Am. J. Respir. Crit. Care Med., Volume 160, Number 3, September 1999, 883-886

The Impact of Morbid Obesity on Oxygen Cost of Breathing (O_2RESP) at Rest

JOHN P. KRESS, ANNE S. POHLMAN, JOHN ALVERDY, and JESSE B. HALL

Department of Medicine, University of Chicago, Chicago, Illinois

Oxygen consumption dedicated to respiratory work ( O_2RESP) during quiet breathing is small in normal patients. In the morbidly obese, at high minute ventilations, O_2RESP is greater than in normal patients, but O_2RESP during quiet breathing in these patients is not known. We postulated that such patients have increased O_2RESP at rest which may predispose them to respiratory failure when additional respiratory workloads are imposed. We measured baseline O₂ in morbidly obese patients immediately prior to gastric bypass surgery and again after intubation, mechanical ventilation, and paralysis, and compared their change in O₂ to nonobese patients scheduled for elective abdominal surgery. Baseline O₂ was higher in the obese patients compared with control patients (354.6 versus 221.4 ml/min; p = 0.0001) and the change in O₂ from spontaneous breathing to mechanical ventilation was significant in the obese patients (354.6 versus 297.2 ml/min; p = 0.0002) but not the control patients (221.4 versus 219.8 ml/min; p = 0.86). We conclude that morbidly obese patients dedicate a disproportionately high percentage of total O₂ to conduct respiratory work, even during quiet breathing. This relative inefficiency suggests a decreased ventilatory reserve and a predisposition to respiratory failure in the setting of even mild pulmonary or systemic insults.

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