Overall mortality of covid-19 patients in intensive care units (ICU) has fallen from 59.5% at the end of March to 41.6% at the end of May, a drop of almost a third, researchers have said.

The team from England carried out a systematic review and meta-analysis of published studies from Asia, Europe, and North America, and found that while mortality appeared to have declined, it was still “almost twice that seen in ICU admissions with other viral pneumonias, at 22%.”

The paper, published in Anaesthesia, included 24 observational studies with 10 150 adult patients identified from centres across three continents. There were reports of patients from China (eight studies), the US (six studies), France (two studies), Canada, Denmark, the Netherlands, Hong Kong, Italy, Singapore, Spain, and the UK (one study each).

The review’s primary outcome of measure was death in ICU as a proportion of completed ICU admissions, either through discharge from the ICU or death. It did not include patients still alive on ICU. Recruitment in these 24 studies was from 16 December 2019 to 28 May 2020, and only seven studies reported outcome data for all patients. In the rest, the proportion of patients discharged from ICU at the point of reporting varied from 24.5% to 97.2%.

In patients with completed ICU admissions with covid-19 infection, combined ICU mortality was 41.6% (95% confidence interval, 34.0% to 49.7%) for January to May. This is a notable drop from the 59.45% mortality reported for January to March, the researchers said.

About the decreasing mortality, the authors said, “It may reflect the rapid learning that has taken place on a global scale because of the prompt publication of clinical reports early in the pandemic. It may also be that ICU admission criteria have changed over time, for example, with greater pressure on ICUs early in the pandemic surge.”

But the researchers also noted that long ICU stays take time to be reflected in the data. They said this was especially important with covid-19, as around 20% of UK ICU admissions lasted more than 28 days, and 9% lasted more than 42 days.

“The message, however, is that as the pandemic has progressed and all these factors combine, survival of patients admitted to ICU with covid-19 has significantly improved,” they said.

Mortality did not differ significantly across continents, which the researchers said demonstrated that during the period studied there was no specific effective therapy.

This was before the dexamethasone results from the RECOVERY trial—which found that a low dose of the steroid reduced deaths in patients hospitalised with covid-19 who need ventilation.