As an emergency medical provider one of the only treatments that you can give is oxygen therapy and it is indicated in nearly every emergency patient. It certainly can do no harm to just give your patient more oxygen, right?
WRONG.
High flow oxygen is actually contraindicated in acutely exacerbated COPD patients. As we have recently learned, COPD is a disorder that increases pulmonary airway resistance, which makes it harder for air to get out of the lungs. We also learned that we have 2 types of chemoreceptors that help regulate respiratory rate-- O2 and CO2 receptors-- such that when CO2 levels are high, we increase our respiratory rate to exhale the excess CO2 and when O2 levels are low, we also increase our respiratory rate to increase O2 levels. A healthy patient relies more on the CO2 chemoreceptors because they are more sensitive than the O2 receptors.
Back to our COPD patient: Because these patients are constantly prolonging their maximum expiration time, they have chronically high levels of CO2 in the blood. These constant elevated levels eventually make the CO2 chemoreceptors less responsive to change, therefore causing the patient to rely more heavily on the O2 chemoreceptors. So now, our patient is relying on low oxygen levels to increase respiratory rate to blow off excess CO2. But if we give this patient high flow oxygen, then we are exacerbating the problem because the O2 receptors will decrease respiratory rate as there are high levels of supplemental O2, so there is a further build-up of CO2 in the blood potentially leading to respiratory acidosis (Barbera, 1997).
Long story short, what seems to be an effective treatment for a patient in respiratory distress could be ineffective and potentially harmful.
https://www-ncbi-nlm-nih-gov.dml.regis.edu/pubmed/9192930
I work in an ER and see patients with acute COPD exacerbation nearly every other shift, so this is really interesting for me to learn about! Given my role as a scribe, I have a lot of experience with thinking the way that an EM physician does and understanding their mindset on what steps are most necessary from an emergency standpoint.
ReplyDeleteThe first and primary focus of ER treatment is to treat the most pressing and life-threatening issue. While the effects of HOFT (high flow oxygen therapy)-induced hypercapnia (including neurological and cardiorespiratory function depression) and decreasing pH (including respiratory acidosis) are definitely concerning and should be monitored for, these are often the result of long-term or severely elevated PaCO2/low pH from prolonged use or in specific situations. When patients have an acute COPD exacerbation, however, hypoxia a MUCH larger threat, as the effects come on much more quickly than those of elevated PaCO2 and can lead to death much sooner. HOFT is most definitely indicated because of this risk. One literature review cites several examples of when HOFT increases CO2 retention in patients (with some leading to comas over time), however, these effects rapidly resolve after they are taken off the HOFT with no long lasting neurological deficits (Murphy). While the research you cited does find valuable information about the dangers of current treatment methods, I don't think it is reasonable to label a treatment that has been used to save countless lives as "ineffective and harmful" without a bit more nuance. Perhaps long-term use of HFOT is dangerous, but short-term use, especially in the ER, is the best option there is to save lives. The goal of ER physicians is to save/preserve life in acute situations, and once they are somewhat more stable, they can then be transferred to different units for treatment. Weighing out the pros and cons, HFOT for acute COPD exacerbation is the best option for short-term treatment in the ER. After the ER, discretion can be used when considering HOFT for longer term care of those patients.
Vogelsinger, H., Halank, M., Braun, S., Wilkens, H., Geiser, T., Ott, S., Stucki, A., … Kaehler, C. M. (2017). Efficacy and safety of nasal high-flow oxygen in COPD patients. BMC pulmonary medicine, 17(1), 143. doi:10.1186/s12890-017-0486-3
Murphy R, Driscoll P, O'Driscoll R Emergency oxygen therapy for the COPD patient Emergency Medicine Journal 2001;18:333-339.
When I was in training as an EMT, there was also a lot of discussion about how oxygen shouldn't (always) be the default treatment for every one of our patients because of the danger of hyperoxemia, which can induce cerebral vasoconstriction, neuronal cell death and seizures. While this obviously needs more study, the current recommendation is to provide supplemental oxygen during resuscitation but to discontinue it as soon as possible when the patient is breathing on their own. In conjunction with your observations, Cierra, providers and hospitals probably need to think critically about when oxygen is really necessary and adjust their care plans accordingly.
ReplyDeleteGershengorn, H. (2014). Hyperoxemia--too much of a good thing?. Critical care (London, England), 18(5), 556. doi:10.1186/s13054-014-0556-3
So this post, first of all, is awesome. I had never thought about how high flow of oxygen administered to COPD patients might worsen respiratory acidosis, hypercapnia, and breathing problems. I found an article that talks a little bit about this also, and it mentions something called the Haldane effect, which is pretty cool. The article is titled "Oxygen-induced hypercapnia in COPD: myths and facts," and states that Hemoglobin (Hb) can combine with CO2 to form carbamino compounds. Deoxygenated Hb can bind CO2 with a higher affinity than oxygenated, and when patients receive high levels of oxygen (when they receive high flow oxygen therapy), the patient has a harder time getting rid of CO2 via respiration. This is because the affinity of Hb to bind CO2 in order to expel it through the lungs has decreased, thus inducing a rightwards shift in the CO2 dissociation curve. This situation is called the Haldane effect, and the because of it, there is a higher level of PaCO2.
ReplyDeleteNormally, people can reduce this level by increasing their ventilation, but patients with severe COPD are unable to do so, and since they are not able to expel their CO2, their lives are at risk. The article says that this is one reason why the HOFT treatment is so dangerous for people with COPD. The article goes on to state that there is evidence that the best strategy to treat patients with COPD is a titrated oxygen administration that provides an oxygen saturation between 88% and 92%. This might result in the patient receiving enough oxygen to breath sufficiently and carry oxygen to the brain and other vital organs, but not enough to result in severe respiratory acidosis because of low affinity Hb binding to CO2 induced by the extra oxygen.
References:
Abdo, W., & Heunks, L. (2012). Oxygen-induced hypercapnia in COPD: Myths and facts. Critical Care, 16(5). doi:10.1186/cc11475
Link to PDF:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3682248/pdf/cc11475.pdf