When an 87-year-old Californian man was wheeled into an operating room just outside Phoenix last year, the pandemic was at its height and medical protocols were being upended across the country.

A case like his would normally have required 14 or more bags of fluids to be pumped into him, but now that posed a problem.

Had he been infected with the coronavirus, tiny aerosol droplets could have escaped and infected staff, so the operating team had adopted new procedures that reduced the effectiveness of the treatment but used fewer liquids.