An oxygen level in the range you mention (88% or less) is the usual indication for starting oxygen in patients with COPD. It is perhaps easier to answer the question
of what oxygen can do in this situation, rather than what the effects of a low oxygen level are. Studies have shown that oxygen in patients with COPD can prolong life, decrease the amount of red blood cells circulating in the blood stream (which is usually a good thing in patients with COPD because a low oxygen will result in an overproduction of red blood cells), improve blood flow through the lung, and improve thinking/reasoning. I usually tell my patients that oxygen can make them live longer and better. In general oxygen for part of the day is better than no oxygen at all, but the greatest benefits are for those who use oxygen more or less continuously. One important point is to make sure that the COPD is well treated before oxygen is started. For example up to 21% of patients who have a low oxygen in the range you mention, may improve if their COPD treatment is expanded, such that they would no longer need oxygen.