You are about to begin dental treatment on your healthy 65-year-old male patient when he suddenly develops severe chest pain. You suspect he is having an acute myocardial infarction and immediately call 911. You then refer back to the treatment algorithm, MONA, an acronym (morphine, oxygen, nitroglycerin and aspirin) used in the management of patients with a suspected acute myocardial infarction. There is, however, growing evidence suggesting that MONA may need to be modified in order to more appropriately manage these patients. In this article, we will be reviewing the current literature around the use of supplemental oxygen in a suspected acute myocardial infarction.
This first question we need to ask is why should we administer supplemental oxygen during an acute myocardial infarction? During myocardial ischaemia, there is a reduction of blood flow to the myocardium, resulting in reduced oxygen supply to the heart. The end result is myocardial infarction (i.e. death of the cardiac myocytes). It is thought that supplemental oxygen can improve the oxygenation of the ischemic heart tissue and in turn reduce the size of the infarct. 1,2
Nevertheless, it is important to remember that oxygen is a drug and just like any drug we prescribe to our patients, it can have possible adverse side effects. This leads to our next question: can oxygen administration during an acute myocardial infarction be harmful? There have been studies that suggest supplemental oxygen may have potential adverse physiologic effects, including a decrease in cardiac output and coronary blood flow and an increase in coronary vascular resistance (through the production of reactive oxygen species). In turn, there is a reduction in oxygen delivery to the myocardium resulting in reperfusion injury. 3
The next question we need to ask is should we administer oxygen to patients who have a suspected myocardial infarction (chest pain) but have normal oxygen saturation (and otherwise look well)? We will answer this by reviewing a randomized clinical trial by Hoffman et al. (2017) entitled, “Oxygen Therapy in Suspected Acute Myocardial Infarction”, also known as the DETO2X-AMI trial. Patients 30 years of age and older, who had a suspected acute myocardial infarction for less than six hours and an oxygen saturation of 90% or higher were included in the study. They were randomized into one of two groups. One group received oxygen therapy and the other group remained on room air. The primary end point of this study was death from any cause at one-year post-intervention. The secondary end point was death from any cause within 30 days. This is clinically important since the study’s primary and secondary end points were patient-centred. The authors concluded that the routine use of supplemental oxygen did not reduce one-year mortality rates in patients with a suspected myocardial infarction who were not hypoxemic. It is important to note that the study did not show any signs of harm associated with the use of supplemental oxygen in patients with a suspected myocardial infarction. 4
The results of the Hoffman study (2017) are further supported by a meta-analysis published by Li et al. (2018) which concluded that supplemental oxygen did not benefit patients with acute myocardial infarction who were normoxaemic. 5 In addition, the current Advanced Cardiac Life Support guidelines recommend that for a patient with symptoms suggestive of ischaemia or infarction, one should administer supplemental oxygen if the patient’s oxygen saturation is less than 90%. 6 We can therefore conclude that there does not appear to be any benefit in supplemental oxygen administration in patients with an acute myocardial infarction with an oxygen saturation of 90% or higher.
In summary: How can we apply this information to our current practice in a dental setting?
1. If a pulse oximeter is available and the patient’s oxygen saturation is 90% or higher, you may consider withholding supplemental oxygen therapy.
2. If a pulse oximeter is available and the patient’s oxygen saturation is less than 90%, or if a pulse oximeter is not available and the patient looks unwell (pale, cyanotic, in respiratory distress), then provide supplemental oxygen. OH
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Acknowledgements
Dr. Rachel Tobis would like to thank Dr. Robert Matsui and Dr. Carilynne Yarascavitch for their support in providing additional information and the references cited in this article.
References
- Madias JE, Madias NE, Hood WB, Jr. Precordial ST-segment mapping. 2. Effects of oxygen inhalation on ischemic injury in patients with acute myocardial infarction. Circulation. 1976;53(3):411-7.
- Maroko PR, Radvany P, Braunwald E, Hale SL. Reduction of infarct size by oxygen inhalation following acute coronary occlusion. Circulation. 1975;52(3):360-8.
- Cornet AD, Kooter AJ, Peters MJ, Smulders YM. The potential harm of oxygen therapy in medical emergencies. Crit Care. 2013;17(2):313.
- Hofmann R, James SK, Jernberg T, Lindahl B, Erlinge D, Witt N, et al. Oxygen Therapy in Suspected Acute Myocardial Infarction. N Engl J Med. 2017;377(13):1240-9.
- Li WF, Huang YQ, Feng YQ. Oxygen therapy for patients with acute myocardial infarction: a meta-analysis of randomized controlled clinical trials. Coron Artery Dis. 2018;29(8):652-6.
- Heart and Stroke Foundation. Advanced Cardiovascular LIfe Support, Provider Manual. Canada 2015.
About the Author
Dr. Rachel Tobis is in her third year of a dental anaesthesia residency at the Faculty of Dentistry at the University of Toronto.
