A systematic review and meta-analysis of published studies from three continents shows overall mortality of Covid-19 patients in intensive care units has fallen from almost 60% at the end of March to 42% at the end of May – a relative decrease of one third.

The review, led by the University of Bristol and Royal United Hospitals Bath NHS Trust and published in Anaesthesia, a journal of the Association of Anaesthetists, also shows ICU mortality for the disease is similar across the three continents included: Europe, Asia and North America.

Review lead author Professor Tim Cook said: “The important message is that, as the pandemic has progressed and various factors combine, survival of patients admitted to ICU has significantly improved. There were no significant effects of geographical location, but reported ICU mortality fell over time. Optimistically, as the pandemic progresses, we may be coping better with Covid-19.

“The in-ICU mortality from Covid-19, at around 40%, remains almost twice that seen in ICU admissions with other viral pneumonias, at 22%.”

There are several possible explanations for the findings regarding decreasing ICU mortality over time.

Cook said: “It may reflect the rapid learning that has taken place on a global scale due to 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.”

The findings are also likely to reflect the fact that long ICU stays, for example, due slow weaning from a ventilator, take time to be reflected in the data. Critical illness associated with Covid-19 can last for long periods, with approximately 20% of UK ICU admissions lasting more than 28 days, and 9% more than 42 days.

The ICU mortality did not differ significantly across continents despite some evidence of variations in admission criteria, treatments delivered and the thresholds for their application. This is consistent with research findings up until the end of May suggesting that no specific therapy reduces ICU mortality. In the last few weeks dexamethasone has been found to have significant benefit and there is hope this will improve survival further.

Date published: July 16, 2020

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