Am. J. Respir. Crit. Care Med., Volume 159, Number 5, May 1999, 1405-1411

Relationship between Resting Hypercapnia and Physiologic Parameters before and after Lung Volume Reduction Surgery in Severe Chronic Obstructive Pulmonary Disease

DANIEL SHADE Jr., FRANCIS CORDOVA, YAROSLAV LANDO, JOHN M. TRAVALINE, SATOSHI FURUKAWA, ANNE MARIE KUZMA, and GERARD J. CRINER

Division of Pulmonary and Critical Care Medicine, and Department of Surgery, Temple University School of Medicine, Philadelphia, Pennsylvania

Patients with severe chronic obstructive pulmonary disease (COPD) have varying degrees of hypercapnia. Recent studies have demonstrated inconsistent effects of lung volume reduction surgery (LVRS) on Pa_CO2; however, most series have excluded patients with moderate to severe hypercapnia. In addition, no study has examined the mechanisms responsible for the reduction in Pa_CO2 post-LVRS. We obtained spirometry, body plethysmography, diffusion capacity, respiratory muscle strength, 6-min walk test, and incremental symptom-limited maximal exercise data in 33 consecutive patients pre- and 3 to 6 mo post-LVRS, and explored the relationship between changes in Pa_CO2 and changes in the measured physiologic variables. All patients underwent bilateral LVRS via median sternotomy and stapling resection by the same cardiothoracic surgeon. Patients were 57 ± 8 yr of age with severe COPD, hyperinflation, and air trapping (FEV₁, 0.73 ± 0.2 L; TLC, 7.3 ± 1.6 L; residual volume [RV], 4.8 ± 1.4 L), and moderate resting hypercapnia (Pa_CO2, 44 ± 7 mm Hg; range, 32 to 56 mm Hg). Post-LVRS, Pa_CO2 decreased by 4% (Pa_CO2 pre 44 ± 7 mm Hg, Pa_CO2 post 42 ± 5 mm Hg; p = 0.003). Patients with higher baseline values of Pa_CO2 had the greatest reduction in Pa_CO2 post-LVRS (r = 0.61, p < 0.001). Significant correlations existed between reduction in Pa_CO2 and changes in FEV₁ (r = 0.56; p = 0.0007), maximal inspiratory pressure (PI_max) (r = 0.46; p = 0.009), diffusing capacity of the lungs for carbon monoxide (DL_CO) (r = 0.47; p = 0.008), and RV/TLC (r = 0.41; p = 0.02). Correlation existed also between reduction in Pa_CO2 and breathing pattern at maximal exercise: maximal minute ventilation ( E_max) (r = 0.47; p = 0.009), and tidal volume (VT) (r = 0.40; p = 0.02). The changes in Pa_CO2 post-LVRS showed marked intersubject variability. We conclude that LVRS, by reducing hyperinflation, air trapping, and improving respiratory muscle function, enables the lung and chest wall to act more effectively as a pump, thereby increasing alveolar ventilation and reducing baseline resting Pa_CO2. In addition, patients with higher baseline levels of Pa_CO2 demonstrate the greatest reduction in Pa_CO2 post-LVRS, and should not be excluded from receiving LVRS.

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