The Effect of Massive Weight Loss on Arterial Oxygenation and Pulmonary Function Tests

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Abstract
Pulmonary function tests (PFT) and arterial oxygenation were studied 24 h preoperatively and again at varying times (5-20 mo.) during the postoperative weight loss of 37 morbidly obese patients. Among PFT, 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 [forced expiratory volume in 1S], FVC [forced vital capacity] or MMEF [maximum midexpiratory flow]. 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 PaO2 [arterial] (r = 0.59, P < 0.05) and P(A-a)O2 [alveolo-arterial gradient] (r = 0.76, P < 0.01). When weight loss is expressed as change in body mass index (.DELTA.BMI) or as a change in percent of ideal weight (.DELTA.wt), there existed a weight loss threshold for improvement in arterial oxygenation. A .DELTA.BMI of > 20 or a .DELTA. wt > 100% resulted in a significant improvement in PaO2 (P < 0.01) or P(A-a)O2 (P < 0.05). Morbidly obese patients evidently do not meaningfully improve FEV1, FVC, or MMEF with massive weight loss. There is a significant improvement in ERV that directly correlates with improvement in PaO2 and P(A-a)O2.

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