NEW YORK (AP) — The call comes over the emergency-room loudspeakers: Sick patient. Everyone needed.

The patient is struggling to breathe, his blood-oxygen level a life-threatening 50%. Another presumed coronavirus case. Another human being whom Dr. Joseph Habboushe and his colleagues will try to save and get to a hospital bed for more care.

A seventh-generation physician who co-founded an online medical reference called MDCalc, the 44-year-old Habboushe has dug into the challenge of treating a new disease.

“It feels very appropriate that I get to be on the front lines and try to fight this war,” he says. “We’re all in this together, and we’re all in with our patients.”

But he's not immune to the dread. The fear that he or his colleagues may fall ill. The fact that "we don’t know our enemy, really.”

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The Associated Press followed 10 New York City residents on Monday, April 6, as they tried to survive another day in the city assailed by the new coronavirus. For more, read 24 Hours: The Fight for New York.

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Heading a coronavirus cases-only team at a Manhattan hospital that declined to be identified, Habboushe sees about 25 patients this Monday — fewer than in some recent days, but some are very sick. One was already on a ventilator when he arrived at 7:45 a.m., and her blood pressure was falling dangerously low.

Striking the right balance between boosting her blood pressure and keeping her sedated for the breathing machine proves to be the morning's most demanding problem. But the team finds a solution, and the woman's condition stabilizes.

Then the man with the extremely low oxygen level arrives.

A ventilator is available, but some doctors are now looking to other techniques, when possible. Some hospitals have reported unusually high death rates for coronavirus patients on breathing machines, though information is still emerging and limited.

Habboushe and his team try other means of giving the patient oxygen, but his levels remain low. The team turns him onto his stomach, a move that can sometimes help.

A half-hour later, the man's oxygen level is at a normal 95%. It’s too soon to say how he will ultimately fare, but the picture is much brighter.

Habboushe and his team don't end up putting anyone on a ventilator today. And all the patients survive, at least for now.

Still, the reflections of a doctor in the thick of the coronavirus crisis are a “bit of a roller-coaster,” and it keeps running into the night.

“It’s important that we focus on the positive and we focus on the increasing discoveries and ... finding ways to help these patients,” he says. “If I don’t do that, I just totally lose sight of what drives me every day.”