Exertional desaturation in patients with chronic obstructive pulmonary disease.

Although the Centers for Medicare and Medicaid Services oxygen prescription guidelines utilize a threshold arterial oxygen tension <or=55 mmHg or an oxygen saturation <or=88%, a range of oxygen levels and relative declines have been used in investigations of exertional desaturation in patients with chronic obstructive pulmonary disease (COPD). There is no uniform definition of exertional hypoxemia or standardized exercise protocol to elicit decreases in oxygen levels in individuals with COPD. The causes for exertional desaturation in patients with COPD are multifactorial with ventilation-perfusion mismatching, diffusion-type limitation, shunting and reduced oxygen content of mixed venous blood all contributing to some degree. Neither resting oxygen saturation nor pulmonary function studies can reliably predict which patients with COPD will develop exertional desaturation. However, preserved pulmonary function, especially diffusing capacity, reliably predicts which patients with COPD will sustain oxygenation during exercise. Although exertional desaturation in patients with COPD appears to portend a poor prognosis, there is no evidence that maintenance of normoxemia during exercise improves the survival of these patients. Studies of the effect of supplemental oxygen on exercise performance in individuals with COPD who desaturate with exertion have yielded conflicting results. The use of short-term or "burst" oxygen either prior to or after exertion may not have significant clinical benefit. Differences in the definition of desaturation, mode of exercise, and characteristics of the patient population make it difficult to compare studies of exertional desaturation and its treatment and to determine their applicability to clinical practice.