A pilot study of expiratory flow limitation and lung volume reduction surgery

Abstract

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.