Filtering blood may combat Covid-19
AFILTER packed with beads that work like a sponge could be used to treat Covid-19. The device removes potentially toxic compounds called cytokines by purifying patients’ blood.
The size of a drinking glass, it is designed to distinguish between toxins and other blood constituents. Holes in the beads catch and remove the cytokines but won’t trap smaller, beneficial particles, such as antibodies.
Usually cytokines — proteins produced by immune cells — help co-ordinate the body’s attack on infection. In severe cases of Covid, however, this response can go into overdrive, creating a ‘cytokine storm’ with potentially damaging levels of inflammation. This can lead to acute respiratory distress syndrome (ARDS), where lungs struggle to fill with air.
The blood-cleaning device was developed in the US to treat sepsis, which can also spark a cytokine storm and lead to organ failure. The CytoSorb device is already approved for sepsis.
In April, the US Food and Drug Administration stated it could help treat Covid-19 cytokine storms. In May, the National Institute for Health and Care Excellence, produced guidance on its use against the virus.
The guidance was based on evidence from three small trials in China, Germany and Italy.
The largest involved 11 patients with ARDS whose blood showed a significant reduction in inflammatory markers (chemical signs of inflammation) after being passed through the CytoSorb filter for up to 48 hours.
Trials are being held to judge its effectiveness against Covid and over 1,200 patients have been treated in 30 countries so far.
The filter can be attached to hospital dialysis machines typically used to filter excess fluid and waste from the bloodstreams of patients with kidney failure. A tube is attached to a blood vessel in the neck or leg and blood is pumped from the body through the filter where the beads absorb the cytokines.
The filtered blood is then circulated into the patient, before being passed back into the cartridge for further purification. It is claimed in one 24-hour session the body’s entire blood volume is filtered more than 70 times.
Patients with severe respiratory symptoms of Covid-19 are usually ventilated (where machines help the lungs to inhale and exhale air) to help increase oxygen levels.
But with no vaccine yet available and studies estimating the death rate of patients in intensive care units at about 41.6 per cent (reported in the journal Anaesthesia in July), new and better treatments are needed urgently.
By lowering cytokine levels, the CytoSorb could help quell cytokine storms in coronavirus patients and improve their chances of recovery.
Simon Clarke, an associate professor of microbiology at the University of Reading says: ‘Technologies like this blood filter could prove to be very useful, provided they can be used on the patient quickly enough.
‘For patients with a significant cytokine response, time is of the essence. In the same way drugs might only dampen the response, filtering is not a guaranteed success, but the sooner you get it to the patient, the better.’