Hello doctor, I feel that I am a complicated case and I am trying to figure out the best way to titrate my oxygen treatment. I have late-stage cystic fibrosis, and I am experiencing a few months of exacerbation that has led to me needing oxygen full time. A few weeks ago I began, for the first time, to titrate my O2 saturation vigilantly to between 90-95%, to combat Co2 retention. Previously, even when sick and using O2 full time, I had not retained Co2. But on my recent ER visit when I was in pulmonary distress (very short of breath) my pCo2 was 65. I was advised to titrate it. I had been advised before, but I had not always done so rigorously, because frankly it just felt uncomfortable. This time I stuck to it, however, because I was very nervous about increased Co2 retention. My pCo2 has wavered around, from 65-62-57-62-58, in about three weeks. The thing that has significantly changed, however, is that I am no longer sensitive to low oxygen saturation. My breathing is much more shallow, and I can sit comfortably at 90% and not even feel bad. It is scary because I can also be walking around and desaturating to 85% without even feeling it. I used to be able to know my oxygen saturation just by feel and how short of breath I was. My breathing, as I said, is very shallow even as I desaturate. It is only when I exercise to a certain point, at high levels of O2, that I am able to inhale and exhale involuntarily and deeply. I have some different issues that make me wonder if the protocol for titrating oxygen at low saturations for Co2 retention is the right treatment for me, and I am going in circles trying to figure it out. My doctors do not seem too concerned about my Co2 retention in general, given my late-stage CF and that I am about to be listed for a transplant, but I always want to figure out what is the best thing to be doing. I have a right to left pulmonary shunt. It is demonstrated when I lie down. My O2 saturation actually rises while lying down, and rises higher if I lie on my left side vs right. So I believe that this would be a component in that venous blood is being recycled into arterial blood but I do not have a grasp of how that could effect Co2 retention (only that it can lower my O2 saturation). Secondly, I am very anemic. My hemoglobin has dropped from 9-7 g/dL in the recent three weeks. I have always been anemic, but I have become even more so in the past three weeks, despite having been sick with exacerbations for months. The last three weeks have been different. (For example, I am also experiencing low magnesium for the first time, and we keep supplementing, but I cannot get my levels up). Lastly, my lungs have improved and infection has cleared somewhat, but I have not been able to come closer at all to being off oxygen. I know I do need to accept that maybe this is not a reality. But regardless, my O2 needs are lower, yet as soon as I exercise or move around even a little, they drop rapidly. Before three weeks, it was much less extreme. Now, I can sit resting on 1 liter and have a saturation of 97, yet as soon as I get up and move for 15 seconds, it drops quickly to the 80's. There are all these components, lungs (shot), anemia (no red blood cells to carry), and pulmonary shunt (diversion of oxygenated blood), that I am trying to piece together to figure out if titrating my oxygen to lower numbers is actually helping me or hurting me?
Hello. Well, that was a wonderful and well-detailed query. I will answer your query in parts. Regarding your insensitivity to low O2 saturation: Well, this is an expected development in long-standing lung problems. Continuous exposure to low oxygen levels over long time will decrease the brain's sensitivity for low oxygen and hence that is the reason you breathe shallow in spite of desaturation. So the body's next line of defense for low oxygen is CO2. When the brain's sensitivity to oxygen is reduced then the brain uses CO2 level to trigger breathing. But because of your advanced cystic fibrosis exchange of Co2 and O2 is not happening adequately at the lung level and hence your body is retaining Co2 because it is not able to remove it out. My advice at this point is to do breathing exercises, take long inhalation and long exhalation. Also, do incentive spirometry exercise. Coming to your hypothesis of right to left shunt you are absolutely right. But shunting could be at the lung level or at the heart level. In your case, the chances of shunt being at lung are more likely but still, tests should be done so that there is no shunting at the heart. For that, I advise you get echo with contrast with positional change maneuver. If your venous blood is being recycled into arterial blood then the total Co2 content of the blood increase (as venous blood contains more CO2 than arterial) and thus the Co2 gradient (the difference between arterial Co2 and alveolar or in simple terms lung Co2) decrease and Co2 elimination is directly dependent on Co2 gradient. Higher the gradient more the elimination and less retention and vice versa. Anemia contributing to O2 desaturation and Co2 retention: If you are anemic then your blood carries less O2 so at rest your O2 demands would be less but on exercise your O2 demands increase a lot which cannot be met due to low O2 carrying capacity of your blood, thus leading to profound O2 desaturation. But what is not know is why are you suffering from anemia? What is the cause? Because if we can correct your anemia your O2 requirement even on exercise can come down. I advise if any evaluation from your anemia point of view has been done kindly upload so that I can help further. Until your cardiac evaluation for intra cardiac shunt and anemia evaluation are completed, I advise you to keep titrating your O2 to maintain spo2 > =95% both at rest and on mild exercise. Till correction of any shunt (if possible) and correction of anemia is done you will desaturate on exercise and hence increase O2 during exercise.