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A Pilot Study of Expiratory Flow Limitation and Lung Volume Reduction Surgery^*

^* From the Departments of Anesthesiology (Drs. Dueck and Cooper), Surgery (Dr. Kapelanski), and Medicine (Drs. Colt and Clausen), University of California, San Diego and Veterans Affairs Medical Center, San Diego, CA.

Correspondence to: Ron Dueck, MD, 3350 La Jolla Village Dr, San Diego, CA 92161-5085; e-mail: rdueck{at}ucsd.edu

Study objectives: To examine the relationships between changes in expiratory flow limitation (FL) during anesthesia and postoperative responses to lung volume reduction surgery (LVRS).

Design: Prospective consecutive case comparison.

Setting: University medical center.

Patients: Eight patients with severe emphysema.

Interventions: General anesthesia with muscle paralysis and thoracic epidural analgesia were provided for LVRS via median sternotomy.

Measurements: FEV₁, functional residual capacity (FRC), and total lung capacity (TLC) were measured preoperatively and 3 months postoperatively. Tidal volume (VT) flow/volume (F/V) curves were obtained with a Pitot-type spirometer. VT, expiratory flow rate at 0.25 x VT (V'VT,25% ), and peak expiratory flow rate (V'VT,MAX) were obtained from VT F/V curves to derive V'VT,25%/V'VT,MAX ratio as a measure of FL.

Results: Closed chest VT F/V curves during anesthesia pre-LVRS showed four patients with FL (group A) whose V'VT,25%/V'VT,MAX ratio was 0.38 ± 0.06 (mean ± SD) and four patients without FL (group B) whose V'VT,25%/V'VT,MAX ratio was 0.82 ± 0.06 (p = 0.0001). Closed chest post-LVRS V'VT,25%/V'VT,MAX ratio during anesthesia increased by 0.48 ± 0.08 in group A, compared with a 0.19 ± 0.16 reduction in group B (p = 0.0001). Preoperative FEV₁ was 0.57 ± 0.10 L for group A vs 0.82 ± 0.13 L for group B (p = 0.02). Postoperative FEV₁ increased by 67 ± 40% for group A (p = 0.03) vs 29 ± 21% for group B (not significant). FRC decreased by 33 ± 3% for group A vs 17 ± 5% for group B (p = 0.0007), and FRC/TLC decreased by 0.14 ± 0.05 for group A vs 0.01 ± 0.07 for group B (p = 0.026). Post-LVRS V'VT,25%/V'VT,MAX ratio change during anesthesia correlated with postoperative reduction in FRC (r² = 0.89, p = 0.0004) and FRC/TLC (r² = 0.52, p = 0.045).

Conclusion: Post-LVRS change in V'VT,25%/V'VT,MAX ratio during anesthesia showed a linear relationship with 3-month postoperative improvement in dynamic hyperinflation. Thus, V'VT,25%/V'VT,MAX ratio may help provide valuable insights into the interactions between chest wall recoil, dynamic hyperinflation, and VT flow rates in patients with severe COPD and LVRS.

Key Words: COPD • dynamic hyperinflation • emphysema • expiratory flow limitation • flow/volume curve • lung volume reduction surgery