title: Diagnostic value of abdominal free air detection on a plain chest radiograph in the early postoperative period: a prospective study in 648 consecutive patients who have undergone abdominal surgery.
abstract: BACKGROUND
  To the best of our knowledge, this is the first study to evaluate the predictive value of free air (on a plain radiograph) for bowel perforation in a large prospective cohort of surgical patients.
  
  
  METHODS
  All consecutive patients undergoing abdominal surgery between January 2011 and June 2012 were screened for this study. We performed an upright chest radiograph on the second and third postoperative day. Thereafter, additional radiographic evaluations were performed every 2 days until the disappearance of abdominal free air.
  
  
  RESULTS
  Of the 648 subjects enrolled in our study, free abdominal air was found in 65 subjects on the first radiographic evaluation (2 days after surgery), 51 on the second (3 days after surgery), three on the third (5 days after surgery), and none on the fourth (7 days after surgery). The presence of free abdominal air was associated with an increased risk of gastrointestinal perforation. The presence of free air was associated with a hazard ratio (HR) of 21.54 (95% CI 9.66-48.01, p<0.001) and a HR of 23.87 (95% CI 10.68-53.34, p<0.001) at 2 and 3 days after surgery, respectively. Sensitivity, specificity, positive predictive value, and negative predictive value were 70, 93, 33, and 98%, respectively, at 2 days after surgery, and similar results were confirmed at 3 days after surgery.
  
  
  CONCLUSIONS
  We believe that the presence of free air at 3 days after surgery should not be considered a common finding. Here, we demonstrate that the detection of free air has a remarkable predictive value for gastrointestinal perforation, which has been overestimated in previous experience.
authors.affiliation: University Federico II of Naples, Naples, Italy. milone.marco@alice.it
authors.forename: Marco
authors.initials: M
authors.lastname: Milone
authors.forename: Matteo Nicola Dario
authors.initials: MN
authors.lastname: Di Minno
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Bifulco
authors.forename: Paola
authors.initials: P
authors.lastname: Maietta
authors.forename: Loredana Maria
authors.initials: LM
authors.lastname: Sosa Fernandez
authors.forename: Mario
authors.initials: M
authors.lastname: Musella
authors.forename: Vittorio
authors.initials: V
authors.lastname: Iaccarino
authors.forename: Claudio
authors.initials: C
authors.lastname: Buccelli
authors.forename: Carmine
authors.initials: C
authors.lastname: Nappi
authors.forename: Francesco
authors.initials: F
authors.lastname: Milone
mesh_terms: D000005:Abdomen / Q000601:surgery*; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D015994:Incidence; D007416:Intestinal Perforation / Q000000981:diagnostic imaging* / Q000453:epidemiology / Q000209:etiology; D008297:Male; D008875:Middle Aged; D011027:Pneumoperitoneum / Q000000981:diagnostic imaging* / Q000453:epidemiology / Q000209:etiology; D011183:Postoperative Complications / Q000000981:diagnostic imaging* / Q000453:epidemiology; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011859:Radiography; D012680:Sensitivity and Specificity