President Donald Trump‘s oxygen levels raised concern Friday morning after they dropped to lower-than-normal levels. White House Chief of Staff Mark Meadows said Saturday night that he and White House physician Dr. Sean Conley were “really concerned” about Trump’s blood oxygen levels dropping so rapidly.

Doctors at Walter Reed National Military Medical Center, where Trump is being treated, said that the president had a high fever on Friday and there have been two separate incidents of his oxygen levels dropping — one Friday and one Saturday. Dr. Conley stated that Trump’s oxygen levels dropped to 93 percent at one point, which is below the 95 percent level that is considered the lower limit of the normal range.

Despite providing information that he was given supplemental oxygen for about an hour on Friday, Dr. Conley dodged questions regarding whether Trump received additional oxygen supplements on Saturday. The White House has since released an update in which Dr. Conley stated that Trump was off supplemental oxygen and his saturation levels were between a normal 96 percent and 98 percent all day.