Back in August 2006, a rather adventurous group of 13 oxygen-dependent patients with a variety of diagnoses accompanied Tom Petty, MD, and a handful of respiratory therapists, nurses, and members of industry on a Magical Mystery Tour bus ride up to Echo Lake in the Colorado mountains. Ultimately, the bus took us to an elevation of 10,600 feet.
The chief intent of this mountain excursion was to evaluate one of the new breed of portable oxygen concentrators starting at 5,000 feet in Denver and culminating at Echo Lake. The device being evaluated was the recently released Eclipse unit made by SeQual Technologies. Twelve patients were receiving their oxygen via nasal cannula, while one patient used a SCOOP transtracheal oxygen catheter. All patients were given a NONIN pulse oximeter so we could monitor their oxygen saturations both continuously and with spot checks with every gain of 1,000 feet in altitude.
During a planning meeting a week or so before the adventure, I reminded all participating members that we had better have a healthy supply of continuous-flow oxygen available for the trip. I did not raise this point because I was worried about equipment failure or malfunction at altitude. My concerns were driven by the pure physiology of COPD and its extremely variable effect on oxygen saturation—not only between groups of patients but, quite literally, patient to patient.
As we all learned back in our training, COPD is not a homogenous disease. It is rather patchy by nature with varying degrees of effect on ventilation/perfusion (V/Q) ratio. The uneven matching of ventilation and perfusion is what I believe to be primarily responsible for the incredible variability in a COPD patient’s response to oxygen via either pulse dose or continuous flow. These effects are maximized with even the slightest physical efforts, including routine activities of daily living. I have found over the past 20 years that matching an inspired oxygen molecule with a nearby capillary is easy to draw on the chalkboard, but quite a bit harder to do in the lungs of a real live COPD patient. This dilemma has been exacerbated to an extent with the development of oxygen-conserving technology.
|Dr Petty’s Gang|
While our grand trip up the mountain could not be considered rigorous science, we did glean certain facts. First, the Eclipse unit was very reliable and worked as advertised for most of the patients, most of the time, proving once again there is no “one size fits all” when it comes to pulse technology. The fact that the Eclipse unit has a 3 L/min continuous mode available also proved to be helpful for certain patients at certain times. Many adjustments to flow rate were made on the way up and down the mountain. This raises the very important question of “liter flow equivalent.” Although the industry responsible for all conserving devices, including the new POCs, has done its best to educate physicians and other clinicians as to the difference between the “number setting” and the fact that it is not truly a liter flow equivalent, there is still some confusion regarding just what the setting on any pulse device really represents. Add factors such as different principles of operation, sensitivity to patient inspiration, and exactly where in the first 150 milliseconds of inspiration the breath is delivered, and you can see where much of the confusion comes from. If we as clinicians are confused, how confused do you think our oxygen-dependent patients must be?
This logically leads to a more complete understanding and discussion of no longer using (and confusing) clinicians and patients alike with talk of liter flow equivalent. We should now be talking about a simple flow setting. Actually, the actual number setting should be irrelevant. Why? Because the goal of oxygen-conserving technology should never have been oxygen conservation at the expense of oxygen saturation! This, unfortunately, has been the case for so many years that it has now become a very big ship to turn around in an even bigger ocean. Oxygen is the only drug ever proven to extend life, especially when combined with portability and pulmonary rehabilitation. Petty himself has been talking for the past 40 years about the importance of the adequacy of oxygen delivery to the tissues. I could not agree more. Talk about end points! Without adequate internal respiration, there is not enough oxygen for the mitochondria to produce the necessary energy for normal function of tissues and organs. Without energy, there are no activities of daily living, ie, no real quality of life for our patients.
In summary, my ride up the mountain with Petty stimulated me to go all the way back to the advanced anatomy and physiology courses I took in RT school. My caveat to all practicing RTs is simple: Please do not forget to remember the incredible impact of ventilation-perfusion ratios, as well as other physiologic parameters, when you are considering using any oxygen-conserving device, especially with increased activity or exercise. By the way, this goes for your patients on continuous oxygen as well! Petty has quoted something the great British physiologist John Scott Haldane said in 1913 many times over the years: “Partial anoxia not only means a slowing down of life, but perhaps progressive and irreparable damage to human structure.” It is now 2007, and Haldane’s words still ring true. Quoting Petty now, it is a simple, yet critical extension of Haldane’s words—”titrate when you migrate.”
John Goodman, BS, RRT, is a clinical educator in Colorado. For more information, contact John at