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Supplemental high-flow oxygen not beneficial for suspected ACS
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PARIS — Among patients with suspected acute coronary syndromes, new data from the NZOTACS trial show no difference in 30-day mortality for those treated with a high-oxygen protocol or a more conservative protocol that recommended limited oxygen.
The large, cluster-randomized, crossover trial included nearly 41,000 patients presenting with suspected or confirmed ACS in ambulances and hospitals across New Zealand over 2 years.
Researchers compared two oxygen protocols as part of routine care. The high-oxygen protocol recommended high-flow oxygen at 6 L to 8 L per minute for ischemic chest pain or ECG changes, irrespective of the blood oxygen saturation level; oxygen was stopped when clinical evidence of myocardial ischemia resolved. The low-oxygen protocol recommended oxygen only if the oxygen saturation level was below 90%, with a target of reaching a maximum saturation of 94%. Four geographic regions in New Zealand, including 24 hospitals, used both oxygen protocols for 12 months each in randomly allocated sequences.
The primary endpoint of 30-day mortality was 3.02% with the high-oxygen protocol compared with 3.12% with the low-oxygen protocol (OR = 0.97; 95% CI, 0.86-1.08), Ralph Stewart, MD, with Green Lane Cardiovascular Service at Auckland City Hospital in New Zealand, said while presenting the data during a Hot Line Session at the European Society of Cardiology Congress.
However, the high-oxygen strategy appeared beneficial in a prespecified subgroup of patients with STEMI as the final diagnosis, with a 30-day mortality rate of 8.8% compared with 10.6% with the low-oxygen strategy (OR = 0.81; 95% CI, 0.66-1). No difference in 30-day mortality emerged when the researchers evaluated this outcome in those with non-STEMI or no ACS as the final diagnoses, Stewart said.
The NZOTACS researchers also examined the effect of oxygen based on normal or reduced oxygen saturation, by looking at the first oxygen saturation level when the ambulance arrived. Patients with an oxygen saturation level above 95% — which Stewart said accounted for nearly 90% of the study population — had a similar mortality rate with the high- or low-oxygen protocol (2.1% vs. 1.9%, respectively). In those with a lower-than-normal oxygen saturation (< 95%) at baseline, mortality was substantially higher, he said, at 10.1% in the high-oxygen protocol group vs. 11.1% in the low-oxygen protocol group.
“Patients with suspected ACS who have a normal oxygen saturation level are very unlikely to benefit from high-flow oxygen, but there appears to be no harm,” Stewart said during the presentation. “It is possible that high-flow oxygen improves outcomes for patients with a lower-than-normal oxygen saturation than above the current recommended guideline and [those] with ST-elevation MI, but this could not be absolutely confirmed from this study.”
NZOTACS enrolled all patients presenting with suspected ACS during the study period who were in the All NZ Acute Coronary Syndrome – Quality Improvement Registry (n = 19,566), a hospital-based registry that includes 98% of ACS patients who have coronary angiography, with or without PCI, and/or the Ambulance Acute Coronary Syndromes Care Pathway (n = 29,401), an electronic ambulance record used by a system that services approximately 90% of the New Zealand population.
In total, 20,304 patients received the high-oxygen protocol and 20,568 received the low-oxygen protocol in ambulances, EDs, cardiac catheterization labs and/or acute cardiac care units.
The mean age of the patients was 66 years and 42% were women. The final diagnosis was STEMI in 10% of patients in both protocol groups, non-STEMI in 25% and unstable angina in 8%. In about 47% of patients, the final diagnosis was not ACS. In 9%, the researchers could not determine the diagnosis, according to Stewart.
In other results, protocol adherence was better for the low-oxygen protocol, which Stewart said “reflected clinicians deciding that they wouldn’t use the [high-oxygen] protocol because they thought that high oxygen was harmful, even though the patient had ischemic chest pain.”
The researchers conducted NZOTACS because the role of supplemental oxygen in patients with ACS has been uncertain.
“Oxygen has been used in the management of patients with acute MI for more than 50 years, but there is no study that shows it is beneficial. Some studies show it could be harmful. The current ESC guidelines indicate that oxygen should be used when saturation is below 90%, but not above,” Stewart said during the presentation.
The new NZOTACS data come on the heels of the DETO2X-AMI study, presented at ESC Congress 2017, which found routine supplemental oxygen did not reduce 1-year all-cause mortality in patients with suspected MI who did not have hypoxemia. Additionally, a meta-analysis of eight randomized controlled trials published in Heart in 2018 found no important clinical benefits of supplemental oxygen therapy in this population.
“I believe, at this stage, in patients with suspected ACS who do not have hypoxemia at baseline, routine oxygen therapy provides no benefit and therefore should not be given,” Robin Hofmann, MD, PhD, of Karolinska Institute, department of clinical science and education, division of cardiology, said during a discussion of the trial. “Concerning subgroups and the ideal cutoff to initiate oxygen therapy, more data from present or new trials are needed to draw robust conclusions.” – by Katie Kalvaitis
References:
Stewart R, et al. Hot Line Session 2. Presented at: European Society of Cardiology Congress; Aug. 31-Sept. 4, 2019; Paris.
Sepehrvand N, et al. Heart. 2018;doi:10.1136/heartjnl-2018-313089.
Disclosures: Stewart and Hofmann report no relevant financial disclosures.
Perspective
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Robert A. Harrington, MD
This is a trial that represents those 100 clinical questions that we all have: does this actually work? It’s never been studied, It’s always been assumed that it works. Oxygen for somebody having a heart attack was that sort of thing. We just assumed that it worked. There were some studies that came out a few years ago that not only suggested that it might not add value, but that it might add harm. There was this real conundrum. New Zealand is a country that has been able over the last several years to mobilize their country, connecting electronic health records and registry data to actually do country-wide clinical trials, While the oxygen question itself is kind of interesting, what’s really interesting is how New Zealand has created this mechanism that’s going to allow them to test a lot of what clinicians want to know every day but has never been studied. I’m excited about that one.
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