title: Estimating the rate of re-expansion of spontaneous pneumothorax by a formula derived from computed tomography volumetry studies.
abstract: BACKGROUND
  Available evidence suggesting that the rate of re-expansion of spontaneous pneumothorax is 1.25%/day is based on a small sample and mathematical modelling-based estimates.
  
  
  OBJECTIVE
  To estimate the rate of re-expansion of spontaneous pneumothoraces by a formula derived from computed tomography volumetry studies.
  
  
  METHODS
  This retrospective study included adult patients with spontaneous pneumothorax, identified from patient management databases, who were treated conservatively. Medical records were reviewed to confirm that no intervention such as aspiration or catheter drainage had occurred. Radiographs were reviewed independently by two researchers and measured according to the method described by Collins et al. Their formula was used to estimate pneumothorax size on each date. The rate of re-expansion was defined as the change in size (%)/number of days between radiographs. Patients were excluded if they did not have at least two radiographs taken, at least 1 day apart. Data were analysed using cluster analysis by patient to minimise the effect of repeated measures from an individual patient.
  
  
  RESULTS
  88 episodes were identified in 57 patients. 82% were men and the patients had a median age of 22 years. The average rate of re-expansion was 2.2%/day (95% confidence interval 1.4% to 3.0%), but varied between -7.5% and 13.4%/day.
  
  
  CONCLUSIONS
  Spontaneous pneumothoraces treated conservatively re-expand at an average rate of 2.2%/day.
authors.affiliation: Joseph Epstein Centre for Emergency Medicine Research, Western Health and University of Melbourne, Melbourne, Victoria, Australia. Anne-Maree.Kelly@wh.org.au
authors.forename: A-M
authors.initials: AM
authors.lastname: Kelly
authors.forename: J
authors.initials: J
authors.lastname: Loy
authors.forename: A Y L
authors.initials: AY
authors.lastname: Tsang
authors.forename: C A
authors.initials: CA
authors.lastname: Graham
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008954:Models, Biological; D015588:Observer Variation; D011030:Pneumothorax / Q000000981:diagnostic imaging / Q000473:pathology*; D011379:Prognosis; D012075:Remission, Spontaneous; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed