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

Abstract

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 PaCO2; however, most series have excluded patients with moderate to severe hypercapnia. In addition, no study has examined the mechanisms responsible for the reduction in PaCO2 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 PaCO2 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 (PaCO2, 44 +/- 7 mm Hg; range, 32 to 56 mm Hg). Post-LVRS, PaCO2 decreased by 4% (PaCO2 pre 44 +/- 7 mm Hg, PaCO2 post 42 +/- 5 mm Hg; p = 0.003). Patients with higher baseline values of PaCO2 had the greatest reduction in PaCO2 post-LVRS (r = -0.61, p < 0.001). Significant correlations existed between reduction in PaCO2 and changes in FEV1 (r = -0.56; p = 0.0007), maximal inspiratory pressure (PImax) (r = -0.46; p = 0.009), diffusing capacity of the lungs for carbon monoxide (DLCO) (r = -0.47; p = 0.008), and RV/TLC (r = 0.41; p = 0. 02). Correlation existed also between reduction in PaCO2 and breathing pattern at maximal exercise: maximal minute ventilation (V Emax) (r = -0.47; p = 0.009), and tidal volume (VT) (r = -0.40; p = 0.02). The changes in PaCO2 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 PaCO2. In addition, patients with higher baseline levels of PaCO2 demonstrate the greatest reduction in PaCO2 post-LVRS, and should not be excluded from receiving LVRS.

Effect of lung transplant and volume reduction surgery on respiratory muscle function

“…Several studies have assessed the effects of LVRS on diaphragm strength by measuring Pdi sniff , Pdi max , or Pdi tw before, and 1 to 24 mo after the procedure (2, 12, 26, 29 -32, 41, 53, 58). These studies are qualitatively consistent, all showing an increase in the pressure-generating capacity of the muscle after surgery; four studies also showed increases in MIP (12,41,53,58). The increase in MIP and Pdi sniff was already present at 1 mo after LVRS in one study (58), and in the study by Bellemare et al (2), Pdi max (but not Pdi tw ) continued to increase throughout the first postoperative year.…”

Lung Transplantation and Lung Volume Reduction Surgery versus Transplantation in Chronic Obstructive Pulmonary Disease

“…A study by Yusen and coworkers showed that the proportions of patients using supplemental oxygen at rest and with exercise fall significantly 6 months after LVRS (53 to 15% for use at rest and 95 to 46% for use on exercise) (41). Although patients with severe hypercapnia were excluded from most studies, patients with modest hypercapnia did show improvement to the normal or near-normal range (41,42).…”

Bronchoscopic lung volume reduction: indications, effects and prospects

“…This mechanism may more properly be thought of as a measurement error, although it does reflect emphysematous pathophysiology. Interestingly, improvements in gas transfer appear to be a consistent feature of BLVR whereas following LVRS, perhaps because the technique inevitably requires the removal of some relatively normal lung tissue, it has not improved in a number of studies [1,20], although this has not been a universal finding [21,22].…”