Abstract
BackgroundPneumoperitoneum is a rare cause of abdominal pain characterized by a high mortality. Ultrasonography (US) can detect free intraperitoneal air; however, its accuracy remains unclear. The aims of this pilot study were to define the diagnostic performance and the reliability of abdominal US for the diagnosis of pneumoperitoneum.MethodsThis was a prospective observational study. Four senior and two junior physicians were shown, in an unpaired randomized order, abdominal US videos from 11 patients with and 11 patients without pneumoperitoneum. Abdominal US videos were obtained from consecutive patients presenting to ED complaining abdominal pain with the diagnosis of pneumoperitoneum established by CT. Abdominal US was performed according to a standardized protocol that included the following scans: epigastrium, right and left hypochondrium, umbilical area and right hypochondrium with the patient lying on the left flank. We evaluated accuracy, intra- and inter-observer agreement of abdominal US when reviewed by senior physicians. Furthermore, we compared the accuracy of a “2 scan-fast exam” (epigastrium and right hypochondrium) vs the full US examination and the accuracy of physicians expert in US vs nonexpert ones. Finally, accuracy of US was compared with abdominal radiography in patients with available images.ResultsConsidering senior revision, accuracy of abdominal US was 88.6 % (95 % CI 79.4-92.4 %) with a sensitivity of 95.5 % (95 % CI 86.3–99.2 %) and a specificity of 81.8 % (95 % CI 72.6–85.5 %). Inter- and intra-observer agreement (k) were 0.64 and 0.95, respectively. Accuracy of a “2 scan-fast exam” (87.5 %, 95 % CI 77.9–92.4 %) was similar to global exam. Sensitivity of abdominal radiography (72.2 %, 95 % CI 54.8–85.7 %) was lower than that of abdominal US, while specificity (92.5 %, 95 % CI 79.5–98.3 %) was higher. Accuracy (68.2 %, 95 % CI 51.4–80.9 %) of junior reviewers evaluating US was lower than senior reviewers.ConclusionsSenior physicians can recognize US signs of pneumoperitoneum with a good accuracy and reliability; sensitivity of US could be superior to abdominal radiography and a 2 fast-scan exam seems as accurate as full abdominal examination. US could be a useful bedside screening test for pneumoperitoneum.Trial registry ClinicalTrials.gov; No.: NCT02004925; URL: http://www.clinicaltrials.govElectronic supplementary materialThe online version of this article (doi:10.1186/s13089-015-0032-6) contains supplementary material, which is available to authorized users.
Highlights
Pneumoperitoneum is a rare cause of abdominal pain characterized by a high mortality
Previous studies evaluated diagnostic performance of abdominal US to detect free intraperitoneal air demonstrating that US has a superior sensitivity to diagnose pneumoperitoneum compared with abdominal radiography with the most important sonographic findings including the enhancement of peritoneal stripe and reverberation with a ring down artifact starting from peritoneum [10–20]
Comparing abdominal US with abdominal radiography, we showed that radiographic signs of pneumoperitoneum are detected with less sensitivity than US signs (72 % vs 86 %) while specificity of radiography was higher even if statistical significance was not reached (92.5 % vs 80 %), showing that US and radiography can be used as complementary tests to increase accuracy
Summary
Pneumoperitoneum is a rare cause of abdominal pain characterized by a high mortality. Ultrasonography (US) can detect free intraperitoneal air; its accuracy remains unclear The aims of this pilot study were to define the diagnostic performance and the reliability of abdominal US for the diagnosis of pneumoperitoneum. Pneumoperitoneum most commonly results from a perforated hollow viscus It is a rare cause of acute abdominal pain representing less than 1 % of presentation to emergency department (ED) and its prompt diagnosis is paramount due to its high mortality. Previous studies evaluated diagnostic performance of abdominal US to detect free intraperitoneal air demonstrating that US has a superior sensitivity to diagnose pneumoperitoneum compared with abdominal radiography with the most important sonographic findings including the enhancement of peritoneal stripe and reverberation with a ring down artifact starting from peritoneum [10–20]. Free abdominal air produces a sonographic appearance of linear enhancement of peritoneal stripe with reverberation artifacts (Fig. 2a; Additional file 1), and the high differences in acoustic impedance between closely opposed air and fluid produce ring down artifacts starting from peritoneal line (Fig. 2b; Additional file 2)
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