Dynamic airway computed tomography and flexible bronchoscopy for diagnosis of tracheomalacia in children: A comparison study
Melissa Brooks Peterson MD and Myron Yaster MD
I’ve got to admit that I never understood the rationale for CT scanning in the aerodigestive workup. Why expose a patient to the enormous radiation exposure of a dual phase CT scan if the patient was also going to undergo the gold standard of bronchoscopy (and GI endoscopy)? Fortunately, the PAAD has Dr. Melissa Brooks Peterson, our resident guru/maven in all things related to the airway and aerodigestive to combat my nihilism on this subject. In today’s PAAD, Corcoran et al.1 compare dynamic flexible bronchoscopy and dynamic computed tomography (DACT) in the diagnosis of tracheomalacia. Myron Yaster MD
Original article
Corcoran A, Foran A, Phinizy P, Biko DM, Piccione JC, Rapp JB. Dynamic airway computed tomography and flexible bronchoscopy for diagnosis of tracheomalacia in children: A comparison study. Pediatr Pulmonol. 2024 Apr;59(4):899-906. doi: 10.1002/ppul.26844. Epub 2024 Jan 10. PMID: 38197524.
“Tracheomalacia (TM) is characterized by increased compliance of either the intra‐or extra‐thoracic trachea resulting in collapse during the respiratory cycle. With intrathoracic TM, airway collapse occurs on exhalation while with extra‐thoracic TM, airway collapse occurs on inspiration. Airway collapse in bronchomalacia occurs solely on exhalation”1 Tracheomalacia remains widely underdiagnosed despite being an important cause of respiratory morbidity.1,2 Dynamic flexible bronchoscopy is considered the gold standard for diagnosing TM as well for evaluating swallowing, laryngeal reflux, and drug‐induced sleep endoscopy (DISE).3 As pediatric anesthesiologists we are keenly aware that bronchoscopy almost always requires general anesthesia in our patient population and can be quite challenging in some of our sicker and more fragile patients. Additionally, general anesthesia may confound the diagnostic results when utilized during these diagnostic studies because, depending on the techniques employed, it may produce atelectasis and the rate and quality of tidal breathing.
Dynamic airway computed tomography (DACT) is a reliable alternative for diagnosis and uses much less radiation than conventional CT scanning with dual phase end-inspiratory and end-expiratory breath holding or fluoroscopy with contrast. Additionally, it may not require general anesthesia. In today’s PAAD, Corcoran et al. assessed the accuracy of low dose DACT with the current gold standard, bronchoscopy. In this study, bronchoscopy was performed within a 6‐month period of the DACT.
Ok, what did they find? “Twenty‐four patients met inclusion criteria with an average time of 19.5 days between CT and bronchoscopy. The specificity and sensitivity of DACT for the overall diagnosis of TM was 100% and 68%, respectively, with a positive predictive value of 100% and a negative predictive value of 62%. There was a strong positive correlation between DACT and flexible bronchoscopy in the measurement of tracheal AP diameter changes (ρ= 0.773,R20.597,p= 0.00001). Mean effective radiation dose for DACT was 0.1 mSv. They concluded that ultralow dose DACT has excellent specificity and positive predictive value for both detection of TM and categorizing severity of tracheal collapse but is not sufficiently sensitive to rule it out.”1
Dynamic imaging modalities are amazing; as many of our pediatric cardiac anesthesia colleagues are aware from the hours they spend in the MRI and CT scanners, CINE imaging and similar modalities which have revolutionized our diagnostic capabilities. Aside from congenital heart disease, these modalities are commonly used in fetal diagnostics and intervention, aerodigestive programs, and many others. Today’s PAAD highlights the potential of DACT and other real-time radiology modalities to replace older diagnostic techniques.
I (Mel) do have some points of criticism that I hope will spark your interest or, at the very least, generate conversation: I think it is vitally important, and a critical error by this author group, that there is not a well-defined anesthetic administered to these patients. Of course, the ideal situation would be a prospective study with a standard anesthetic but that is not the study design. So we are stuck with a retrospective analysis, which has its limitations. My main issue even accepting a retroscpective analysis is that there is complete absence of a reasonable description of the anesthetic conditions! There is some vague accounting of which patient had ETT, which (1 patient) had NIPPV, and the others… unsure. There is reporting of minimal “vent settings” (PEEP) – which is totally insufficient to characterize the ventilatory conditions. Additionally, for the flexible bronchoscopy portion of the data collection, the retrospective review only reports the conduit for the flexible scope (nare, mouth, LMA, or ETT) but fails to meaningfully report any of the other anesthetic conditions. In one instance, there is mention of a failed diagnostic study and possible depth of sedation issue with a significant discord for one patient. We all know that the type, depth, stage, and nuances of the anesthetic administered in these types of studies really does matter! As a deeply invested aerodigestive anesthesiologist, I touch a couple hundred of these patients each year, and I know how to tinker with the caliber, tone, static and dynamic behavior of the trachea using my anesthesia machine and medications. We all know – but this study seems to completely ignore, that the airway device used (or not used), the flow rate on the machine in spontaneous mode, the settings in pressure support mode, and the ventilator mode employed in controlled ventilation really can make a difference on perceived airway caliber, tone, and degree of “malacia”. Additionally, the administration of a variety of medications (sevo/iso, propofol, fentanyl, topical lidocaine, IV lidocaine, dexmedetomidine) can all really alter both the static and dynamic conditions of the trachea – whether you are taking pictures with a flex bronchoscope or a dynamic CT scanner.
What I think would have been a much more effective – and meaningful – addition to make this study really shine is if the author group recognized the value of an airway and aerodigestive-savvy pediatric anesthesiologist, approached that anesthesiologist to be a contributor to the data to help characterize and make sense of the anesthetic conditions for this study population. Then, in addition to some outstanding description of the utility and method of DACT from the radiology team, there would have been an intelligent assessment of the anesthetics administered, and a much more robust discussion about contributions of the anesthetic conditions that (probably) alter the findings on both DACT and flexible bronchoscopy. Additionally, I think that combining their anesthetics into a single radiology-then-triple-scope case would have reduced the patients’ anesthetic exposure, and also ensured that the same anesthesiologist was responsible for both the DACT and flex bronch portion of the case.
My main take aways from this interesting study are: first, DACT is an emerging tool in our medical armamentarium for patients with complex airways, and we should expect to see much more CINE, dynamic, and real-time imaging advances in the next few decades. Second, never underestimate the value of a knowledgeable pediatric anesthesiologist who understands the nuances of static and dynamic airway years, particularly for complex kids with trachea-bronchomalacia, compression, parenchymal lung disease. And don’t forget to offer your expertise or ask to be included in these research studies – it will make these types of studies much better!
Is ultralow dose DACT available in your institution? What other types of CINE, dynamic, or real-time evaluations do you perform or facilitate at your institution? At the very least, shouldn’t it replace the higher radiation dual phase CT examinations typically used in the diagnostic work ups of these patients? Send your thoughts and comments to Myron who will post in a Friday reader response.
References
1. Corcoran A, Foran A, Phinizy P, Biko DM, Piccione JC, Rapp JB. Dynamic airway computed tomography and flexible bronchoscopy for diagnosis of tracheomalacia in children: A comparison study. Pediatr Pulmonol 2024;59(4):899-906. (In eng). DOI: 10.1002/ppul.26844.
2. Ullmann N, Secinaro A, Menchini L, et al. Dynamic expiratory CT: An effective non-invasive diagnostic exam for fragile children with suspected tracheo-bronchomalacia. Pediatr Pulmonol 2018;53(1):73-80. (In eng). DOI: 10.1002/ppul.23831.
3. Mooney KL, Brooks Peterson M, Skirko JR, Friedman NR. The Quest for a DISE Protocol. Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery 2021:1945998211036645. (In eng). DOI: 10.1177/01945998211036645.