Oxygen Use During STEMI: Beneficial or Detrimental?

[Pdwyer1]

Imagine being woken up from your sleep with a sensation that an elephant is sitting on your chest. You get up to take something to try to relieve the pain, but the pain persists and starts to radiate down your left arm. You get yourself to a phone, call 9-1-1 and are promptly transported to the hospital. An ER nurse would be notified of this incoming patient, and properly prepare the room for their arrival. Following MONA, we would have morphine, oxygen, nitroglycerin, and aspirin ready for any orders that the physician might enter. The patient arrives and is placed on oxygen while the physician is putting in his orders since the patient is truly having an ST-elevated myocardial infarction (STEMI). During this event, the physician comes in and takes the oxygen off the patient due to no evidence of hypoxia on arrival. What if using oxygen is not the best treatment? Of course, nitroglycerin will help dilate the vessels, morphine will reduce pain, and aspirin will help reduce clotting, but what if oxygen use during a STEMI is actually detrimental to the patient? Nurses want to provide the best care that is evidence-based. The nurse has many roles during this event, and they certainly do not want to cause more harm to the patient.

A myocardial infarction (MI) is defined as, “a heart condition of sudden onset in which muscle tissue dies because of a lack of blood flow, resulting in varying degrees of chest pain or discomfort, weakness, sweating, nausea and vomiting, and possible loss of consciousness.”¹ It is important to note that not all patients will present the same. Some individuals may report back pain or even jaw pain on arrival. Medical staff has been taught that the purpose of applying oxygen to patients is to increase the tissue oxygenation, reduce pain, and decrease infarct size.² Nurses have been trained and are accustomed to apply oxygen as a first line treatment to help alleviate the pain under the pretense that giving supplemental oxygen leads to an increase of oxygenation in the blood, yet studies are now showing that the use of oxygen can either be detrimental to patients or have little to no beneficial clinical outcomes.

With the use of oxygen during an MI now being controversial, it is important to look at all of the data. During one study, a group of researchers found that the use of oxygen not only led to an increase of recurrent MIs but also led to arrhythmias.³ In addition to recurrent MIs and arrhythmias, their data suggests that the use of supplemental oxygen did not provide any benefit to the patient.³ Oxygen delivery systems, such as face masks or nasal cannula, when applied to patients can make them feel claustrophobic, or they even may feel that they cannot breathe with them on. If nurses and the medical community are able to reduce to that fear by not applying these devices, it could improve patient anxiety prior to a possible cardiac catheterization. If patients develop arrhythmias from oxygen use, it not only complicates care but can delay care as well. A second study found that patients can suffer from reperfusion injuries due to vasoconstriction and an increased production of reactive oxygen species from above-normal oxygen levels in the blood.⁴ The results of this study indicated that oxygen use during an MI did not reduce the one-year all-cause mortality rates⁴. Injury can occur because, as they state, “hyperoxemia appears to produce cellular injury through increased production of reactive oxygen intermediates such as super-oxide anion, the hydroxyl radical, and hydrogen peroxide.⁵”

When dealing with patients who suffer from an MI, it is important to note the cardiac function and how much damage has occurred. Many studies view the mortality rate, however, another study specifically looks at the wall-motion score index (WMSI), left ventricular ejection fraction through echocardiography, and the N-terminal pro-brain natriuretic peptide (NT-proBNP) levels at the initial visit and then again six months later.⁶ The patients were assessed through echocardiography between day two and day three after the catheterization and again six months later.⁶ In this study, the use of oxygen showed no significant differences in patients in regards to their WMSI and left ventricular function six months after the event and found it safe to withhold oxygen therapy in patients who present normoxic prior to catheterization.⁶

Even with significant, evidence-based data, it is hard to change practice. Nursing students have been hammered with the acronym MONA.⁵ It was stated that “physicians revealed that 96% of them administered supplemental oxygen to their patients with AMI.⁵” With generations of nurses practicing MONA, this would account for almost 100 percent of nurses. It is important for current nurses to know best practice so that they can prevent further injuries and decrease mortality. This can be seen widespread through the hospital. It was found that in one hospital that 22 percent of patients in an ICU were found to have hyperoxia.⁷ With hyperoxia being such a potent vasoconstrictor to coronary circulation, it can be related to a greater infarct.⁷

Patients will continue to seek medical attention for chest pain and symptoms that resemble an MI. It is crucial that not only are the symptoms treated but that the patients are cared for to the best of the medical staff’s abilities and with appropriate resources. Patients come to healthcare facilities to be helped, not harmed. It is important for the entire medical community to keep up with evidence-based practices and to continually educate each other, as well as our patients. If patients and families feel uncomfortable seeking medical attention it can be detrimental to their health. Even though there are certain practices that have been passed on from generation to generation, it is imperative that the best practice becomes a culture change to ensure that the patients and their families are in safe hands.

[akulahawkRN, ADN, RN, EMT-P]

The idea that supplemental oxygen can cause damage in normoxic patients has been around for at least 5, probably more like 10 years or more. I very much agree that it is very difficult to change practices when MONA has been beaten into Nursing and EMS providers for decades. Hyperoxia is also known to cause damage in stroke patients too.

At my first job in an ED, I routinely did NOT apply oxygen to normoxic patients precisely because I knew that hyperoxia causes more damage and in normoxic patients, the patient's body is receiving all the oxygen it really needs. IMHO, about the only time one should be considering hyperoxygenating normoxic patients is in those situations where the patient could benefit from being in a hyperbaric chamber. Even then you have to be very wary about oxygen as it can become quite toxic when under pressure.

[capsulcn]

Excessive oxygen is toxic！

[ShadowNurse]

This is very informative and good to know. It makes sense thinking about what we know about oxidative stress. We can just have a new acronym like NAM.

[RobbiRN, RN]

Excellent article. I found it particularly interesting that the definition of MI you quoted said "lack of blood-flow" instead of "lack of oxygen" as definitions have included in the past. The goal is to achieve normal oxygen levels, and we've learned we have to pay attention to deviations in either direction. But a lack of oxygen is still inherently more lethal.

[Horseshoe, BSN, RN]

Thanks for writing an article that doesn't read more like the opening chapter of a dimestore novel.

I'm more than a decade out of cardiac care-this is something I haven't kept up with, so I appreciate the information.

[Horseshoe, BSN, RN]

20 hours ago, akulahawkRN said:

The idea that supplemental oxygen can cause damage in normoxic patients has been around for at least 5, probably more like 10 years or more. I very much agree that it is very difficult to change practices when MONA has been beaten into Nursing and EMS providers for decades. Hyperoxia is also known to cause damage in stroke patients too.

I only recently learned about reperfusion syndrome and hyperoxia in stroke patients, when my father had a devastating ischemic stroke. I've been doing endo and OR for the past decade. I had not known that MONA had fallen out of favor.

That's why I love AN. I learn something every day. It's not just a venting web site.

[osceteacher]

Interesting, MONA is not something I've heard of in the UK. We have Clopidogrel for ACS management alongside Aspirin.

I do see NICE say you CAN use oxygen but there aren't any mandatory instructions to do so.

[CKPM2RN, ASN, EMT-P]

It has been practice in my area for a while now (7-ish years?) that we only apply oxygen to a stemi or any medical condition only if the patient is experiencing low sats and/or dyspnea. Oxygen is a tool in the toolbox. You don't have to use every tool every time.

[akulahawkRN, ADN, RN, EMT-P]

On 4/25/2019 at 7:19 AM, RobbiRN said:

Excellent article. I found it particularly interesting that the definition of MI you quoted said "lack of blood-flow" instead of "lack of oxygen" as definitions have included in the past. The goal is to achieve normal oxygen levels, and we've learned we have to pay attention to deviations in either direction. But a lack of oxygen is still inherently more lethal.

Lack of oxygen in hypoxic patients is going to be "inherently more lethal" but in the normoxic patient, the patient isn't hypoxic. You don't have flood MI patients with oxygen, you just have to keep their SpO2 levels between 94% and 99%. People that do hyperbaric medicine have known for a very long time that oxygen can be quite toxic to the body. That being said, hyperbaric oxygen can also be beneficial but those situations are very specific.

Mixed gas divers are probably about the most attuned to oxygen levels as nearly anyone I've ever met... but I digress.

What I've seen over the years is that it appears that simply keeping patients between 94% and 99% is pretty much the Goldilocks zone. Do what you must to achieve that. Ventilation is yet a different, but related beast.

[akulahawkRN, ADN, RN, EMT-P]

On 4/27/2019 at 9:29 AM, CKPM2RN said:

It has been practice in my area for a while now (7-ish years?) that we only apply oxygen to a stemi or any medical condition only if the patient is experiencing low sats and/or dyspnea. Oxygen is a tool in the toolbox. You don't have to use every tool every time.

Be ever so thankful that your area practices this. Other places aren't so eager to follow that and are very resistant to change. I'd be quite surprised if some of this resistance has to do with lawsuit avoidance because "withholding" oxygen in the normoxic patient isn't exactly considered standard practice. At least not yet.