EDITORIALS Current Approaches to Assessing the Degree of Airway Narrowing in Central Airway Obstruction Katarine V. L. Egressy and Septimiu D. Murgu Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Chicago, Chicago, Illinois
Accurate assessment of central airway obstruction (CAO) of various morphologic and mechanistic forms is an invaluable component of bronchoscopy practice. Reduction in airway lumen cross-sectional area (CSA), anatomic location, extent, morphologic features, and degree of dynamic narrowing affect decision-making and should be accurately described in bronchoscopy reports (1). Several techniques have been proposed for objective assessment of actual airway caliber or degree of airway narrowing (reported as percentage of normal). To date, however, no single “gold standard” technique is currently used in routine clinical practice. Current methods for objective quantification of CAO include several techniques that have various degrees of validity and reproducibility. Spirometry is not a reliable for quantifying the degree of CAO, and it does not identify the exact location, extent, or morphology of the airway narrowing. It also has low sensitivity for detecting mild to moderate reductions in airway caliber (2). Image-based quantification, such as multidetector computer tomography, with or without three-dimensional reconstruction, are dependent on respiratory cycle, anatomy, presence of secretions, and intra- and interobserver variability. It may also be difficult to perform in critically ill patients because of poor cooperation, especially with end-inspiration breath-holding maneuvers (3). Transcutaneous acoustic analysis techniques have been shown to have clinical use in follow-up of laryngotracheal stenosis; however, this technique underestimates the absolute lumen size when used for measurement of transverse cervical tracheal diameter (4). Radial
probe-balloon–based endobronchial ultrasound and optical coherence tomography have also been used, but they require bronchoscopy and additional technology that may not be readily available (5–7). Morphometric analysis of bronchoscopy images using cost-free image processing software has also been applied for assessing the percentage reduction in the airway CSA (8, 9). Indeed, from a flow dynamic standpoint, what matters most is the degree of narrowing based on percentage reduction in luminal CSA, and not the absolute airway diameter (10). Despite the availability of these objective techniques, practicing bronchoscopists continue to subjectively estimate the degree of airway narrowing. Subjective assessments, however, are inaccurate when they are based on visual estimation during bronchoscopy or simple still image analysis (9). Using the previously described stenosis and collapsibility indices is a practical and user-friendly alternative to measuring the absolute airway diameter (9). In fact, attempts to calculate the airway CSA are impractical for irregular airway morphologies, even for a known airway diameter. The study by Begnaud and colleagues in this month’s issue of AnnalsATS (pp. 85–90) analyzed current practices of quantifying CAO among members of American Association of Bronchology and Interventional Pulmonology (11). The study was performed by a survey-based method and hence suffers from potential recall and selection bias. One hundred eighteen survey responses were eventually analyzed. Each responder was asked to evaluate still bronchoscopic images of CAO and graded them on a numerical scale
of 0 to 100. Baseline calculations of the stenosis index were performed using Fuji software analysis, and CSA area was calculated in pixels by software measurement tools in the region of polygon selection. Previously described bronchoscopic image acquisition techniques were not used, and hence accuracy of initial measurement may have been compromised and potentially inadvertently resulted in a false baseline reference standard (8). Indeed, distance image distortion invariably affects the estimation of degree of CAO. This has been previously demonstrated and thoroughly described in published reviews of morphometric bronchoscopy. The responses of numerical analysis of CAO were compared with previously calculated baseline. Statistical analysis of the means was calculated on the basis of lesion type and previous experience. Opinions and practices from all responders were solicited in free text form and tabulated. Bronchoscopists either under- or overestimate the degree of stenosis when using still image analysis (9). Assessments of bronchoscopy videos may actually result in more accurate estimation of reduction in CSA, but this hypothesis has to be further studied. The study by Begnaud and colleagues supports the results from a previous study, in that there is no statistical correlation between the number of procedures performed and accurate subjective assessment of CAO (9). Most participants in this study agreed that an accurate and precise method should be used for quantification of CAO. Paradoxically, none of the participants surveyed reported use of quantitative
(Received in original form November 15, 2014; accepted in final form November 27, 2014 ) Correspondence and requests for reprints should be addressed to Septimiu D. Murgu, M.D., University of Chicago, 5841 S. Maryland Ave, MC6076, Chicago, IL 60637. E-mail: [email protected] Ann Am Thorac Soc Vol 12, No 1, pp 109–110, Jan 2015 Copyright © 2015 by the American Thoracic Society DOI: 10.1513/AnnalsATS.201411-523ED Internet address: www.atsjournals.org
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EDITORIALS or semiquantitative techniques of morphometric bronchoscopy for CAO measurements. No descriptive responses were given as to why quantitative measures were not being used in clinical practice. The study by Begnaud and colleagues also highlights the fact that in the era of evidence-based medicine and electronic medical records in which accurate data acquisition and processing may directly correlate with treatment decisions and outcomes, we still rely on guesswork or “experience” to assess the degree of CAO. As shown in previous studies, subjective estimates do not measure up to objective quantitative assessments such as morphometric bronchoscopy. The authors conclude by stating that precise and easy-to-use assessment tools for CAO are needed. In this regard, morphometric bronchoscopy aims to reduce the need for subjective estimates and error. However, most likely because of a delay of “real time” assessment and postprocedural time spent
on image analysis and quantification, this technique is not a widely used modality, as evident from the study by Begnaud and colleagues. In addition, noninvasive and physiological assessment tools for airway obstruction may be more valuable to the practicing bronchoscopists. Lateral airway pressure difference, as measured by a double lumen catheter, closely correlates with the critical CAO site identification and guides decisions regarding stent insertion at the flow-limiting segments (12). Noninvasive techniques may also play a pivotal role in correctly identifying the location of CAO and providing objective assessments after interventions (13). The future of morphometric bronchoscopy will likely consist of an integrated, automated, real-time modality that would be capable of obtaining accurate measurements of the airway lumen at the regions of interest. Novel bronchoscopes with two independent lenses at the tip of the device have been proposed (i.e., stereovision
References 1 Myer CM III, O’Connor DM, Cotton RT. Proposed grading system for subglottic stenosis based on endotracheal tube sizes. Ann Otol Rhinol Laryngol 1994;103:319–323. 2 Miller RD, Hyatt RE. Evaluation of obstructing lesions of the trachea and larynx by flow-volume loops. Am Rev Respir Dis 1973;108:475–481. 3 Polverosi R, Vigo M, Baron S, Rossi G. Evaluation of tracheobronchial lesions with spiral CT: comparison between virtual endoscopy and bronchoscopy [in Italian]. Radiol Med (Torino) 2001;102:313–319. 4 Husein M, Manoukian JJ, Platt R, Patenaude Y, Drouin S, Giguere ` C. Ultrasonography and videobronchoscopy to assess the subglottic diameter in the paediatric population: a first look. J Otolaryngol 2002; 31:220–226. 5 Nobuyama S, Kurimoto N, Matsuoka S, Inoue T, Shirakawa T, Mineshita M, Miyazawa T. Airway measurements in tracheobronchial stenosis using endobronchial ultrasonography during stenting. J Bronchology Interv Pulmonol 2011;18:128–132. 6 Murgu SD. Optical coherence tomography of the airways. Curr Respir Care Rep 2014;3:13–18. 7 Shirakawa T, Imamura F, Hamamoto J, Shirkakusa T. A case of successful airway stent placement guided by endobronchial ultrasonography. J Bronchology Interv Pulmonol 2004;11:45–48.
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bronchoscopy), which allow measurement of airway size, using the principle of triangulation, and correlate with computed tomography measurements (14). To date, however, no real-time data acquisition and processing systems are commercially available for measuring airway diameters or CSA (14). Image processing, complex calibration, and distortion image correction could be standardized, and image acquisition will remain the only operatordependent variable. This can be easily achieved, however, by properly controlling the bronchoscope during the procedure. In addition, a closer collaboration between parties involved (i.e., manufacturers, technical engineers, and bronchoscopists) may be helpful in designing bronchoscopes that fulfill the characteristics required for an objective, easy-to-use modality that eliminates guesswork all together. n Author disclosures are available with the text of this article at www.atsjournals.org.
8 Murgu S, Colt HG. Morphometric bronchoscopy in adults with central airway obstruction: case illustrations and review of the literature. Laryngoscope 2009;119:1318–1324. 9 Murgu S, Colt H. Subjective assessment using still bronchoscopic images misclassifies airway narrowing in laryngotracheal stenosis. Interact Cardiovasc Thorac Surg 2013;16:655–660. 10 Elliott EA, Dawson SV. Test of wave-speed theory of flow limitation in elastic tubes. J Appl Physiol 1977;43:516–522. 11 Begnaud A, Connett JE, Harwood EM, Jantz MA, Mehta, HJ. Measuring central airway obstruction: what do bronchoscopists do? Ann Am Thorac Soc 2015;12:85–90. 12 Nishine H, Hiramoto T, Kida H, Matsuoka S, Mineshita M, Kurimoto N, Miyazawa T. Assessing the site of maximal obstruction in the trachea using lateral pressure measurement during bronchoscopy. Am J Respir Crit Care Med 2012;185:24–33. 13 Handa H, Huang J, Murgu SD, Mineshita M, Kurimoto N, Colt HG, Miyazawa T. Assessment of central airway obstruction using impulse oscillometry before and after interventional bronchoscopy. Respir Care 2014;59:231–240. 14 Hayashi A, Takanashi S, Tsushima T, Denpoya J, Okumura K, Hirota K. New method for quantitative assessment of airway calibre using a stereovision fibreoptic bronchoscope. Br J Anaesth 2012;108: 512–516.
AnnalsATS Volume 12 Number 1 | January 2015
Accurate assessment of central airway obstruction (CAO) of various morphologic and mechanistic forms is an invaluable component of bronchoscopy practice. Reduction in airway lumen cross-sectional area (CSA), anatomic location, extent, morphologic features, and degree of dynamic narrowing affect decision-making and should be accurately described in bronchoscopy reports (1). Several techniques have been proposed for objective assessment of actual airway caliber or degree of airway narrowing (reported as percentage of normal). To date, however, no single “gold standard” technique is currently used in routine clinical practice. Current methods for objective quantification of CAO include several techniques that have various degrees of validity and reproducibility. Spirometry is not a reliable for quantifying the degree of CAO, and it does not identify the exact location, extent, or morphology of the airway narrowing. It also has low sensitivity for detecting mild to moderate reductions in airway caliber (2). Image-based quantification, such as multidetector computer tomography, with or without three-dimensional reconstruction, are dependent on respiratory cycle, anatomy, presence of secretions, and intra- and interobserver variability. It may also be difficult to perform in critically ill patients because of poor cooperation, especially with end-inspiration breath-holding maneuvers (3). Transcutaneous acoustic analysis techniques have been shown to have clinical use in follow-up of laryngotracheal stenosis; however, this technique underestimates the absolute lumen size when used for measurement of transverse cervical tracheal diameter (4). Radial
probe-balloon–based endobronchial ultrasound and optical coherence tomography have also been used, but they require bronchoscopy and additional technology that may not be readily available (5–7). Morphometric analysis of bronchoscopy images using cost-free image processing software has also been applied for assessing the percentage reduction in the airway CSA (8, 9). Indeed, from a flow dynamic standpoint, what matters most is the degree of narrowing based on percentage reduction in luminal CSA, and not the absolute airway diameter (10). Despite the availability of these objective techniques, practicing bronchoscopists continue to subjectively estimate the degree of airway narrowing. Subjective assessments, however, are inaccurate when they are based on visual estimation during bronchoscopy or simple still image analysis (9). Using the previously described stenosis and collapsibility indices is a practical and user-friendly alternative to measuring the absolute airway diameter (9). In fact, attempts to calculate the airway CSA are impractical for irregular airway morphologies, even for a known airway diameter. The study by Begnaud and colleagues in this month’s issue of AnnalsATS (pp. 85–90) analyzed current practices of quantifying CAO among members of American Association of Bronchology and Interventional Pulmonology (11). The study was performed by a survey-based method and hence suffers from potential recall and selection bias. One hundred eighteen survey responses were eventually analyzed. Each responder was asked to evaluate still bronchoscopic images of CAO and graded them on a numerical scale
of 0 to 100. Baseline calculations of the stenosis index were performed using Fuji software analysis, and CSA area was calculated in pixels by software measurement tools in the region of polygon selection. Previously described bronchoscopic image acquisition techniques were not used, and hence accuracy of initial measurement may have been compromised and potentially inadvertently resulted in a false baseline reference standard (8). Indeed, distance image distortion invariably affects the estimation of degree of CAO. This has been previously demonstrated and thoroughly described in published reviews of morphometric bronchoscopy. The responses of numerical analysis of CAO were compared with previously calculated baseline. Statistical analysis of the means was calculated on the basis of lesion type and previous experience. Opinions and practices from all responders were solicited in free text form and tabulated. Bronchoscopists either under- or overestimate the degree of stenosis when using still image analysis (9). Assessments of bronchoscopy videos may actually result in more accurate estimation of reduction in CSA, but this hypothesis has to be further studied. The study by Begnaud and colleagues supports the results from a previous study, in that there is no statistical correlation between the number of procedures performed and accurate subjective assessment of CAO (9). Most participants in this study agreed that an accurate and precise method should be used for quantification of CAO. Paradoxically, none of the participants surveyed reported use of quantitative
(Received in original form November 15, 2014; accepted in final form November 27, 2014 ) Correspondence and requests for reprints should be addressed to Septimiu D. Murgu, M.D., University of Chicago, 5841 S. Maryland Ave, MC6076, Chicago, IL 60637. E-mail: [email protected] Ann Am Thorac Soc Vol 12, No 1, pp 109–110, Jan 2015 Copyright © 2015 by the American Thoracic Society DOI: 10.1513/AnnalsATS.201411-523ED Internet address: www.atsjournals.org
Editorials
109
EDITORIALS or semiquantitative techniques of morphometric bronchoscopy for CAO measurements. No descriptive responses were given as to why quantitative measures were not being used in clinical practice. The study by Begnaud and colleagues also highlights the fact that in the era of evidence-based medicine and electronic medical records in which accurate data acquisition and processing may directly correlate with treatment decisions and outcomes, we still rely on guesswork or “experience” to assess the degree of CAO. As shown in previous studies, subjective estimates do not measure up to objective quantitative assessments such as morphometric bronchoscopy. The authors conclude by stating that precise and easy-to-use assessment tools for CAO are needed. In this regard, morphometric bronchoscopy aims to reduce the need for subjective estimates and error. However, most likely because of a delay of “real time” assessment and postprocedural time spent
on image analysis and quantification, this technique is not a widely used modality, as evident from the study by Begnaud and colleagues. In addition, noninvasive and physiological assessment tools for airway obstruction may be more valuable to the practicing bronchoscopists. Lateral airway pressure difference, as measured by a double lumen catheter, closely correlates with the critical CAO site identification and guides decisions regarding stent insertion at the flow-limiting segments (12). Noninvasive techniques may also play a pivotal role in correctly identifying the location of CAO and providing objective assessments after interventions (13). The future of morphometric bronchoscopy will likely consist of an integrated, automated, real-time modality that would be capable of obtaining accurate measurements of the airway lumen at the regions of interest. Novel bronchoscopes with two independent lenses at the tip of the device have been proposed (i.e., stereovision
References 1 Myer CM III, O’Connor DM, Cotton RT. Proposed grading system for subglottic stenosis based on endotracheal tube sizes. Ann Otol Rhinol Laryngol 1994;103:319–323. 2 Miller RD, Hyatt RE. Evaluation of obstructing lesions of the trachea and larynx by flow-volume loops. Am Rev Respir Dis 1973;108:475–481. 3 Polverosi R, Vigo M, Baron S, Rossi G. Evaluation of tracheobronchial lesions with spiral CT: comparison between virtual endoscopy and bronchoscopy [in Italian]. Radiol Med (Torino) 2001;102:313–319. 4 Husein M, Manoukian JJ, Platt R, Patenaude Y, Drouin S, Giguere ` C. Ultrasonography and videobronchoscopy to assess the subglottic diameter in the paediatric population: a first look. J Otolaryngol 2002; 31:220–226. 5 Nobuyama S, Kurimoto N, Matsuoka S, Inoue T, Shirakawa T, Mineshita M, Miyazawa T. Airway measurements in tracheobronchial stenosis using endobronchial ultrasonography during stenting. J Bronchology Interv Pulmonol 2011;18:128–132. 6 Murgu SD. Optical coherence tomography of the airways. Curr Respir Care Rep 2014;3:13–18. 7 Shirakawa T, Imamura F, Hamamoto J, Shirkakusa T. A case of successful airway stent placement guided by endobronchial ultrasonography. J Bronchology Interv Pulmonol 2004;11:45–48.
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bronchoscopy), which allow measurement of airway size, using the principle of triangulation, and correlate with computed tomography measurements (14). To date, however, no real-time data acquisition and processing systems are commercially available for measuring airway diameters or CSA (14). Image processing, complex calibration, and distortion image correction could be standardized, and image acquisition will remain the only operatordependent variable. This can be easily achieved, however, by properly controlling the bronchoscope during the procedure. In addition, a closer collaboration between parties involved (i.e., manufacturers, technical engineers, and bronchoscopists) may be helpful in designing bronchoscopes that fulfill the characteristics required for an objective, easy-to-use modality that eliminates guesswork all together. n Author disclosures are available with the text of this article at www.atsjournals.org.
8 Murgu S, Colt HG. Morphometric bronchoscopy in adults with central airway obstruction: case illustrations and review of the literature. Laryngoscope 2009;119:1318–1324. 9 Murgu S, Colt H. Subjective assessment using still bronchoscopic images misclassifies airway narrowing in laryngotracheal stenosis. Interact Cardiovasc Thorac Surg 2013;16:655–660. 10 Elliott EA, Dawson SV. Test of wave-speed theory of flow limitation in elastic tubes. J Appl Physiol 1977;43:516–522. 11 Begnaud A, Connett JE, Harwood EM, Jantz MA, Mehta, HJ. Measuring central airway obstruction: what do bronchoscopists do? Ann Am Thorac Soc 2015;12:85–90. 12 Nishine H, Hiramoto T, Kida H, Matsuoka S, Mineshita M, Kurimoto N, Miyazawa T. Assessing the site of maximal obstruction in the trachea using lateral pressure measurement during bronchoscopy. Am J Respir Crit Care Med 2012;185:24–33. 13 Handa H, Huang J, Murgu SD, Mineshita M, Kurimoto N, Colt HG, Miyazawa T. Assessment of central airway obstruction using impulse oscillometry before and after interventional bronchoscopy. Respir Care 2014;59:231–240. 14 Hayashi A, Takanashi S, Tsushima T, Denpoya J, Okumura K, Hirota K. New method for quantitative assessment of airway calibre using a stereovision fibreoptic bronchoscope. Br J Anaesth 2012;108: 512–516.
AnnalsATS Volume 12 Number 1 | January 2015
