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

Study objectives: To examine the relationships between changes in expriator y flow limitation (FL) during anesthesia and postoperative responses to lun g volume I eduction surgery (LVRS). Design: Prospective consecutive case comparison, Seffing: University medical center, Patients: Eight patients with severe emphysema. Interventions: General anesthesia with muscle paralysis and thoracic epidur al analgesia were provided for LVRS via median sternotomy. Measurements: FEV1, functional residual capacity (FRC), and total lung capa city (TLC) were measured preoperatively and 3 months postoperatively. Tidal volume (V-T) flow/volume (F/V) curves were obtained with a Pitot-type spir ometer. VT, expiratory flow rate at 0.25 x VT (V'VT,25% ), and peak expirat ory flow rate (V'VT,MAX) were obtained ft om VT F/V curves to derive V'VT,2 5%,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 a SID) and four patients without FL (group B) whose V'VT,25%/V'VT,MAX ratio was 0.82 +/- 0.00 (p = 0.0001). Closed chest post-LVRS V'VT,25%/V'VT ,MAX ratio during anesthesia increased by 0.48 +/- 0.08 in group ii compare d with a 0.19 +/- 0.16 reduction in group B (p = 0.0001). Preoperative FEV1 was 0.57 +/- 0.10 L for group ri. vs 0.82 +/- 0.13 L for group B (p = 0.02 ). Postoperative FEVt 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 r eduction in FRC (r(2) = 0.89, p = 0.0004) and FRC/TLC (r(2) = 0.52, p = 0.0 45). Conclusion: Post-LVRS change in V'VT,25%/V'VT,MAX ratio during anesthesia s howed a linear relationship with 3-month postoperative improvement in dynam ic hyperinflation. Thus, V'VT,25%/V'VT,MAX ratio may help provide valuable insights into the intel actions between chest wall recoil, dynamic hyperinf lation, and VT flow rates in patients with severe COPD and LVRS.