Thrombosis and major bleeding events occur frequently in patients with COVID-19 who are being supported with veno-venous (VV) extracorporeal membrane oxygenation (ECMO), and both are linked with a higher risk of death, a study published in the British Journal of Haematology has found.

The team, led by Consultant Haematologist Dr Deepa Arachchillage, from the Department of Haematology at the Royal Brompton Hospital in London, assessed the incidence of major bleeding and thrombosis and the link with 180-day mortality in an observational study involving 152 adults with severe COVID-19 supported by VV ECMO.

Major bleeding was diagnosed in 31% of patients, at a median nine days from starting treatment with VV ECMO, with the most frequent type being intracranial (ICH; 34%), followed by pulmonary haemorrhage (26%), gastrointestinal haemorrhage (11%) and bleeding at other sites with a fall in haemoglobin of >20 g/l (6%).

Of the 47 patients who experienced a major bleeding event, 19% of events occurred within 24 hours of VV ECMO initiation, though the researchers noted that is uncertain whether these events took place just before ECMO or soon after, or whether they were caused by initiation of this intervention and associated changes to coagulation.

Thrombotic events were recorded in 63% of patients, with venous, arterial or ECMO circuit thrombosis rates of 45%, 19% and 10%, respectively. Of the 68 patients who developed venous thrombosis (VTE), isolated pulmonary embolism (PE) was the most common (66%) followed by DVT (19%) and combined PE and DVT (15%), according to the paper. Of the 81 venous or arterial thrombotic events, around half (52%) were diagnosed within a day of ECMO initiation.

The researchers noted that in multivariate analysis, only raised lactate dehydrogenase (LDH) at the initiation of ECMO was linked with a significantly increased risk of developing thrombosis (hazard ratio 1.92).

With regard to mortality, the study showed that patients who developed a major bleed after ECMO were 3.01-fold more likely to die, while mortality was higher in patients who developed ICH (HR 3.30) and even higher (HR 5·97) after adjusting for the patient age and duration of mechanical ventilation. PE was linked with a 2.12-fold increased risk of mortality.

The authors concluded that in COVID-19 patients receiving VV ECMO, “thrombosis and major bleeding events were frequent” and “likely multifactorial in origin”. They also noted that “major bleeds were independently associated with increased mortality,” which “emphasises the difficult balancing act between bleeding and thrombosis in COVID-19 patients supported with ECMO”.