New and Emerging Minimally Invasive Techniques for Lung Volume Reduction
Emphysema is characterized by destruction of alveolar walls distal to the terminal bronchioles. This process leads to enlargement of distal air spaces with development of emphysematous blebs, cysts, and bullae. Because capillary-rich alveolar walls are also destroyed in areas of emphysema, these enlarged air spaces have very high ventilation/perfusion
(V/Q) ratios creating physiologic dead space. Increased dead space ventilation reduces efficiency of breathing, resulting in increased work and impaired gas exchange.
The destruction of alveolar walls also leads to decreased alveolar elastic recoil and decreased traction support of small airway lumens, leading to impaired exhalation. Reduced elastic recoil combined with expiratory airway collapse causes hyperinflation and air trapping in overly compliant emphysematous areas of lung. This hyperinflation can compress areas of more normal lung, leading to reduced ventilation in areas of lung that are well perfused. The resulting low V/Q ratios in areas of compressed lung further impair gas exchange, leading to hypoxemia.
Lung volume reduction surgery (LVRS) with surgical removal of hyperinflated poorly perfused areas of lung has been shown in numerous uncontrolled and controlled studies to benefit patients with emphysema. Functional, physiologic, and quality-of-life benefits have been demonstrated. These positive results have been validated by the recently reported National Emphysema Treatment Trial (NETT), which also demonstrated a survival benefit following LVRS for patients with upper-lobe heterogeneous emphysema and limited exercise capacity.
The encouraging results from the NETT confirm the value of removing hyperinflated, nonfunctioning areas of lung in patients with emphysema. Although the surgical morbidity and mortality data in the NETT study are acceptable, LVRS remains a major surgical procedure requiring general anesthesia and postoperative intensive care. LVRS is associated with potential complications including prolonged air leak, which can lead to lengthy hospitalization. The NETT study also identified a group of patients with very severe emphysema (FEV1 < 20% and either diffusing capacity of the lung for carbon monoxide [Dlco] < 20% or homogeneous emphysema) who had unacceptably high 30-day mortality (16%) from LVRS.