Clinical trials in cardiac emergencies
Should we refrain from the routine use of supplemental oxygen in cardiac emergencies, or are the considerations outlined above sufficiently outweighed by an intuitive impetus that supplemental oxygen is beneficial? Clinical trials addressing the question of whether oxygen should be administered during acute myocardial infarction are scarce. In 1976, a double-blind randomized controlled trial was performed in 200 consecutive patients (younger than 65 years old) who were admitted with suspected acute myocardial infarction [26]. Patients with CHF, chronic pulmonary disease, or breathlessness from any cause other than acute myocardial infarction were excluded. Patients were randomly assigned to receive either oxygen or compressed air at a flow rate of 6 L/minute for a total of 24 hours. The mean partial arterial oxygen tension (PaO2) was significantly higher in the group receiving oxygen. In that group, 9 out of 80 (11.3%) patients died as compared with 3 out of 77 (3.9%) in the compressed air group, corresponding with a relative mortality risk of 2.9 (95% confidence interval (CI) 0.8 to10.3, P = 0.08) [26]. A trial similar by design, but open-label, reported that 1 out of 58 (1.7%) patients died in the group treated with oxygen (4 L/minute) versus 0 out of 79 patients in the group receiving ambient air; however, the duration of oxygen exposure is not reported [27]. A recent Cochrane review meta-analyzed available studies on oxygen therapy in patients with acute myocardial infarction. Combining the two aforementioned studies generated a relative risk (RR) of mortality of 3.03 (95% CI 0.93 9.83, P = 0.06) [28].