21^st Century Therapies for COPD
Richard Casaburi, Ph.D.,M.D. 
President, PERF

IV. Perfecting Oxygen Therapy

      The list of known effective therapies for COPD is awfully short.  However, we know absolutely, positively for sure that supplemental oxygen delivered by nasal cannula is of benefit for at least a subset of COPD patients.  In some patients, the disease process interferes with the lung’s ability to transfer oxygen from the environment to the arterial blood.  In this case, the level of oxygen in the arterial blood drops substantially, interfering with a multitude of the body’s functions.  This problem is often made worse when the patient exercises; increased demand for oxygen often results in even lower arterial oxygen levels. 

      We know for sure that supplemental oxygen is of benefit because, 20 years ago, enterprising scientists designed a very difficult study.  In the United States, a study spearheaded by our friend Dr. Tom Petty followed for a number of years several hundred patients randomized to receive supplemental oxygen either full time or only part time.  It was crystal clear that, among other benefits, the patients receiving full time oxygen lived considerably longer.  As a result of this study we do not hesitate to prescribe oxygen for patients who have low blood oxygen levels. 

      Why does oxygen work so well?  There are several direct mechanisms of benefit we can point to:  1) The higher levels of arterial oxygen means that more oxygen is supplied to the tissues, 2) The stimulation of the carotid bodies, the sensors of low oxygen level, is decreased resulting in a decreased need to breathe, 3) Increased levels of oxygen dilates the pulmonary arteries (the vessels carrying blood to the lungs), decreasing the stress on the right heart.  These direct effects have a number of consequences including decreased dyspnea and increased exercise tolerance.  In the long term, oxygen supplementation leads to normalized circulating red blood cell count, improvements in the function of the pulmonary blood vessels, better mental function and, as mentioned above, prolonged life expectancy.  If oxygen were a drug, it would be considered a miracle drug!

      But oxygen isn’t a drug.  For a full time oxygen supply, each day the average patient will need a volume of supplemental oxygen roughly equal to the volume of three average sized rooms.   While pure oxygen is relatively easy to manufacture at central locations, packaging it and getting it to the patient has been a genuine inconvenience.  Compressed oxygen tanks were the first method of oxygen supply to be utilized widely.  Later, the transportation of liquid oxygen became practical.  This had the advantage of providing a highly concentrated oxygen source, though it was essential that heat loss was minimized.  A major advance was the invention of oxygen concentrators.  These devices separate oxygen from nitrogen in the atmosphere and eliminate the requirement that oxygen be delivered to the patient.  However, these devices are bulky, often noisy and consume an appreciable amount of electrical power. 

      Two methods have been developed to conserve supplemental oxygen, so the patient can make a given amount of oxygen supply go farther.  Transtracheal oxygen methodology delivers oxygen directly into the windpipe in the neck; often a 50% saving in oxygen supply is possible.  Oxygen conserver devices cleverly restrict the delivery of oxygen via nasal cannula to the times in which it will do the most good.  Clearly, oxygen delivered during exhalation does no good.  It has been discovered that delivering oxygen in a pulse at the beginning of inspiration is very efficient.  These devices yield at least 50% oxygen savings and often considerably more. 

      A special concern has been that the oxygen-dependent patient not be limited in mobility.  Tethering the patient to a stationary supply directly decreases quality of life and limits the opportunity for the patient to exercise regularly.  It is widely recommended that patients who are ambulatory receive a portable oxygen source.  The minimalist way of doing this is to provide the patient with a (stationary) concentrator with a small compressed oxygen cylinder, which can be wheeled around on a small cart.  However, better devices have been perfected.  I believe that the standard of care now requires that a portable supply be capable of being carried without great strain by the patient (shoulder strap, backpack, etc.).   Small liquid oxygen canisters meet this requirement.  More recently, small light oxygen cylinders have become available (though not widely).  Coupled with oxygen conserving devices, these devices can allow the patient to ambulate for several hours at a time.

      The current status of oxygen therapy cannot be understood without taking political considerations into account.  Federal reimbursement for supplemental oxygen has been trimmed by 30% in recent months.  While the current level of funding may be adequate for the provision of stationary oxygen sources (mostly concentrators), portable oxygen supplies are generally more expensive and are threatened by these funding cuts. 

      Political problems require political action.  The 5^th Oxygen Consensus Conference was organized by Dr. Thomas Petty and held in Washington D.C. in late September, 1999.  This was a convocation of scientists, physicians, health care providers, patients and oxygen suppliers designed to develop a prioritized action plan for promoting the utility of this important therapy.  This was a highly successful meeting and the final recommendations are being honed at the time of this writing. 

      I predict that two major developments will change the way we prescribe oxygen therapy.  The first one is technologic – and the wait may not be long.  We need ways to provide portable oxygen in cheaper and more convenient configurations.  Already, devices are becoming available that let oxygen concentrators fill small compressed oxygen cylinders.  What’s next?  Perhaps home sources that produce liquid oxygen.  Maybe even smaller (and lighter) portable liquid oxygen containers.  Maybe even a portable oxygen concentrator.  Probably better conserver technologies.  Keep a look out for these new developments.

      The other developments must come in our understanding of how supplemental oxygen works its wonders and in what circumstances it is of benefit.  A major well-designed study is needed to examine whether providing patients with portable as well as stationary oxygen supplies improves their quality of life and prolongs life.  What of those patients who have low arterial oxygen levels during ambulation, but not at rest?  Do these patients benefit demonstrably from providing them with oxygen only during exercise?  The same question can be asked for patients who only require oxygen when they sleep.  Finally, there is evidence that patients whose oxygen levels are not critically low are able to improve exercise tolerance if provided with supplemental oxygen.  Should we be giving all patients supplemental oxygen when they undergo exercise training programs as part pulmonary rehabilitation?

      Keep well and happy.    

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