Science and discoveries is about ‘questions’ and finding ‘answers’ and this has shaped our thoughts and has built the foundations of science as we know. But occasionally these very tenets are questioned as is the case with the present research on oxygen - the aroma of our life.

What is being questioned is fundamental treatment modality that have been in vogue for ages.. Inhalation of oxygen (O2) has been a part of the initial management of people suffering from a heart attack. But now doubt has been raised  about its efficacy and to know whether it does more harm than good.

Coronary Heart Disease (CHD) is one of the  major cause of death in all the countries  and lists among the top such causes. A heart attack (which is the common name for Myocardial Infarction or MI) occurs when the availability of blood and oxygen to a section of heart muscle becomes blocked. This is usually caused by a clot. Thus logically, supplemental oxygen which can be given by face mask or nasal cannula to a patient with MI will reverse the oxygen deprivation.

Concerns have however arisen about the use of oxygen. Oxygen may be biologically harmful, suggests studies. Contrary to what is expected O2 may reduce coronary artery blood flow; increase the resistance offered by coronary blood vessels. The heart’s efficiency (cardiac output) may hence fall. Oxygen free radicals may also add to the troubles. Conclusive evidence as to whether administration of oxygen diminishes an acute myocardial infarction is unavailable. In fact, the mentioned harms credited to O2 are not completely proven either.

Hence, most of the international guidelines for the treatment of patients still recommend oxygen. New research urges that this treatment is reassessed, owing to the ambiguity.

Randomized controlled trials of people with suspected or proven AMI (acute myocardial infarction), less than 24 hours after onset where the management was inhaled oxygen were compared to ones where air was used. A wide range of bibliographic databases were searched irrespective of their languages. Experts were also contacted.

The patient outcomes assessed were death, pain and other complications. Relative risk (RR) was used as a measure of effect.

The results were thus: 3 trials involving 387 patients were included in the study, 14 deaths occurred. The pooled Relative Risk of death was 2.88 (95% CI 0.88 to 9.39) in an intention-to-treat  analysis and 3.03 (95% CI 0.93 to 9.83) in patients with confirmed AMI. Though these results are suggestive of harm, the meager number of deaths recorded meant that this could be a chance occurrence. Pain was assessed by analgesic use. The pooled Relative Risk for the use of analgesics was 0.97 (95% CI 0.78 to 1.20).

Thus there is no conclusive evidence from randomized controlled trials to support the routine use of inhaled oxygen in patients with a heart attack. Mismatch still exists  between trial evidence suggestive of possible harm from routine oxygen use and recommendations for its use in clinical practice guidelines.

A definitive randomized controlled trial is therefore urgently required so as to reach a proper consensus.

Source: Cochrane Journal Club