Airway Surgery for Laryngotracheal Stenosis During the COVID-19 Pandemic: Institutional Guidelines

A computational analysis on the impact of multilevel laryngotracheal stenosis on airflow and drug particle dynamics in the upper airway

Laryngotracheal stenosis (LTS) is a type of airway narrowing that is frequently caused by intubation-related trauma. LTS can occur at one or multiple locations in the larynx and/or trachea. This study characterizes airflow dynamics and drug delivery in patients with multilevel stenosis. Two subjects with multilevel stenosis (S1 = glottis + trachea, S2 = glottis + subglottis) and one normal subject were retrospectively selected. Computed tomography scans were used to create subject-specific upper airway models. Computational fluid dynamics modeling was used to simulate airflow at inhalation pressures of 10, 25, and 40 Pa, and orally inhaled drug transport with particle velocities of 1, 5, and 10 m/s, and particle size range of 100 nm-40 µm. Subjects had increased airflow velocity and resistance at stenosis with decreased cross-sectional area (CSA): S1 had the smallest CSA at trachea (0.23 cm2) and resistance = 0.3 Pa·s/mL; S2 had the smallest CSA at glottis (0.44 cm2), and resistance = 0.16 Pa·s/mL. S1 maximal stenotic deposition was 4.15% at trachea; S2 maximal deposition was 2.28% at glottis. Particles of 11-20 µm had the greatest deposition, 13.25% (S1-trachea) and 7.81% (S2-subglottis). Results showed differences in airway resistance and drug delivery between subjects with LTS. Less than 4.2% of orally inhaled particles deposited at stenosis. Particle sizes with most stenotic deposition were 11-20 µm and may not represent typical particle sizes emitted by current-use inhalers.

Comparison of Inhaled Drug Delivery in Patients With One- and Two-level Laryngotracheal Stenosis

OBJECTIVES/HYPOTHESIS

Laryngotracheal stenosis (LTS) is a functionally devastating condition with high respiratory morbidity and mortality. This preliminary study investigates airflow dynamics and stenotic drug delivery in patients with one- and two-level LTS.

STUDY DESIGN

A Computational Modeling Restropective Cohort Study.

METHODS

Computed tomography scans from seven LTS patients, five with one-level (three subglottic, two tracheal), and two with two-level (glottis + trachea, glottis + subglottis) were used to reconstruct patient-specific three-dimensional upper airway models. Airflow and orally inhaled drug particle transport were simulated using computational fluid dynamics modeling. Drug particle transport was simulated for 1-20 μm particles released into the mouth at velocities of 0 m/s, 1 m/s, 3 m/s, and 10 m/s for metered dose inhaler (MDI) and 0 m/s for dry powder inhaler (DPI) simulations. Airflow resistance and stenotic drug deposition in the patients' airway models were compared.

RESULTS

Overall, there was increased airflow resistance at stenotic sites in subjects with two-level versus one-level stenosis (0.136 Pa s/ml vs. 0.069 Pa s/ml averages). Subjects with two-level stenosis had greater particle deposition at sites of stenosis compared to subjects with one-level stenosis (average deposition 2.31% vs. 0.96%). One-level stenosis subjects, as well as one two-level stenosis subject, had the greatest deposition using MDI with a spacer (0 m/s): 2.59% and 4.34%, respectively. The second two-level stenosis subject had the greatest deposition using DPI (3.45%). Maximum deposition across all stenotic subtypes except one-level tracheal stenosis was achieved with particle sizes of 6-10 μm.

CONCLUSIONS

Our results suggest that patients with two-level LTS may experience a more constricted laryngotracheal airflow profile compared to patients with one-level LTS, which may enhance overall stenotic drug deposition.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:366-374, 2023.