Coronavirus and the disease it causes, Covid-19, have dominated the headlines. Yet the range of expectations and predictions of its impacts have been so wide as to make clear understanding almost impossible. This is perhaps inevitable when we grapple with a fast-moving and previously unknown illness. What is clear, is that as knowledge grows it has become evident that this has the potential to be one of the most fatal epidemics to have hit the world for a century, and it is rapidly increasing in prevalence in the UK.

I work as a doctor in an intensive care unit (ICU). It is a speciality (like anaesthesia its parent speciality) which most of the public have little understanding of unless they have required our services. What is in no doubt is that ICU sits at the centre of all that is necessary for keeping alive what may be a very large number of patients who will develop severe Covid-19.

ICU treats patients whose lives are at risk or whose organs have failed. Severe Covid-19 leads mostly to lung failure but also causes kidney and cardiovascular (heart and blood vessel) failure. All these are rapidly fatal without intense and prompt treatments only available in ICU. In simple terms, treatments include a ventilator taking over the patient’s breathing while the patient is anaesthetised (placed in an induced coma), a dialysis machine cleaning the blood and drugs or machines supporting the heart and blood pressure. The reality of care is, of course, considerably more complex and highly intensive.

So let’s look at some statistics: it is likely that more than 30% of the whole UK population will get Covid-19 – it may be as high as 60% in some estimates. Most will have no or mild illness but maybe one in seven will need hospital admission. Of patients in hospital up to one in five may need ICU care – that would be an unprecedented number of people admitted to ICU. As many as one in 50 of patients known to have Covid-19 may die from it.

Quick Guide What are coronavirus symptoms and should I go to a doctor? Show What is Covid-19? Covid-19 is caused by a member of the coronavirus family that has never been encountered before. Like other coronaviruses, it has come from animals. The World Health Organization (WHO) has declared it a pandemic. What are the symptoms this coronavirus causes? According to the WHO, the most common symptoms of Covid-19 are fever, tiredness and a dry cough. Some patients may also have a runny nose, sore throat, nasal congestion and aches and pains or diarrhoea. Some people report losing their sense of taste and/or smell. About 80% of people who get Covid-19 experience a mild case – about as serious as a regular cold – and recover without needing any special treatment. About one in six people, the WHO says, become seriously ill. The elderly and people with underlying medical problems like high blood pressure, heart problems or diabetes, or chronic respiratory conditions, are at a greater risk of serious illness from Covid-19. In the UK, the National health Service (NHS) has identified the specific symptoms to look for as experiencing either: a high temperature - you feel hot to touch on your chest or back

a new continuous cough - this means you’ve started coughing repeatedly As this is viral pneumonia, antibiotics are of no use. The antiviral drugs we have against flu will not work, and there is currently no vaccine. Recovery depends on the strength of the immune system. Should I go to the doctor if I have a cough? Medical advice varies around the world - with many countries imposing travel bans and lockdowns to try and prevent the spread of the virus. In many place people are being told to stay at home rather than visit a doctor of hospital in person. Check with your local authorities. In the UK, NHS advice is that anyone with symptoms should stay at home for at least 7 days. If you live with other people, they should stay at home for at least 14 days, to avoid spreading the infection outside the home.

ICU is a precious and scarce resource in terms of beds, staff and equipment. This is especially so in the UK. In 2012 the UK had about 4,100 critical care beds including ICU beds and “high dependency” beds which are a step down from full ICU care. Compared with other European countries the UK ranked 24th of 31 in terms of ICU beds per head of population and 29th of 31 for all hospital beds. Germany has approximately four times as many ICU beds per capita as the UK and the USA perhaps 10-fold as many. Data from 2017 suggest little change. Most UK ICUs therefore run at or above 90% occupancy and often can only admit new patients only by discharging others – even when workload is normal. Covid-19 will increase pressures not only because of weight of numbers but because intermediate treatments for pneumonia and lung failure are “aerosol-generating” (ie they risk spreading the disease) so cannot be used and early recourse to ICU is required.

Increased ICU demands equate to each ICU bed being needed for approximately 100 more patients than on average in the epidemic period – at least 10 times the normal throughput and equivalent to needing at least another 10 ICUs in the hospital during the epidemic. Of course, this demand will be in addition to, rather than instead of, normal workload as the illnesses that usually require ICU admission will not go away during the epidemic. In Wuhan, ICU capacity was increased by over 1,000 beds in two weeks by building a new hospital, but this is not possible in the UK.

Managing an ICU patient with Covid-19 is more complex than normal ICU care. Patients must be individually isolated. All staff must wear “personal protective equipment” (PPE), which consists of, as a minimum, a tight-fitting face mask, an extra gown, gloves, goggles and visor. PPE must be put on and taken off before and after patient contact and checked by a “buddy” colleague. Despite this scrupulous process in China two in every five early infections were acquired in hospital and two-thirds of these were healthcare workers, a significant number of whom then died. These demands slow down care, increase the number of staff needed and expose staff (and perhaps their families) to significant risk.

Patients in ICU have constant one-to-one nursing. Medical interventions are frequent, invasive and performed at extremely close proximity. Contact with body fluids is inevitable and common. But it is not only nurses and doctors who are at risk. Hospital cleaners will be required to be on hand at all times and rigorous cleaning is required between patients and after many procedures. Physiotherapists, dietitians, laboratory technicians and other medical specialists involved in care are also at risk. Keeping staff safe has implications beyond their welfare: skilled staff are a limited resource and if sickness rates are even moderate there will be major gaps in service.

The challenge from Covid-19 to ICU services in the UK is enormous and pressing. Throughout the UK, ICUs are preparing exceptional plans and training all staff to manage these patients with skill and safety, for the patient and themselves. Hospitals are acting to expand ICU care outside its existing footprint and double or even treble ICU capacity, most likely by taking over operating theatres. This expansion will involve engaging anaesthetists and others to provide ICU medical care and nurses from elsewhere in the hospital to work as ICU staff. To facilitate this, much or all routine surgery will need to stop. Many patients with Covid-19 will also be hospitalised outside ICU and care of these patients and those in ICU will have major consequences for caring for other patients who do not have Covid-19.

Whether these extreme precautions will be needed is unknown. If they are, whether even these measures will be sufficient is also unknown. We will find out over the next few weeks and months. In the meantime, preparations need to be accelerated and coordinated and we need to be honest and transparent about the potential impact of a Wuhan-type epidemic here in the UK, which no doubt will pose a major challenge to everyone working in the NHS.

• Tim Cook is a doctor in an NHS intensive care unit.

• This article was amended on 9 March 2020 to say that Britain ranked 24th out of 31 European countries in terms of ICU beds per head of population, not 23rd as an earlier version said.