LAUSR

Emphysema is characterized by alveolar destruction distal to the terminal bronchioles causing hyperinflation and reduced gas exchange, resulting in dyspnea, and exercise limitation. Lung volume reduction surgery (LVRS) of the hyperinflated emphysematous lung improves elastic recoil and neuromechanical coupling of respiratory muscles, and redirects ventilation to lung segments with better perfusion.1 In a randomized controlled trial, LVRS in selected patients with upper lobe predominance obtained improvements in symptoms, lung function, exercise tolerance and quality of life relative to the medically treated control group.2 LVRS, however, carries significant morbidity and mortality.3 Complications including prolonged air leaks, as well as respiratory and/or cardiac complications with prolonged hospital stays, and have limited the adoption of LVRS as routine therapy for patients with severe emphysema. Subsequently, various bronchoscopic techniques have emerged to achieve lung volume reduction with an improved safety profile. One such method is bronchoscopic thermal vapor ablation (BTVA). BTVA uses heated water vapor that is administered to targeted regions of the lung to produce a thermal reaction leading to an initial localized inflammation followed by permanent fibrosis and volume reduction.4 In a prospective, single-arm trial of 44 patients with upper-lobe predominant emphysema, unilateral BTVA at a vapor dose of 10 cal/g lung tissue resulted in a 48% lobar volume reduction and improvements in lung function, exercise tolerance and other patient reported outcomes.5 Post hoc analyses of the trial cohort, however, indicated that the occurrence of serious adverse events increased with the volume of the treated lobe with an inflection point at 1700 ml target lobar volume.6 Therefore, an alternative approach was required to limit the volume treated per session, which has resulted in the design of the STEP-UP study. The STEP-UP study was a randomized, controlled open-label trial using vapor ablation in a sequential bilateral treatment to