Boris Johnson’s move to the intensive care unit (ICU) of St Thomas’ hospital signals that he has severe Covid-19. Oxygen was available through a mask on the ward he was admitted to on Sunday, but the move to intensive care on Monday strongly suggests that was not enough to help him with the breathing problems caused by the viral pneumonia that the virus triggers. Most people in intensive care, according to the World Health Organization, require ventilation. Around 15% of people with Covid-19 become seriously ill and need oxygen therapy in hospital. A further 5% are moved into intensive care, so that their breathing can be taken over by mechanical ventilation. Some will also need support for other organs. Anyone who is put on a ventilator will need to be sedated, although they are not unconscious. A tube must be inserted into the patient’s windpipe, so that air and oxygen from the machine can be blown into the lungs. That takes the strain off the lungs while they recover. Johnson, 55, is said to have been admitted to intensive care in case he should need ventilation, but 63% of those admitted to ICUs in England, Wales and Northern Ireland are ventilated within the first 24 hours. Guidelines from the National Institute for Health and Care Excellence (NICE) say that critical care treatment for Covid-19 should be started “with a clear plan of how the treatment will address the diagnosis and lead to agreed treatment goals (outcomes)”. Ventilation is vital in most severe Covid-19 cases, which is why there has been a huge effort to obtain more machines and even encourage engineering businesses to switch production lines to make them. In the severest cases, patients are put on an ECMO machine (extracorporeal membrane oxygenation), which can support both the heart and lungs where somebody is in a life-threatening condition. Johnson’s admission to intensive care comes shortly after the 10th day of the illness, which has been identified as a real danger point. During the first week, most people’s immune systems rally and manage to fight off the virus. Those who do not recover and continue to struggle for breath and have a fever often need help around the middle of the second week. In that second week, the immune system can sometimes go into overdrive. In its attempt to fight the virus, it creates what is called a cytokine storm, in which the immune system attacks the body’s own organs. The heart, the liver and kidneys are most likely to be affected and all of them can need to be supported by machines that can take over their function. The latest report into patients admitted into critical care so far from the intensive care national audit and research centre (IANARC), showed 2,621 admissions up to 3 April, most of whom are still there. The mean age was 60 and 73% of them were men. More than 35% of them were overweight, with a body mass index (BMI) between 25 and 30, and 37% were obese. Derek Hill, professor of medical imaging at University College London, said: “It seems clear that the prime minister went to hospital because he had difficulty breathing. It seems he was initially put on oxygen, and was conscious. “But as often happens with Covid-19, his condition has now deteriorated so he has been admitted to intensive care. “We understand the PM is on a type of breathing support called Continuous positive airway pressure (Cpap), which is commonly used in treatment of obstructive sleep apnoea. Experience in Italy and other European countries has shown that Cpap can be effective in Covid-19 patients, at least initially. Many Covid-19 patients progress to invasive ventilation. Invasive ventilation involves a tube being put down the patient’s airway.”