Some people may have coronavirus with only mild symptoms, while others may never even realise they had it.

But for others, Covid-19 can be a life-threatening condition which needs serious hospital treatment.

Some patients will end up in intensive care, where specialist teams will provide round-the-clock care.

On Monday evening, Downing Street confirmed Prime Minister Boris Johnson had been moved to intensive care after his coronavirus symptoms worsened. The Press Association news agency reported he was conscious when he was moved to intensive care at about 7pm, as a precaution should he require ventilation to aid his recovery. You can follow live updates here.

Here, we look at what generally happens when a coronavirus patient is in intensive care.

The NHS describes intensive care units (ICUs) as specialist hospital wards which provide treatment and monitoring for people who are very ill.

They're staffed with specially trained healthcare professionals and contain sophisticated monitoring equipment.

ICUs are also sometimes called critical care units (CCUs) or intensive therapy units (ITUs).

When is intensive care needed?

Intensive care is generally needed if someone is seriously ill and requires intensive treatment and close monitoring, or if they're having surgery and intensive care can help them recover.

Most people in an ICU have problems with one or more organs. For example, they may be unable to breathe on their own.

There are many different conditions and situations that can mean someone needs intensive care.

What about coronavirus patients in ICU?

Dr David Hepburn, ICU consultant at the Royal Gwent Hospital in Newport, has outlined the reality of what it's like to be in intensive care as a coronavirus patient.

Referring to patients whose treatment involved being put on ventilators, he told Channel 4 News: "The patients themselves, on the whole, are unconscious. We anaesthetise most people on ventilators just because it's very unpleasant having a foot-long plastic tube through your mouth, down the back of your tongue, and into your upper airway.

"Most people will need some degree of sedation to tolerate that.

"It also means they will synchronise better with the ventilators, they're not fighting the ventilators, they'll allow the ventilators to do their job.

"The vast majority of patients are fast asleep at the moment, mainly for their comfort and also to facilitate their care."

In the interview last week, he said no visitors were currently being permitted as it was "logistically impossible".

"It's incredibly difficult. We are updating people as much as we can, we've got dedicated people who are phoning and updating relatives every day, we're also using email and we're able to use video calling.

"But it's a poor facsimile of actually sitting down in a room with proper human contact, to be able to give someone a hug, or offer them a hand if they're upset.

"We are looking at potentially finding a way to allow family members to come in, accepting the risk and wearing full PPE - it's the last thing we want to deny anyone, time with their family member if they're going to die, but the practicalities of that, we haven't ironed out yet."

The critical care consultant, who himself has recovered from Covid-19, outlined how full their ICU currently is, with the virus yet to reach its peak in Wales.

He told Channel 4 last week there were 16 ventilated patients in the intensive care unit at that time, leading them to "completely run out of space, so we've taken over theatre recovery, and we've got a further eight there".

By the end of last Friday, April 3, he was expecting that area to be full, taking them up to 25 patients.

"We have another area prepared, which is the old high dependency unit in coronary care, and we can fit a further 22 patients in that area."

Asked about what it's like inside ICU, he said it's "controlled chaos".

"The difference is everybody is desperately unwell, everybody is on a ventilator, so the severity of illness that we're seeing is very high, the staff are all wearing full PPEs.

"Everybody is aware if the severity of the situation.

"At the moment we've got sufficient capacity to deal with the demand but as weeks go on, if we don't see a slowing down in the infection rate and we don't flatten the curve then we are going to start running out of space, and that's when very difficult decisions are going to have to be made.

"I hope to God I don't have to do that, but it may happen, and we've seen it happen in Italy as well."

He said the hospital was expecting much older people to be affected by Covid-19.

"The patterns of illness we've seen in Gwent - and I can't speak for anywhere else - is much younger patients than we were expecting," he said.

"When the reports first started coming out of Wuhan we were led to believe that this was something that was particularly dangerous for the more elderly patients.

"But I would say that all the patients we have in intensive care are in their 50s or younger at the moment. It surprised us - our youngest patient is in her early 20s.

"There are a lot of patients who do not have any pre-existing medical conditions."

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What does intensive care involve?

The NHS said that patients on an ICU will be looked after closely by a team of staff and will be connected to equipment by a number of tubes, wires and cables.

There will normally be one nurse for every one or two patients.

This equipment is used to monitor their health and support their bodily functions until they recover.

Equipment that may be used on an ICU includes: 

Someone in an ICU will often be on pain-reducing medicine and medicine that makes them drowsy as some of the equipment used can be uncomfortable.

What happens after intensive care?

If a patient recovers and no longer needs intensive care, they can be transferred to a different ward to continue their recovery before eventually going home.

Some people may leave the ICU after a few days. However, others may need to stay for months.

Dr David Hepburn added: "One more thing: if you end up on ITU it’s a life-changing experience.

"It carries a huge cost even if you do get better. As our patients wake up, they are so weak they can’t sit unaided, many can’t lift their arms off the bed due to profound weakness.

"They need to be taught to walk again, breathe again, and have problems with speech and swallowing. Some have post traumatic stress, body image and cognitive problems.

"They get better in time but it may take a year and needs an army of physiotherapy, speech and language, psychology and nursing staff to facilitate this. The few weeks on a ventilator are a small footnote in the whole process."