To communicate with Zhang, the patients would write down questions, asking if they would recover, or when they could be discharged. Sometimes it would be simple requests to contact family or asking for something to eat. Zhang always tried his best to fulfill the patients' needs.

Li Zenghui, 32, an ICU nurse with the PUMCH team, arrived in Wuhan on Feb 7.

The following day, as she was entering the ward for the first time, a bit nervous, she saw Zhang walking out after a typically long shift.

"I saw the skin on both sides of his nose scraped with blood, because he was too skinny and the face mask was too tight," Li recalls.

Li remembers that the first month in Wuhan was stressful for both doctors and nurses, as seriously ill COVID-19 patients kept coming, and there was not even time for them to indulge in sentiment for the patients they were unable to save.

"In those first few days, there was a constant line of ambulances in front of the hospital waiting to send patients in," Li recalls.

She recalls that, when they were working in Wuhan, nurses could leave after a four-hour shift, while the doctors might have to extend their six-hour shift until the next one ended if they were in the middle of an operation when the changeover took place.

Zhang once worked nearly 12 hours straight. He remembers one particular instance, after a long, busy shift, when he was leaving the ward and one seriously ill patient was being wheeled in, but he decided not to stay.

"I felt suffocated by my protective gear and I decided to leave. Otherwise I might have collapsed, and my colleagues all understood. If my body was in a better condition, I would have stayed," Zhang says.