Collins method estimating larger size) with 95% limits of agreement -3.8% to 11.7%. Agreement was very close for small pneumothoraces but deteriorated with increasing pneumothorax size (Collins methods estimated larger pneumothorax size).
Conclusion: The Rhea method for estimating pneumothorax size is acceptably accurate for smaller pneumothoraces but may significantly under-estimate the size of larger pneumothoraces.