Physiology-based minimum clinically important difference thresholds in adult laryngotracheal stenosis

Delivering evidence-based patient care is predicated on the availability of objective and validated outcome measures. We aimed to calculate physiology-based minimum clinically important difference (MCID) values for adult laryngotracheal stenosis (LTS).

Prospective observational study.

Patient demographics, morbidities, and stenosis severity were assessed preoperatively. Flow-volume loops and Medical Research Council (MRC) dyspnea grades were measured in 21 males and 44 females before and 6 to 8 weeks after airway surgery, and before treating recurrent disease in 10 patients. Anchor and distribution-based methodologies were used to calculate MCIDs for treatment efficacy and disease recurrence respectively.

The mean age at treatment was 46 ± 16 years. The most common etiology was idiopathic subglottic stenosis (38%). Most lesions (66%) obstructed >70% of the lumen. There were strong correlations between treatment-related changes in total peak flow (TPF) (ΔTPF) (peak expiratory flow + |peak inspiratory flow|) and the ratio of area under the flow-volume loop (AUC) to forced vital capacity (FVC) (ΔAUCTotal /FVC), and treatment-related changes in the MRC grade (ΔMRC) (r = -0.76 and r = -0.82, respectively). Both TPF and AUCTotal /FVC discriminated between effective (ΔMRC <0) and ineffective (ΔMRC ≥0) interventions, yielding MCID values of 4.2 L/s for TPF and 2.1 L(2) /s for AUCTotal /FVC, respectively. Ten patients required airway treatment for recurrent disease, and TPF and AUCTotal /FVC levels had distribution-based MCID values of 0.9 and 0.6, respectively.

Flow-volume loops provide a quantitative method of objectively assessing outcomes in LTS. TPF is the most convenient index for this purpose, but AUCTotal /FVC provides marginally greater sensitivity and specificity.