Physicians say coronavirus patients are suffering from life-threatening oxygen drops while in the emergency room that can lead to their death.

Dr Richard Levitan, is an emergency medicine practitioner at Bellevue Hospital in New York City, and has been teaching other medical professionals how to intubate and use ventilators for at least two decades.

But, in an op-ed for The New York Times, he wrote that he saw an interesting phenomenon in COVID-19 patients with pneumonia.

He was seeing patients that had lungs filled with fluid or pus, but they weren't struggling to breathe until the day they arrived at the hospital.

In fact, they had no idea they had the infection until they were in the emergency room and, by then, 'they were often already in critical condition.'

That's because many were suffering from hypoxia, can lead to low oxygen levels in the tissues, resulting in organ damage and - in some cases - death.

Dr Richard Levitan, an emergency medicine practitioner, said he saw COVID-19 patients with pneumonia come into the hospital with low oxygen levels. Pictured: A coronavirus patients on a ventilator in the emergency room at St Joseph's Hospital in Yonkers, New York, April 20

Levitan recommends patients be monitored with a simple device called a pulse oximeter (pictured) that measures oxygen levels before the dip too low

Hypoxia is a form of oxygen deprivation caused by hypoxemia, which occurs when there are low oxygen levels in the blood.

In the case of hypoxia, body tissues beginning run low on oxygen, which can result in infections and tissue damage.

A 2011 study from Massachusetts General Hospital found that approximately seven percent of patient experience a 'hypoxemic event' and 3.5 percent had a 'severely hypoxemic event' lasting two minutes or longer.

Hypoxia can occur without much warning and, without oxygen, your heart, liver, brain and other organs can be damaged within minutes.

'And here is what really surprised us: These patients did not report any sensation of breathing problems, even though their chest X-rays showed diffuse pneumonia and their oxygen was below normal. How could this be?' Levitan wrote in The Times.

He explained that the patients with COVID pneumonia causes call 'silent hypoxia' - silent because it's not often detected until an advanced stage.

Pneumonia is a lung infection that occurs when the air sacs are filled with pus or fluid, and patients with it have pain and discomfort.

But coronavirus patients with pneumonia don't feel the same shortness of breath despite their oxygen levels plummeting.

'And by the time they do, they have alarmingly low oxygen levels and moderate-to-severe pneumonia (as seen on chest X-rays),' Levitan wrote.

What are pulse oximeters? A pulse oximeter is a small clip device that can be attached to a part of the body, such as a finger or earlobe, to measure oxygen levels in the blood The device can be used to measure blood oxygen levels among those who have conditions such as asthma, congenital heart defects and pneumonia During a reading, beams of light pass through the blood in order to measure the changes of light absorption in oxygenated or deoxygenated blood The tests can be carried out in both inpatient and outpatient settings The devices cost upwards of £30/$30 and are available at pharmacies and online from sellers on Amazon and eBay. Advertisement

'Normal oxygen saturation for most persons at sea level is 94 percent to 100 percent; COVID pneumonia patients I saw had oxygen saturations as low as 50 percent.'

In fact, many were sick for at least a week with a fever, cough and lethargy before coming into the hospital.

So why is this occurring? Levitan writes that COVID pneumonia causes the air sacs in the lungs to collapse, which makes oxygen levels fall.

However, patients can still exhale carbon dioxide and, because it doesn't build-up like with normal pneumonia, patients don't experiences difficulty breathing.

Patients breathe deeper and faster due to their low oxygen levels, but they don't even realize it. And these changed breaths damage the lungs even more.

Due to the shortage of ventilators, and the likelihood of not coming off one once you're on, Levitan recommends that patients be monitored with a simple device called a pulse oximeter.

These are small devices that can be purchased at any pharmacy. They clip onto a finger to measure oxygen levels in the blood.

Levitan says this monitoring at home could alert patients for a need for treatment before their oxygen levels dip too dangerously low.

'Widespread pulse oximetry screening for Covid pneumonia - whether people check themselves on home devices or go to clinics or doctors’ offices - could provide an early warning system for the kinds of breathing problems associated with Covid pneumonia,' he wrote in The Times.