The latest intervention from Donald Trump’s medical team has been to put the president on dexamethasone, a steroid that is proven, thanks to the UK’s Recovery trial, to benefit Covid-19 patients who are having breathing difficulties.

But the decision to administer the steroid now has only added to the confusion surrounding the president’s state of health. Normally, dexamethasone is reserved for patients who have been ill for at least a week and whose oxygen levels are low.

Peter Openshaw, a professor of experimental medicine at Imperial College London, and a member of the UK government’s New and Emerging Respiratory Virus Threats Advisory Group, said: “It would be unusual to be starting steroids with a relatively short duration of illness. It’s normally reserved for people who have had symptoms for a week or more and who are going into respiratory failure.”

Doctors said on Sunday that on Friday and Saturday Trump’s oxygen saturation levels had twice dipped below 94% – the usual range being 95 to 100%. But in answer to a question about whether the level ever fell below 90%, the White House physician, Sean Conley, said it had never reached the low 80s.