Is it true that Covid-19 kills by thrombosis and not by pneumonia?

The publication has actually been circulating for several weeks in many languages ​​(notably in Italian, where it is this time attributed to an anonymous “cardiologist from Pavia”…). This mixes some real information with many dubious, even false, allegations and extrapolations.

Thrombosis is just one of the possible complications

Over the past four months, numerous observations have been made showing that one of the possible complications of severe forms of the disease is DIC (disseminated intravascular coagulation). In other words: the formation of small blood clots that impede blood circulation (thrombosis) and disturb the coagulation, causing hemorrhages. These clots are said to form in particular in the pulmonary vessels. As of February, a study conducted in Wuhan by researcher Tang Ning reported that out of 21 deceased patients, 15 probably presented a DIC.

However, DIC is not the only form of thrombosis seen in severe cases of the disease. Above all: thrombosis is not observed in all intensive care patients.

In a French study to appear in the journal Intensive Care Medicine, 64 thrombotic complications have been identified in 150 patients with severe forms of Sars-CoV-2 infection. This event was significantly more frequent in Covid + patients than in a group of patients with acute respiratory distress syndrome unrelated to the coronavirus. The authors note that none of the 150 Covid + patients developed CIVD. A similar finding was made in a Dutch study of 184 patients (31% thrombosis, no DIC).

The rate of pulmonary embolism – usually caused by thrombosis – also appears to be particularly high in hospitalized patients. Pulmonary angioscanners (scanners performed with injection of contrast agent) performed at the Besançon University Hospital by the P team^r Eric Delabrousse out of 100 consecutive patients with a severe form of the disease thus revealed 23 cases of pulmonary embolism. The embolism involved 17 of 39 patients in intensive care.

A known and taken into account

One possible explanation for these frequent complications (arterial damage, development of clots) could be the affinity of the virus for the cells constituting the walls of the vessels, and the emission of coagulation factors by these same cells.

The frequent over-risk of microthrombosis is sufficiently known for the ISTH (International Society of Thrombosis and Hemostasis) to present recommendations on March 25 for the use of an anticoagulant (low molecular weight heparins) in certain patients with severe forms of Covid-19. In a leaflet published on April 11, the scope of use of this drug was specified by the Italian Medicines Agency (AIFA), which also gave the green light to its clinical evaluation for this indication. The benefits of heparin in some Covid + patients with infection-related bleeding disorders were reported by the Tang Ning team in late March. The value of other forms of heparin is also discussed.

In any case, the use of high-dose anticoagulants (beyond the doses commonly used to limit the risk of venous thrombosis in intensive care patients) seems to be of no benefit in many Covid + patients in intensive care including the clinical picture does not suggest a thrombotic event.

Swiss autopsies put those carried out in Italy into perspective

Let’s go back to the message relayed on social networks. Autopsies of Covid + patients have indeed been performed in Milan and Bergamo (more than 80 in the latter city since mid-March). A sighting report was pre-published on April 22 on the site medRxiv (which gives access to articles before independent critical review and publication).

According to this study, which involves 33 men and 5 women, a DIC was observed in the small arterial vessels in all lung tissue analyzed. The authors also describe characteristic lung lesions (diffuse alveolar damage, or DAD), already described “For the other two coronaviruses that infect humans, Sars-CoV and Mers-CoV”.

The fact that a DIC was observed in these 37 Italian patients is notable. But it does not allow, as viral publication does, an abusive generalization according to which thrombosis is systematically involved in all deaths. Published in early May, Swiss autopsy data on 21 individuals paint a more mixed picture. Thus, microthrombosis in the vessels of the alveoli was only observed in five individuals. Pulmonary embolism was observed in four, and diffuse exudative alveolar damage in 16.

Pneumonia, the most common complication of Covid-19

“Pneumonia remains the most common reason for admission to intensive care, explains Thomas Gille, pulmonologist at the AP-HP. It is the main possible complication of Sars-CoV-2 infection. We are both sick because of the effect of the virus on lung cells, but probably even more because of the disproportionate immune response in response. Difficult to differentiate these two components on the scanner: it is this set that is known as pneumonia. “

“In severe forms, the inflammatory reaction can take over, turning pneumonia into an acute respiratory distress syndrome. Moderate pneumonia can occur alongside a pulmonary embolism. Those are two different things.”

Why respirators are essential

Contrary to what the Facebook post implies, the authors of the Italian study on autopsies do not at any time question the interest of respirators.

Questioned by CheckNews, the P^r Alexandar Tzankov, head of Swiss works, strongly criticizes the assertion of the viral message according to which “respirators and intensive care units were never needed. ” “Many critically ill patients require respiratory assistance. Maybe it should be done with lower oxygen saturation thresholds and increased plasma transfusions … But there is no data to suggest giving up breathing assistance ! ” Equally untrue is the allegation that increasing places in intensive care “Was not necessary”.

When the cells lining the alveoli are infected with the virus, their destruction will have a direct consequence: the lungs can no longer properly oxygenate the blood. It is necessary to use a respirator to increase the oxygen supply. The same problem occurs when the infection leads to thrombosis in the pulmonary vessels. Mechanical ventilation may sometimes be necessary. It allows the survival of the most severely affected patients, maintaining maximum oxygenation of healthy alveoli as long as clots obstruct blood circulation.

In summary

The formation of clots in the vessels supplying the lungs is only one of the possible complications of Sars-CoV-2 infection, not the systematic cause of Covid-19 symptoms. The use of high doses of anticoagulants has no effect, and even potentially harmful, in many cases.

Note that in France, a new clinical trial for the prevention of the risk of thrombosis will be carried out on 600 Covid + patients, under the coordination of P^r Stéphane Zuily (Nancy CHRU). The first patient was included on March 13.

Florian Gouthière

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