High-flow oxygen offers no benefit in ACS

High-flow oxygen is not associated with an increase or a decrease in 30-day mortality, suggesting no benefit in most patients presenting with a suspected acute coronary syndrome (ACS), reports a New Zealand study.

“The result supports current clinical practice guidelines, which recommend that oxygen is not given to patients with suspected ACS who have a normal oxygen saturation (SpO2),” the researchers said. [Circulation 2014;130:2354-2359; Eur Heart J 2018;39:119-177; Circulation 2013;127:e362-425; Eur Heart J 2016;37:267-315]

“However, the study neither confirmed nor excluded the possibility of a small benefit from supplementary oxygen in patients presenting with ST elevation myocardial infarction (STEMI),” they added.

This pragmatic, cluster randomized, crossover trial examined 40,872 patients with suspected or confirmed ACS included in the All New Zealand Acute Coronary Syndrome Quality Improvement registry or ambulance ACS pathway during the study periods. A total of 20,304 patients were managed using the high-oxygen protocol and 20,568 using the low-oxygen protocol.

Four geographical regions in New Zealand were randomly assigned to each of two oxygen protocols in 6-month blocks over 2 years. The high-oxygen protocol recommended oxygen at 6–8 L/min by face mask for ischaemic symptoms or electrocardiographic changes, regardless of the transcapillary SpO2. The low-oxygen protocol, on the other hand, recommended oxygen only if SpO2 was <90 percent, with a target SpO2 <95 percent.

Personal and clinical characteristics of patients managed under both protocols were well matched. For those with suspected ACS, 30-day mortality was 3.0 percent (n=613) for the high-oxygen group and 3.1 percent (n=642) for the low-oxygen group (odds ratio [OR], 0.97, 95 percent confidence interval [CI], 0.86–1.08). [BMJ 2021;372:n355]

For 4,159 (10 percent) patients with STEMI, 30-day mortality was 8.8 percent (n=178) and 10.6 percent (n=225) for the high- and low-oxygen groups, respectively (OR, 0.81, 95 percent CI, 0.66–1.00). For 10,218 (25 percent) non-STEMI patients, the rates were 3.6 percent (n=187) and 3.5 percent (n=176), respectively (OR, 1.05, 95 percent CI, 0.85–1.29).

These findings support those from previous studies, suggesting that high-flow oxygen does not confer benefits to most patients with presumed ischaemic chest pain and a normal oxygen saturation level. [N Engl J Med 2017;377:1240-1249; Heart 2018;104:1691-1698; Circulation 2015;131:2143-2150]

“Because oxygen is widely used, it is important to determine that it is not associated with harm,” the researchers said. “In the current study, as in real world use, oxygen was given to patients with suspected ACS before the diagnosis was confirmed, with the knowledge that many patients will not have a final diagnosis of ACS.” [J Emerg Med 2005;29:383-390]

Current clinical practice guidelines recommend giving oxygen to patients with STEMI or non-STEMI when the SpO2 is <94 percent or <90 percent despite little evidence from randomized trials. [Circulation 2014;130:2354-2394; Eur Heart J 2018;39:119-177; Thorax 2017;72(Suppl 1):ii1-90; Circulation 2013;127:e362-425; Eur Heart J 2016;37:267-315]

“Low statistical power for modest but clinically important effects of oxygen is a limitation of the current and all previous studies,” the researchers said.