Concern over ‘silent’ oxygen deprivation prompts new approach to virus

Health officials in Brazil order mass monitoring of patients’ blood

Health officials in Brazil are ordering the mass monitoring of blood oxygen among coronavirus patients because of mounting concern about people having dangerously low levels even if their symptoms are mild.

Doctors worldwide have voiced alarm over “silent hypoxia” — a shortage of blood oxygen that does not always cause a shortness of breath and can result in people not seeking medical help until their condition is critical.

With Brazil gripped by one of the world’s worst virus outbreaks and a death toll that experts say is possibly heading for 100,000, community health services and NGOs in São Paulo and Rio have begun monitoring oxygen levels among patients in the cities’ crowded favelas.

Rio de Janeiro’s state health service said it would change its orders to doctors, telling them to admit to hospital patients with mild symptoms in the early stage of the disease rather than sending them to isolate at home as before. It follows a similar move by city health officials in São Paulo.

The changes contrast with standard procedure in other countries such as the UK, US and France, where people with mild symptoms are told to self-isolate at home and seek medical attention only if they begin to experience more severe problems, such as difficulty breathing and bluish lips.

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The World Health Organisation has advised people experiencing a cough and fever to remain at home, but to seek help if they develop difficulty breathing.

Signs of the potential danger of that approach have been picked up by doctors and researchers in several countries since at least the middle of April.

Silent hypoxia is “quite newly observed but also quite significantly concerning”, said Jeremy Rossman, lecturer in virology at the University of Kent. Although telling people to self-isolate at home helps curtail the spread of the virus, some cases of serious illness are being “missed” until people are “critically unwell,” he said.

A Covid-19 guide published by the UK’s health service in April warned that “‘silent hypoxia’ is common”, though the NHS could not provide any data to support the claim. A guide published by a group that represents London doctors said pulse oximeters — simple, clip-on-the-finger devices that measure oxygen — could be “a very useful tool in helping to monitor and assess patients”.

In Brazil, Esper Kallas, an infectologist and professor at the University Hospital of São Paulo, said that by the middle of April: “We had begun to see a lot of people arriving at the hospital when they were already very sick. Most of them didn’t know they had hypoxia and were not feeling any shortage of breath.”

He discussed this with a colleague at the Hospital M Boi Mirim in one of the poorest neighbourhoods of São Paulo, where many Covid-19 patients were dying within two days of being admitted to hospital. They decided to tell their patients, wherever possible, to monitor their blood oxygen levels at home with a pulse oximeter — typically available for about $30.

Pércio de Souza of the Instituto Estáter, a private foundation, has been agitating for early intervention in cases of Covid-19 through hospital admission or home oxygen monitoring. But with the federal government in disarray and president Jair Bolsonaro campaigning against lockdowns by state governors, he has concentrated on local government and civil society.

One project is being trialled by SAS Brasil, a healthcare NGO, which uses motorbike riders to deliver oximeters to favelas in São Paulo and Rio de Janeiro, sometimes leaving them with patients along with a mobile phone so they can take multiple measurements a day and share them with a doctor.

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Adriana Mallet, a founder of SAS Brasil, said they found that blood oxygen saturation fell in half of the 1,400 cases they saw in Jardim Colombo, a São Paulo favela.

She said some patients in favelas “find it hard to understand what public health campaigns want them to do, and many of them are scared to seek help and end up arriving [at health services] when it’s too late”. She added: “Giving them access to oximeters is essential to prevent avoidable deaths.”

Elsewhere, in the absence of more clear advice from policymakers, some hospitals and medical groups in other countries are advising Covid-19 patients to monitor their blood oxygen levels. 

Hospitals in several US states have started giving Covid-19 patients pulse oximeters in an effort to free up hospital beds for the most unwell.

This month, both the US Centers for Disease Control and Prevention and the UK government recommended that care homes use oximeters to monitor symptomatic residents.

Editor’s note

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