The effect of massive weight loss on arterial oxygenation and pulmonary function tests

Abstract

Pulmonary function tests (PFTs) and arterial oxygenation were studied 24 hours preoperatively and again at varying times (5 to 20 months) during the postoperative weight loss of 37 morbidly obese patients. Among PFTs expiratory reserve volume (ERV) demonstrated the most significant (P < 0.001) improvement with weight loss. No clinically relevant differences were found after weight loss in FEV1, FVC, or MMEF. In 11 patients whose arterial blood gases were sampled before and after weight loss, a significant correlation was demonstrated between change in ERV and change in Pa(O)2 (r = 0.59, P < 0.05) and P(A-a)(O)2 (r = 0.76, P < 0.01). When weight loss is expressed as either change in body mass index (ΔBMI) or as a change in percent of ideal weight (Δwt), there existed a weight loss threshold for improvement in arterial oxygenation. A ΔBMI of greater than 20 or a Δ wt more than 100 per cent resulted in a significant improvement in Pa(O)2 (P < 0.01) or P(A-a)(O)2 (P < 0.05). These data suggest that morbidly obese patients do not meaningfully improve FEV1, FVC, or MMEF with massive weight loss. However, there is a significant improvement in ERV that directly correlates with improvement in both Pa(O)2 and P(A-a)(O)2.