title: Occult pneumothorax in trauma patients: should this be sought in the focused assessment with sonography for trauma examination?
abstract: OBJECTIVE
  At present, CT scan is the gold standard for detecting occult traumatic pneumothorax not apparent on supine chest X-ray radiograph. Recently there were suggestions to expand focused assessment with sonography for trauma (FAST) to include thoracic ultrasound for detecting pneumothorax. The aim of the present study is to determine the incidence of occult pneumothorax (as shown by CT) in the subgroup of trauma patients undergoing FAST.
  
  
  METHODS
  Review of all trauma patients with FAST done from 1 June 2001 to 31 October 2002. Incidence of occult pneumothorax as diagnosed by CT was determined. Patients were not counted as having true occult pneumothorax if they had chest drains inserted before arrival or imaging studies. Selected clinical findings were tested for association with occult pneumothorax.
  
  
  RESULTS
  In total, 143 patients underwent FAST, of whom 137 (95.8%) had chest X-ray examination performed. Of the 137 patients 59 required CT abdomen and/or thorax. Occult pneumothorax was found in three patients (2.1%). A history of thorax and/or abdominal injury plus one or more of: (i) mechanisms potentially causing major trauma; (ii) abnormal chest examination; and (iii) chest X-ray radiograph abnormality in the absence of pneumothorax, was significantly associated with the presence of occult pneumothorax (P = 0.03, Fisher's exact test; sensitivity: 100%; specificity: 71%; likelihood ratio: 3.42).
  
  
  CONCLUSIONS
  The incidence of occult pneumothorax in the subgroup of trauma patients undergoing FAST is low. It implies that routine screening for its presence by adding thoracic ultrasound to FAST is unnecessary. Identifying those at risk of occult pneumothorax for further investigation appeared feasible.
authors.affiliation: Department of Accident and Emergency, Accident and Emergency Medicine Academic Unit, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong, China. tammk@ha.org.hk
authors.forename: Michael M K
authors.initials: MM
authors.lastname: Tam
mesh_terms: D000007:Abdominal Injuries / Q000000981:diagnostic imaging / Q000453:epidemiology; D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D015897:Comorbidity; D004635:Emergency Medicine / Q000379:methods*; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D010043:Outcome and Process Assessment, Health Care; D011030:Pneumothorax / Q000000981:diagnostic imaging* / Q000453:epidemiology; D011859:Radiography; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D017678:Sex Distribution; D013898:Thoracic Injuries / Q000000981:diagnostic imaging / Q000453:epidemiology; D014463:Ultrasonography; D014947:Wounds and Injuries / Q000000981:diagnostic imaging* / Q000453:epidemiology; D014949:Wounds, Nonpenetrating / Q000000981:diagnostic imaging / Q000453:epidemiology; D014950:Wounds, Penetrating / Q000000981:diagnostic imaging / Q000453:epidemiology