Received: 5 July 2022 | Revised: 4 September 2022 | Accepted: 20 September 2022 DOI: 10.1111/nmo.14485 ORIGINAL ARTICLE Evaluation of abdominal gas by plain abdominal radiographs Elizabeth Barba1,2 | Dan M. Livovsky1 | Lucia Relea3 | Luis G. Alcalá-­Gonzalez1 | Sergio Quiroga4 | Anna Accarino1 | Fernando Azpiroz1 1 Digestive System Research Unit, University Hospital Vall d'Hebron; Centro Abstract de Investigación Biomédica en Red de Background: Our aim was to determine the reliability of plain abdominal radiographs Enfermedades Hepáticas y Digestivas (Ciberehd); Universitat Autònoma de for the evaluation of abdominal gas content in patients with functional digestive Barcelona, Bellaterra, Spain symptoms. 2 Gastroenterology Department, Hospital Clínic de Barcelona, Bellaterra, Spain Methods: Abdominal CT scan scout views, mimicking a conventional plain abdominal 3 Gastroenterology Department, Hospital radiograph, were obtained from 30 patients both during episodes of abdominal dis- Universitario Puerta de Hierro, Madrid, tension and basal conditions. Physicians (n = 50) were instructed to rate the estimated Spain 4 volume of gas in the 60 images presented in random sequence using a scale graded Radiology Department, University Hospital Vall d'Hebron, Barcelona, Spain from 0 to ≥600 ml. Key Results: The gas volumes estimated in the scout views differed from those meas- Correspondence Dan M. Livovsky, Digestive Diseases ured by CT by a median of 90 (95% CI 70–­102) ml, and the misestimation was not Institute, Shaare Zedek Medical Center, related to the absolute volume in the image. The accuracy of the observers, meas- and Faculty of Medicine, Hebrew University of Jerusalem, Shmu'el Bait St ured by their mean misestimation, was not related to their specialty or the training 12, Jerusalem 9103102, Israel. status (misestimation by 96 (95% CI 85–­104) ml in staff vs 78 (70–­106) ml in resi- Email: danlivo@szmc.org.il dents; p = 0.297). The accuracy was independent of the order of presentation of Present address the images. Gas volume measured by CT in the images obtained during episodes of Dan M. Livovsky, Digestive Diseases Institute, Shaare Zedek Medical Center, abdominal distension differed by a median of 39 (95% CI 29–­66) ml from those dur- and Faculty of Medicine, Hebrew ing basal conditions, and this difference was misestimated by a median of 107 (95% University of Jerusalem, Jerusalem, Israel CI 94–­119) ml. The accuracy of these estimations was not related to the absolute gas Funding information volumes (R = −0.352; p < 0.001) or the magnitude of the differences. This work was supported in part by the Spanish Ministry of Economy and Conclusions & Inferences: Plain abdominal radiographs have limited value for the Competitiveness (Dirección General de evaluation of abdominal gas volume in patients with functional gut disorders. Investigación Científica y Técnica, SAF 2016-­76648-­R); Ciberehd is funded by the Instituto de Salud Carlos III. Dan KEYWORDS M. Livovsky received support from the abdominal CT imaging, abdominal distension, abdominal radiographs, intestinal gas Israeli Medical Association and from Israel Gastroenterological Association 2020 fellowship grants. Elizabeth Barba, Dan M. Livovsky Shared first authorship The work was conducted while at: Digestive System Research Unit Hospital General Vall d'Hebron 08035-­Barcelona, Spain This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. © 2022 The Authors. Neurogastroenterology & Motility published by John Wiley & Sons Ltd. Neurogastroenterology & Motility. 2023;35:e14485.  wileyonlinelibrary.com/journal/nmo | 1 of 7 https://doi.org/10.1111/nmo.14485 2 of 7 | BARBA et al. 1 | I NTRO D U C TI O N PRACTITIONER POINTS Patients with functional digestive symptoms, that is, without de- • The evaluation of patients with functional gut disorders tectable organic disorders, frequently attribute their symptoms to presenting with severe episodes of abdominal bloat- excess abdominal gas. Indeed, gas-­related symptoms, such as ab- ing and distension frequently includes plain abdominal dominal distension, bloating, flatulence, and borborygmi, affect a radiographs. large proportion of patients with functional gut disorders and con- • To determine the reliability of this practice, we com- stitute their most bothersome complaint1–­3. pared the objective values of abdominal gas, measured The clinical value of plain abdominal radiographs for the investi- by a validated CT technique in patients with functional gation of abdominal symptoms has been studied in the setting of the gut disorders, to the subjective estimation of gas vol- emergency department, and despite that its clinical value is not clear, umes on plain AP projection of the same CT images plain abdominal radiographs remain one of the most common radio- 4–­8 (scout views) by a cohort of physicians. logical examinations performed in this setting ; indeed, a study from • The volumes of abdominal gas were grossly misesti- Switzerland reported that only 12% of plain abdominal radiographs mated in the scout views, indicating that plain abdominal performed in 1997 patients (2.2% of all patients admitted to the ER) radiographs have no value for the evaluation of intesti- were actually indicated9. Correspondingly, an Italian study showed nal gas volume in patients with functional gut disorders. that plain abdominal radiographs were used in 38% of patients pre- senting with acute abdominal pain; the sensitivity for detecting acute disease was 28%5. Likewise, plain abdominal radiographs were per- formed in 42% of patients presenting to the ER with constipation, and abdominal distension were evaluated. After obtaining written in- the findings had no significant effect on management7. formed consent, patients were instructed to come to the labora- In particular, the evaluation of patients with severe episodes of tory under two different conditions: when they felt minimal or no abdominal bloating and distension frequently includes plain abdom- abdominal distension (basal conditions) and during an episode of inal radiographs; based on the subjective interpretation of the im- visible distension. On each occasion, abdominal CT scans were ob- ages, the symptoms in some patients are categorically attributed to tained with a helical multi-­slice CT scanner (exposure 120 kV and excess of gas in the gut and are followed by sometimes drastic rec- 50 mA), using the available dose reduction options (tube current ommendations to reduce intestinal gas production. However, some modulation). Images were obtained in the supine position during studies objectively measuring intestinal gas content by means of a single breath hold. No oral or intravenous contrast medium was abdominal CT in patients with functional gut disorders consistently administered. Measurement of the volume of abdominal gas in 10–­14 found gas volumes within the normal range . To address this dis- the CT images was performed by means of an original software crepancy, our aim was to determine the reliability of plain abdominal program specifically developed in our laboratory and previously radiographs for the evaluation of abdominal gas content in patients described in detail15,16 . A database of 104 patients was collected. with functional gas-­related symptoms. To this aim, we analyzed CT The results from the original studies have been published else- images obtained in previous studies in patients with functional gut where 17,18 . disorders complaining of abdominal distension and compared the objective values of abdominal gas measured by CT to the subjective estimation of gas volumes from a plain AP projection of the same CT 2.3 | Current analysis: estimation of gas volumes images by a cohort of physicians. on CT scouts 2.3.1 | Material 2 | M ATE R I A L & M E TH O DS For the present study, CT scout views, that is, antero-­posterior 2.1 | Study design projections mimicking a conventional plain abdominal radio- graph (Figure 1), were obtained from a representative selection Prospective analysis of images obtained in previous studies (Clinc​ of 30 patients in the database19; 16 fulfilled Rome III criteria for ialTr​ials.gov: NCT01205100). constipation-­predominant irritable bowel syndrome (IBS-­C) and 14 for functional bloating/distension. A sequence of 60 images in random order (30 corresponding to distension episodes and 30 to 2.2 | Database: collection and analysis of basal conditions in the same patients) was prepared, and another CT images sequence was obtained by reversing the order of the first sequence. All images contained between 20 ml y 600 ml gas: 51 images in the In previous studies, patients with disorders of gastrointestinal 20–­200 ml range represented the most common values observed in function (by Rome III criteria) complaining of episodes of visible patients with functional gut disorders; 7 images in the 250–­450 ml BARBA et al. | 3 of 7 TA B L E 1 Demographics of participants Specialty (n) GE (20) IM (11) RX (11) GS (6) Sex, F/M 11/9 5/6 4/7 2/4 Staff/residents 15/5 7/4 8/3 4/2 * Experience, years 6 (3–­3 4) 6(2–­9) 8 (3–­3 4) 7 (3–­11) Institution, VH/HC/HP 7/4/9 3/4/4 4/4/3 2/4/0 Abbreviations: GE, Gastroenterology; GS, General Surgery; HC, Hospital Clinic, Barcelona, Spain; HP, Hospital de la Princesa, Madrid, Spain; IM, Internal Medicine; RX, Radiology; VH, Vall d'Hebron University Hospital, Barcelona, Spain. *Years from MD degree, median (range). procedure, each participant underwent a brief standardized train- ing, being exposed to a training set of images labeled with their real volume of gas: 3 images in the lower 50 ml range (containing 29 ml, 33 ml, and 34 ml gas, respectively) and another 3 images in the upper 500 ml range (containing 583 ml, 531 ml, and 492 ml gas, respectively). 2.4 | Statistical analysis Volumes of gas estimated by the participants were compared to the volumes measured by the CT analysis program, taken as reference, and the differences (misestimation) were calculated, as an index of the accuracy of the observations. The median or grand median (95% CI) of the variables measured was calculated. The Kolmogorov-­ Smirnov test was used to check the normality of the data distri- bution. Parametric normally distributed data were compared by F I G U R E 1 Examples of abdominal CT scans and scout views as Student's t-­test for unpaired data or ANOVA (for more than 2 vari- plain AP projections in two patients. Images contain 70 ml (A) and, (360 ml gas measured by volumetric analysis, respectively ables); otherwise, the Mann-­Whitney U test or the Kruskal-­Wallis test (for more than 2 variables) was used. In order to evaluate the range represented the very top values seen in these patients17,18; 2 role of experience, the absolute misestimation value per partici- images in the 600 ml range were included in search for the detection pant (mean value of the 60 images) was correlated with the years in threshold. practice. Pearson's correlation coefficient (Pearson's r’) was used to examine correlations between parametric normally distributed data and Spearman's r’ for non-­parametric data. 2.3.2 | Participants Fifty physicians from 3 academic institutions in Spain (University 3 | R E S U LT S Hospital Vall d'Hebron, Barcelona; Hospital Clinic, Barcelona; Hospital de la Princesa, Madrid) accepted to participate in the study. Participants 3.1 | Demographics were recruited among four specialties: Gastroenterology (n = 20), Internal Medicine (n = 12), Radiology (n = 12), and General Surgery Two participants (1 internist and 1 radiologist) did not complete the (n = 6), including staff physicians (n = 34) and residents (n = 14). study, and data from 48 participants, representing Gastroenterology (n = 20), Internal Medicine (n = 11), Radiology (n = 11) and General Surgery (n = 6), were included for analysis (Table 1). 2.3.3 | Procedure Each participant was randomly allocated to evaluate one of the se- 3.2 | Estimation of gas volumes quences containing the 60 images. Participants were instructed to rate the estimated volume of gas in each image using a scale graded The estimated values of gas volumes on plain AP projections showed from 0 ml to ≥600 ml with 50 ml divisions. Before the evaluation a great dispersion as compared to the real values measured by CT 4 of 7 | BARBA et al. F I G U R E 2 Abdominal gas volume. Relation between objective gas volumes measured by CT and estimated volumes on plain AP projections. Individual data of 48 observers for 60 images are shown. Note, great overlap of estimated values, even with largest gas volumes F I G U R E 3 Accuracy of estimated volumes on plain AP projections. Relation between absolute values of misestimation (absolute difference from volume measured by CT) and volumes measured by CT. Individual data of 48 observers for 60 images are shown. Note, similar error regardless of the real gas volume (Figure 2). The misestimation, measured as difference between esti- and 87 (55–­102) ml by radiologists; p = 0.322), training status (mises- mated and real values, was not related to the absolute gas volume in timation by 96 (85–­104) ml in staff versus 78 (70–­106) ml in residents; the image (R = −0.245; p < 0.001); that is, the error was similar with p = 0.297) (Figure 5), or years of experience (R = 0.073; p = 0.618). small and large volumes (Figure 3). However, small volumes tended The accuracy of the observations was independent of the order of to be overestimated and large volumes underestimated, partly be- presentation of the images (R = −0.111; p < 0.001; Figure S1). No dif- cause of the saturation effect of the lower and upper limits of the ferences in accuracy were observed between the two randomization scale (Figure 4). sequences presented (misestimation by 75 (62–­87) ml and 62 (52–­ 73) ml, respectively; p = 0.107). 3.3 | Role of training, experience, and previous exposure 3.4 | Differences between paired observations (basal versus distension) The accuracy of individual participants, determined by averaging the values of the misestimation in all his/her observations, was not re- Gas volume measured by CT in the images obtained in the same lated to the specialty (misestimation by 106 (79–­133) ml in surgeons, patients during episodes of abdominal distension differed by 39 92 (67–­111) ml in gastroenterologists, 86 (64–­126) ml in internists (29–­66) ml from those during basal conditions, and this difference BARBA et al. | 5 of 7 F I G U R E 4 Over and underestimations on plain AP projections. Relation between misestimations (difference from volume measured by CT) and volumes measured by CT. Individual data of 48 observers for 60 images are shown. Note, overestimation of smaller volumes and underestimation of larger volumes was misestimated by 107 (94–­119) ml in the plain AP projections; in 38% of the cases with an increase detected by CT during distension episodes, the estimated volume was smaller; in 40% of the cases with a decrease detected by CT, the estimated volume was greater (Figure 6). The accuracy of these estimations was neither related to the absolute gas volumes (R = −0.352; p < 0.001) nor to the magni- tude of the differences (Figure 6). 4 | DISCUSSION Our data indicate that plain abdominal radiographs have limited value for the evaluation of abdominal gas volume, specifically in patients with functional digestive symptoms and gas volumes within the 600 ml range. The estimations in different subjects were poor, but also when comparing images taken in the same subjects on different occasions, the estimations failed to recog- nize whether the volume was larger or not. The limitation of the technique cannot be overcome by training, and the same accuracy, measured as misestimation, was observed regardless of specialty (specialized radiologists versus gastroenterologists, internists or general surgeons), and training status (specialized staff physicians F I G U R E 5 Individual accuracy in gas content estimations. For versus residents). Furthermore, the accuracy did not improve or each observer (n = 48; x-­axis) figure shows absolute misestimation deteriorate with repeat estimations, showing neither learning nor value (mean value of the 60 images; y-­axis) fatigue trends. The accuracy of the estimated volumes was tested against ob- Gas in the gut by-­and-­large derives from the fermentation by co- jective measurements of gas by CT analysis. A standard technique lonic microbiota of food residues that are not absorbed in the small was used in the acquisition for abdominal CT imaging, and gas bowel. Intraluminal gas content is kept within 100–­200 ml by a tight volumes were measured using a software program previously homeostatic control: the volume produced is disposed of by 3 routes: developed in our laboratory. The program has been previously (a) gas-­consuming microorganisms, (b) absorption and clearance by validated by a thorough series of studies comparing gas volumes breath, and (c) anal evacuation20,21. Despite that gas-­related symptoms before and after infusion of known gas loads into the intestine. are commonly attributed to excess intestinal gas, gas volumes mea- Detailed description and validation of the program has been sured by CT have been consistently found within the normal range, published 15. even during episodes of visible abdominal distension 10–­14. Some data 6 of 7 | BARBA et al. F I G U R E 6 Differences in gas volumes between images obtained during basal conditions and distension. Relation between objective gas differences measured by CT (x-­axis) and estimated differences on plain AP projections (y-­ axis). Individual data of 48 observers for 30 paired images are shown indicate that the symptoms in these patients are due to a sensitive gut Our data may have inference in clinical practice, suggesting with poor tolerance of contents, and visible abdominal distension is that plain abdominal radiographs to evaluate intestinal gas could due to abdomino-­phrenic dyssynergia (diaphragmatic push and down- be spared, because the technique is not reliable for that purpose; wards displacement of contents). In a recent study, we reviewed the moreover, the possibility of excess gas is very unlikely in patients whole pool of 104 consecutive patients with paired abdominal CT im- with reliable diagnosis of a functional gut disorder, and doubtful ages obtained during basal conditions and episodes of distension in our cases may rather undergo more precise imaging techniques, that laboratory: in most patients, the difference in gas between both con- provide quantitative measures of gas, and a more precise exam of ditions was within the ±300 ml range, as in the images evaluated in the abdominal structures. present study; in only a minority (5 out of 104 patients), distention was associated with an increase in gas above that range, and even these AU T H O R C O N T R I B U T I O N S patients exhibited a clear pattern of abdomino-­phrenic dyssynergia22. EB. Study design, conduction of studies, data analysis. DL. Conduction In a previous study, we specifically measured the volume of rec- of studies, data analysis. LR. Study design, conduction of studies, data tal gas in patients with functional digestive disorders and found no analysis. SQ. Analysis of CT images. LA. Conduction of studies. AA. significant differences compared to healthy subjects, either during Study design. FA. Study design, data interpretation, manuscript prep- basal conditions or during a distension episode23. By contrast, an aration. All authors approved the final draft of the manuscript. interesting study measured gas volumes in the rectum by CT imaging in a large pool of patients presenting with constipation (n = 141); the AC K N OW L E D G M E N T S volume of rectal gas was found significantly higher in patients with The authors thank Gloria Santaliestra for secretarial assistance. functional outlet obstruction compared to patients with slow transit or normal transit constipation24. F U N D I N G I N FO R M AT I O N Limitations of plain abdominal radiographs for the evaluation of This work was supported in part by the Spanish Ministry of Economy intestinal gas content were also encountered by previous studies. and Competitiveness (Dirección General de Investigación Científica Some differences between patients and healthy controls or between y Técnica, grant SAF 2016-­76,648-­R to F Azpiroz); Ciberehd is patients with and without distension were reported, but no correla- funded by the Instituto de Salud Carlos III. Dan M. Livovsky re- tions between gas content and symptoms were found. Furthermore, ceived support from the Israeli Medical Association and from Israeli it was also reported that changes in body position introduced a Gastroenterological Association 2020 fellowship grants. large variability in the estimations (67% increase from upright to su- pine)25–­27. Other studies also failed to detect associations between C O N FL I C T O F I N T E R E S T S estimated gas contents and gas-­related symptoms during provoca- the authors declare no conflict of interest. tive tests 11,28. Our data in relation to gas detection apply specifically to patients ORCID with functional digestive disorders with gas volumes below 600 ml, Elizabeth Barba https://orcid.org/0000-0002-5986-6592 but we wish to acknowledge that in patients with organic disorders, Dan M. Livovsky https://orcid.org/0000-0002-8212-9638 such as intestinal dysmotility and pseudo-­obstruction, massive gas Lucia Relea https://orcid.org/0000-0002-3673-5346 retention may be reliably identified in plain abdominal radiographs 29. Luis G. Alcalá-­Gonzalez https://orcid.org/0000-0003-3247-1539 BARBA et al. | 7 of 7 Sergio Quiroga https://orcid.org/0000-0001-8671-7616 17. Barba E, Accarino A, Azpiroz F. 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