Question

A patient has been Admitted to the medical floor for exacerbation of his COPD. The patient is wearing oxygen at 2 L/min via nasal cannula with a resting SPO2 of 93%. You have been asked to assist in evaluating the patients oxygenation status during ambulation.

How would you titrate the oxygen flow during ambulation? Be specific.

Answer 1

Risks associated with both hypoxemia and hyperoxia have been well described and, consequently, accurate adjustment of oxygen flow rates in COPD patients is of particular importance.

Oxygen therapy is the most frequently administered emergency treatment in hospital and during prehospital care. The adverse effects of hyperoxia are well known in patients with COPD and are particularly marked during exacerbations.

Given the effects of hyperoxia on morbidity and mortality in COPD patients, failure to comply with the recommendations to accurately adjust oxygen flow in patients with COPD could result in avoidable medical complications and significant added costs for the health care system.

Current practice requires manual adjustments of oxygen flow rates via ‘oxygen flowmeters’. One possible modern solution to facilitate knowledge transfer is to automate repetitive and relatively simple medical tasks. The adjustment of oxygen via a closed-loop system is promising. In such systems, the main parameter taken into account is SpO₂, which continuously feeds the algorithm. A proportional integral controller adjusts the oxygen flow within a range (that differs from one device to another), with the aim of maintaining the SpO₂ within a predefined target that can be set by the clinician.

The six-minute walking test is considered a submaximal exercise that can become maximal in some patients, wherein the oxygen consumption correlates well with the peak oxygen consumption obtained by cycle ergometry. However, a patient may not go through desaturation at home if the daily physical activity is low. A patient who does not walk, will obviously not reach desaturation. Outside the hospital, many patients with low mobility will not recreate the pathophysiological conditions that occurred during the walk test in the hospital.

It seems reasonable to assume that early desaturators will benefit from ambulatory oxygen therapy, as they will desaturate during their activities of daily living. Late-onset desaturators will not experience oxygen desaturation in their daily lives. Consequently, they would not benefit from oxygen therapy while walking around. However, depending on the individual case and their activity, those intermediate desaturators—with an onset between 1 and 3.3 min—may go through desaturation at home.

That being said, the question is how to administer the oxygen. We recommend a walk test with oxygen administration while assessing improvements in walking distance, degree of dyspnea, post-exercise recovery period, and the oxygen flow needed for these changes. Thus, titrating their ambulatory oxygen therapy, these patients with usually serious COPD will not desaturate with exercise. As a result of this titration, based on submaximal exercise, the patient will neither desaturate during the walk test nor during activities of daily living. Despite oxygen requirements being somewhat lower, the titer will certainly be set higher to avoid daily desaturation.