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No clear benefit from conservative oxygen in mechanical ventilation


 

FROM NEJM

More conservative oxygen therapy during mechanical ventilation in intensive care does not appear to increase the number of ventilator-free days or reduce mortality, according to a study published online in the New England Journal of Medicine.

Diane Mackle of the Medical Research Institute of New Zealand and her co-authors wrote that hyperoxemia in adults undergoing mechanical ventilation has been associated with increased mortality, as well as fewer days free of ventilation, but there was a lack of data to guide oxygen administration.

In a parallel-group trial, 1,000 adults who were expected to require mechanical ventilation – with an intention-to-treat population of 965 – were randomized either to conservative oxygen therapy or usual therapy. For the conservative therapy, the upper limit of the pulse oximetry alarm would sound when levels reached 97% and the F102 was decreased to 0.21 if the pulse oximetry was above the acceptable lower limit, while usual therapy involved no specific limiting measures. In both groups, the default lower limit for oxygen saturation was 90%.

At day 28 after ventilation, there was no significant difference between the conservative and usual care groups in the number of ventilator-free days (21.3 days vs. 22.1 days). The patients in the conservative oxygen group spent a median of 29 hours receiving an F102 level of 0.21, compared with 1 hour in the usual care group.

The mortality rate at day 180 was 35.7% in the conservative oxygen group, and 34.5% in the usual-oxygen group (HR 1.05, 95% CI 0.85 – 1.30). Researchers also saw no differences between the two groups in paid employment and cognitive function.

In patients with suspected hypoxic-ischemic encephalopathy between-group differences were apparent; At day 28, those in the conservative-oxygen group had a median of 21.1 ventilator-free days, compared with none in the usual-oxygen group. The usual-oxygen group also had a higher 180-day mortality rate than those in the conservative-oxygen group (43% vs. 59%).

“Our data are suggestive of a possible benefit of conservative oxygen therapy in patients with suspected hypoxic-ischemic encephalopathy,” the authors wrote. “It is biologically plausible that conservative oxygen therapy reduces the incidence of secondary brain damage after resuscitation from cardiac arrest, and observational data suggest that exposure to hyperoxemia in such patients may be harmful.”

The authors noted that their trial did not rule out the possibility of benefit or harm had they used a more liberal oxygen regimen in their usual-care group, and that different conservative regimens might also have achieved different outcomes.

The study was funded by the New Zealand Health Research Council. Six authors declared research support for the trial from the study funder, and two declared unrelated research grants from private industry. No other conflicts of interest were declared.

SOURCE: Mackle D et al. NJEM 2019, October 14. DOI:10.1056/NEJMoa1903297.

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