Question

Studies have shown that the use of oxygen for the treatment of Acute Coronary Syndrome is now detrimental to the myocardium and may worsen patient outcomes. Discuss the evidence that brought about changes to paramedic clinical practice.

Answer 1

AN article by Monish.SR and Arun M. from Department of Cardiac Anesthesiology, Sir Ganga Ram Hospital, New Delhi, India on "Oxygen supplementation in acute myocardial infarction: To be or not to be?" speaks of a case scenario about a client admitted in Intensive care unit with severe chest pain. Electrocardiogram showed ST elevation in anterior leads suggestive of anterior wall ST elevation myocardial infarction (STEMI).Admist their treatment the question on the positive and negative affect of Oxygen administration was discussed which is to give oxygen in such situations to improve the oxygenation of the ischemic myocardial tissue and decrease ischemic pain however recent intriguing evidences have challenged this conventional thinking as oxygen may be harmful considering the mechanism such as paradoxical effect of oxygen in decreasing coronary artery blood flow and increasing coronary vascular resistance that can be measured by intracoronary Doppler ultrasonography,decrease in cardiac output and stroke volume,hyperoxia causing increased vascular resistance, and reperfusion injury due to increased oxygen free radicals.

The American Heart Association Guidelines for Cardiopulmonary Resuscitation (CPR) and Emergency Cardiovascular Care recommends oxygen in patients with dyspnea, hypoxemic, or with signs of heart failure and shock, based on monitoring of oxyhemoglobin saturation, to ?94% (Class I, LOE C).However, their evidence on support of oxygen use in uncomplicated acute coronary syndromes is inadequate.

A randomized, controlled, multicenter trial with the aim of comparing oxygen supplementation (6–8 L/min) with no oxygen in STEMI patients with oxygen saturation in the normal range pulse oximetry saturation >94%.Study showed a significant 25% increase in creatine kinase which is suggestive of increased myocardial injury and cardiovascular magnetic resonance at 6 months suggestive of larger infarction size with oxygen therapy. Although mortality was similar in both groups, significant increases in recurrent MI and arrhythmias were observed in the oxygen groupEven though AVOID Study used higher oxygen flow 6–8 L/min (more than usual clinical practice) and study was not powered for hard clinical end points, this Air Verses Oxygen In myocardial infarction study (AVOID Study) trial would really question the current practice of oxygen supplementation to all patients with acute myocardial ischemia and definitely to those with normoxia suggested routine oxygen supplementation to AMI patients from the ambulance through to the recovery room might actually be hurting their hearts.

Another reference from NICE National Institute for health and care excellence in their article "Oxygen therapy for acute ST-segment-elevation myocardial infarction " suggest that oxygen therapy could be associated with an increase in muscle damage during STEMI. This evidence supports NICE guidance that oxygen should not be routinely administered to people with suspected STEMI.  

Considering the weightage on the advantage and disasvantage of oxygen administration implementation of changes in paramedic clinical practice can be necessary.