A 55-year-old man presents to the Emergency Room with crushing chest pain. He is diagnosed with an acute heart attack. The nurse, following the American Heart Association Advanced Cardiovascular Life Support guidelines and out of habit, puts the patient on oxygen. A football player comes off the field after a particularly grueling set of plays. He sits on the bench and puts on an oxygen mask. A patient with stable chest pain asks his doctor for oxygen to be used at home. Would oxygen be helpful in any of these scenarios? When is oxygen therapy useful and necessary?
Oxygen was discovered by Joseph Priestly in 1774 and is the second most abundant element in the air (after nitrogen). Oxygen takes up 21% of the Earth’s atmosphere. Oxygen is necessary for all of the functions of the body. As we breathe, the oxygen in the air is brought to tiny sacs in the lungs. In these lung sacs, oxygen is absorbed by the blood stream. In the blood stream, oxygen binds to the red blood cells. The oxygen, attached to red blood cells, travels through the lungs to the heart where it is pumped to the rest of the body. Oxygen is then extracted by the muscles and organs of the body to aid in metabolism.
Since oxygen is so essential to the body, how can we be sure we are getting enough? In medicine, the most common way to measure oxygen is with a pulse oximeter, an infrared device that provides the oxygen saturation in the blood. An oxygen saturation between 90% and 100% is normal while a saturation below 90% is considered low. Low oxygen saturation, or hypoxemia, causes shortness of breath, an increased heart rate and it can be very dangerous. To treat hypoxemia, oxygen therapy is delivered in a variety of ways. A nasal cannula has two prongs, which are placed in the nose, and gives extra oxygen. A facemask can provide higher dosages of oxygen, with concentrations up to 100% (ie, the gas in the mask is 100% oxygen versus the 21% oxygen present in the air). Lastly, in extreme cases of hypoxemia and breathing distress, a tube is placed in the throat and the patient is placed on a respirator to help aid in process of breathing.
Oxygen has been a key treatment in cardiology for more than 100 years. In 1900, it was shown that oxygen could relieve chest pain, a finding that led to the routine use of oxygen in all heart patients. Over the years it has been found that oxygen therapy in patients with hypoxemia is undeniable but in patients with normal oxygen saturation the benefit is not as clear. In patients who are hypoxemic and have an acute heart attack or who are in congestive heart failure (CHF), with fluid filling their lungs, oxygen can be life saving. In cases with hypoxemia, oxygen therapy increases the oxygen saturation in the blood, decreases the resistance to blood flow in the lungs and eases the work of the heart by lowering the heart rate and blood pressure, thus reversing the body’s adaptation to a low saturation.
While the body has mechanisms to counter act low levels of oxygen in the blood, high levels of oxygen saturation is a man-made phenomenon caused by oxygen therapy. The body has no mechanism to handle this situation and in fact oxygen therapy can be damaging. There are two possible reasons for this. First, the red blood cells are nearly saturated with oxygen. Adding extra oxygen doesn’t increase the amount of oxygen delivered to the cells of the body. Secondly, excess oxygen can cause spasm or narrowing of the heart arteries, reducing blood flow to the heart. In CHF patients with normal oxygen saturation, high flow supplemental oxygen caused a decrease in the heart’s pumping capacity and increased the pressure in the lungs, causing worse outcomes. In heart attack patients with normal oxygen saturation, excess oxygen therapy can cause a reduction in flow to the heart arteries. Patients with oxygen therapy had larger heart attacks than those not given extra oxygen. In a recent study of over 6000 patients with a heart attack and normal oxygen saturation, there was no change in the rate of death or recurrent heart attack with oxygen therapy.
Can oxygen be beneficial for the athlete? Can it be considered a performance-enhancing drug? When supplemental oxygen was given to soccer players and other athletes, there was no demonstrated improvement in performance and no reduction in recovery time. On the athletic field, it is felt that oxygen may provide a placebo effect (an expectation of doing something good) without a real physiologic benefit.
Oxygen clearly has a role and is life saving for those heart patients who have low oxygen saturation. For heart patients with normal oxygen levels, as well as football players and other athletes, supplemental oxygen likely has no benefit and can be harmful. Based on these findings, none of the patients in the scenarios would be candidates for supplemental oxygen.
Bridgewater resident Steve Georgeson is a cardiologist who works for Medicor Cardiology. Here, he writes about topics and events pertaining to cardiology
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