ECMO and the Treatment of Severe Covid-19

A glimpse into the procedure saving dozens of patients with severe Covid-19

The word bypass carries many meanings in medicine. When a person suffers from heart disease, often doctors harvest a vein from the leg and sutured it around clogged coronary arteries creating a route around the blockage. Similarly, when people with advanced diabetes arrive at dialysis centers, they submit themselves to a process by which blood is diverted away from damaged kidneys into a dialysis machine where it can be separated, and its waste products removed before being returned to the patient’s ciruclation. Even in utero the fetal cardiovascular system has valves in place to strategically bypass organs that would otherwise act as a oxygen drain, robbing the developing fetus of crucial oxygen from the mother. Ironically, this system of fetal circulation bypasses the very organ in the womb that will one day be the sole source of oxygen in life: the lungs.

The major cause of mortality in Covid-19 results from the symptoms that arise when the lungs are severely damaged. Deep inside the lungs are millions of delicate air sacs where air is exchanged between the outside environment and the blood stream. The thin structure of lung air sacs — called alveoli — coupled with the massive surface area of the lungs is what makes gas exchange so efficient. When air comes in, oxygen floods into the blood, while CO2 escapes out.

The thin barrier that divides air from blood, often only one or two cells thick along with a small amount of connective tissue, is known as the interstitium. This thin barrier is one of the primary targets of SARS-CoV-2. As the virus gains access to the interstitium, the immune system is activated. Swelling is one of the most common responses to immune activity. Swelling is benign and harmless in many cases of immune or allergic response, but when the uber-thin interstitium of the lungs swells, it may actually expand to two or three times its normal width, dramatically decreasing gas exchange.

As the immune response further escalates, fluid from the interstium leaks out into the alveoli and fills the space where air normal goes. This fluid, laden with viruses and other opportunistic pathogens is quickly followed by immune cells and soon the once delicate air-filled alveoli become thick, congested fluid filled masses. This is pneumonia. Many Covid-19 patients rapidly progress to a state where gas exchange is so compromised that they go into acute respiratory distress syndrome (ARDS). This is where doctors can employ extracorporeal membrane oxygenation — known simply as ECMO.

ECMO Explained

ECMO follows the principle of bypass by relieving the lungs of the duty of gas exchange. Following similar principles as kidney dialysis, blood is pulled from the veinous circulation — where oxygen concentrations are lowest — and sent through a pump system that shuttles blood into an oxygenator that oxygenates the blood, while removing CO2 waste. Once blood is fully oxygenated, it is sent through a heat exchanger that brings it back to body temperature and returned to the body’s circulation. This newly oxygenated blood is then delivered to tissues by the heart.

ECMO was developed in the 1950’s as a life support technique. In modern times it is common to see hospitals with devoted areas for ECMO care of critically ill patients suffering from acute heart or lung failure. ECMO also plays a critical role in emergency rooms. Patients suffering from cardiac arrest often undergo cardiopulmonary resuscitation (CPR) to artificially restore both blood oxygenation — through breaths — and circulation — through chest compressions.

CPR in itself is a crude practice. It relies on techniques that are susceptible to human error. Patient head position, timing and depth of breath delivery, timing and location of chest compressions are all variables that lead to sucessful or non-successful CPR. Even chest compressions deep and forceful enough to compress the heart are enough to crack the ribs of patients. Despite how it is portrayed on TV medical dramas, CPR is a violent procedure with poor rates of success. ECMO can offer a better — albeit a more invasive — option in life support.

Recognizing the value of ECMO in cases of emergency, the University of Minnesota went one step farther and took ECMO out of the hospitals and onto the streets by creating their own mobile EMCO unit — the first of its kind in the nation — to respond to medical emergencies that involve cardiac or pulmonary arrest.

ECMO Versus Mechanical Ventilators

Mechanical ventilators have received a lot of attention since the onset of the Covid-19 pandemic. These machines, which artificially breath for critically ill patients, are often the last resort for those Covid-19 patients in severe respiratory distress. Placing a patient on a ventilator is considered to a serious and often ominous sign that they are teetering on the edge of survival. Ventilators and ECMO serve the same end function — to maintain the delivery of oxygen-rich blood to tissues — but do so in different ways.

When we breath, we the lungs are working to balance two key aspects of respiration: ventilation — the delivery of air to the lung tissue — and perfusion — the delivery of blood to lung tissue. When air and blood are brought into close proximity, gas exchange can occur. Gas exchange itself is a passive process where gases move from areas of high concentration to areas of low concentration. This process — called diffusion — requires no added energy or mechanical force. Ventilation on the other hand is an active process, requiring the work of muscles in the body to move the lungs like a bellows. The rhythmic movement of muscles like the diaphragm and those that surround the rib cage draw air in and out allowing for constant gas delivery to and from the lungs.

In severe cases of Covid-19, the lungs not only lose the ability to exchange gases as describe above, but can become so damaged by the virus that they lose the ability to ventilate. This loss of lung function — the active movement of lungs by the chest wall — requires a ventilator that forces are into the lungs. If enough viable lung tissue exists, ventilation may be sufficient to facilitate the gas exchange needed to sustain life. This procedure requires that patients be anesthetized and intubated — the placement of a tube directly into the lower respiratory tract — for the ventilator to function. ECMO, on the other hand can be performed at the bed side with simple sedation, assuming the patient’s lungs are ventilating properly on their own. Patients who have lost the ability to ventilate would need to be placed on a ventilator before they were able to undergo ECMO.

The Downside of ECMO

For all of its value, ECMO comes with its own risks. If nothing else, the procedure is invasive, requiring the placement of tubes into large vessels in the neck or leg. This carries risks of infection at the incision site that may enter the blood stream. Infections at the site of IV or central lines in the hospital is a common occurance. There is also an increased risk of blood clotting as a result of the procedure, which often requires patients be put on a blood thinner while undergoing ECMO. As we have seen from various reports, Covid-19 patients are already at an increased risk of blood clots, making this precaution ever more important when deciding to use ECMO for severe Covid-19 cases.

Even with ECMO in place, the body is still in the midst of fighting the Covid-19 infection. Because ECMO in no way protects the lungs from the damage of the viral infection, it is purely a life-sustaining procedure and not a treatment for the underlying infection.

Advancing knowledge of human physiology allows health care providers to bypass the normal functioning of the body in times of crisis. The strategic overriding of body systems can allow for controlled implementation of life-saving intervention. While many race to find treatments, or develop vaccines against Covid-19, the need for efficient life support techniques is needed in hospital ICUs to avoid rising mortality from the disease. ECMO offers a simple solution to preserving one of the cornerstones of human life — respiration.

Covid-19: Is the worst finally over?

For as long as I can remember, I have identified as an optimist. Like a seedling reaching toward the golden sun, I’m innately tuned to seek out the bright side.

Of course, in recent years this confidence has grown tougher to maintain. The industry I’ve long covered, technology, has lost its rebel edge, and grown monopolistic and power hungry. The economy at large echoed these trends, leaving all but the wealthiest out in the cold. All the while the entire planet veered toward uninhabitability.

And yet, for much of the last year, I remained an optimist. In the US a re-energised Democratic Party looked poised to push for grand solutions to big problems, from health care to education to climate change.

Perhaps we should spend more time considering the real possibility that every problem we face will get much worse than we ever imagined. The coronavirus is like a heat-seeking missile designed to frustrate progress in almost every corner of society, from politics to the economy to the environment

There was finally some talk about reining in monopolies and creating a fairer economy. Things weren’t looking good, exactly, but if you squinted hard, you could just make out a sunnier future.

Now all that seems lost. The coronavirus and our disastrous national response to it has smashed optimists like me in the head. If there is a silver lining, we’ll have to work hard to find it.

Perhaps we should spend more time considering the real possibility that every problem we face will get much worse than we ever imagined.

The coronavirus is like a heat-seeking missile designed to frustrate progress in almost every corner of society, from politics to the economy to the environment.

The only way to avoid the worst fate might be to dwell on it. To forestall doom, it’s time to go full doomier.

Choose your own facts

In a book published more than a decade ago, I argued that the internet might lead to a choose-your-own-facts world in which different segments of society believe in different versions of reality. The Trump era, and now the coronavirus, has confirmed this grim prediction.

That’s because the pandemic actually has created different political realities. The coronavirus has hit dense, racially diverse Democratic urban strongholds like New York much harder than sparsely populated rural areas, which lean strongly to the GOP.

That divergent impact — with help from the president and his acolytes — is feeding a dangerous partisan split about the nature of the virus itself.

Consider the emerging culture war about wearing masks or about whether to take certain unproven therapies. Look at the protests over whether it’s safe to reopen.

Now play these divisions forward. As The New York Times’ Kevin Roose wrote, when a vaccine does emerge, what if many Americans, fed on anti-vax rumours, simply refuse to take it?

Create further inequality

The virus’s economic effects will only create further inequality and division. Google, Facebook, Amazon and other behemoths will not only survive, they look poised to emerge stronger than ever. Most of their competition — not just small businesses but many of America’s physical retailers and their millions of employees — could be decimated.

Worst of all, it’s possible that the pain of this crisis might not fully register in broad economic indicators, especially if, as happened after the 2008 recession, we see a long, slow recovery that benefits mainly the wealthy. There are already signs that this is happening: Thousands died, millions lost their jobs, but stock indexes are rebounding.

The economic impacts feed into the political ones: The virus-induced recession could further affect the news industry.

Even worse, the virus is making a hash of emerging solutions to entrenched problems. As Conor Dougherty chronicled in “Golden Gates,” his recent book on America’s housing crisis, activists have lately been finding success in pushing to build more housing in restrictive regions like the San Francisco Bay Area.

The virus may put such reforms on ice. And consider the grim future of public transportation after the pandemic: Will people just get back in their cars, driving everywhere they go?

I called a few economists, activists and historians to discuss my growing alarm about the future. Many were less pessimistic than I am; some suggested that the virus could prompt much-needed action.

The most instructive example is the Great Depression. In the 1930s, after years of inaction, reformers who came into office with Franklin D. Roosevelt were able to push through laws that improved American life for good.

Matt Stoller, an anti-monopoly scholar at the American Economic Liberties Project, a think tank, agreed that this crisis could be the jolt we need to fix US institutions.

But he also noted that the United States has failed to make the best of our most recent national calamities. The 9/11 attacks pushed us into needless quagmires in the Middle East. The 2008 recession deepened inequality.

Let us not squander another crisis. We need to take a long, hard look at all the ways the pandemic can push this little planet of ours to further ruin — and then work like crazy, together, to stave off the coming hell.

Farhad Manjoo is a noted American columnist and author

Source : New York Times

People with COVID-19 may be infectious days before symptoms: study

Study comes as nations have broadened restrictions aimed at curbing coronavirus

Paris: People infected with the new coronavirus may start spreading the virus several days before they have any noticeable symptoms, according to a new modelling study published Wednesday.

The study comes as nations have broadened restrictions aimed at curbing the epidemic, amid concerns over patients who may be infectious despite not showing signs of ill health.

The findings challenge key assumptions behind measures put in place to stop the spread of the pandemic, such as tracing contacts of an infected person only as far back as the time at which they began to show symptoms.

Experts have long conjectured that some people who do not even know they are infected may transmit the virus.

But the new study suggests that even those who get visibly sick may be highly infectious before the onset of symptoms.

“More inclusive criteria for contact tracing to capture potential transmission events two to three days before symptom onset should be urgently considered for effective control of the outbreak,” the authors said in the paper published in Nature Medicine.

Infectious before symptoms show 

Researchers compared clinical data on virus shedding from patients at a hospital in China with separate data on “transmission pairs” – where one person is believed to have infected the other – to draw inferences about periods of infectiousness.

The research team co-led by Eric Lau of the University of Hong Kong took throat swabs from 94 patients admitted to Guangzhou Eighth People’s Hospital and measured infectiousness from the first day of symptoms for 32 days.

They found that the patients, none of whom were classed as severe or critical, had the highest viral load soon after the onset of symptoms, which then gradually decreased.

The study used publicly-available data on 77 transmission pairs, within China and internationally, to assess how much time elapsed between the onset of symptoms in each patient.

It assumed an incubation period – the time between exposure to infection and appearance of symptoms – of a little over five days.

The authors inferred that infectiousness started 2.3 days before symptoms appeared and was at its peak at 0.7 days before the first signs of illness – although they cautioned that pinpointing the exact timing of the onset of symptoms relied on patient memory.

They estimated that 44 percent of secondary cases in the transmission chains were infected during the pre-symptomatic stage.

Infectiousness was predicted to decrease quickly within seven days.

‘Important implications’ 

Responding to the study, Babak Javid of Tsinghua University School of Medicine in Beijing said the findings would have “important implications” for measures to control the pandemic, such as whether masks should be worn by those with no symptoms.

“This is important because current public health control measures advised, for example, by the WHO and UK government assume that maximum contagion is after symptom onset. Hence one reason masks are not advocated for wearing by asymptomatic members of the public,” he said.

Javid added that several studies had now suggested that a large number of patients shed the virus before they show signs of illness and said the findings are “likely to be real and robust”.

At the beginning of this month China said it had more than 1,300 asymptomatic coronavirus cases, the first time it has released such data following public concern over people who have tested positive but are not showing symptoms.

As the pandemic has spread, many nations that initially advised only individuals with symptoms to self-isolate and wear masks have expanded their responses to measures that apply across the board.

The US Centers for Disease Control and Prevention (CDC) has said up to a quarter of people who are infected may be asymptomatic.