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Thursday, June 24, 2021

Explained: How anally delivered oxygen could one day save lives

Currently, patients with breathing difficulties are treated using tracheal intubation– a treatment whose critical importance was seen during the Covid-19 pandemic.

By: Explained Desk | New Delhi |
Updated: May 25, 2021 7:57:45 am
A health worker tries to adjust the oxygen mask of a COVID-19 patient at the BKC field hospital in Mumbai.(AP Photo)

While several animals breathe using lungs or gills, there are some species that use their intestines for this job. And as per new research, a medical procedure can be developed by which humans with severe respiratory illness too can be made to absorb oxygen through their intestines – a technique that can save lives when ventilators are in short supply.

This method relies on delivering oxygen to the intestines from the anus– the opening from which things generally exit the body. Yet, however unconventional some may find this technique – called Enteral Ventilation via Anus (EVA)– scientists are looking at it seriously, given the promising results seen in lab experiments.

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How can intestines absorb oxygen?

In vertebrates such as humans, meaning animals that have a spinal column, the intestines are connected with a large number of blood vessels that allow the absorption of digested food. Theoretically, scientists believe that the same blood vessels could also be able to absorb oxygen– something which a fish called the weather loach actually does.

Anally delivered oxygen can save lives when ventilators are in short supply.

Like most fish, loaches use their gills to take in oxygen from water. However, these fishes can also bring their head above the surface to take in a gulp of air. Loaches do not have lungs, and the swallowed air travels through their intestines, where the oxygen they need gets absorbed. Like loaches, catfish and orb-weaver spiders also breathe through their gut when the supply of oxygen in their surrounding dips, as per BBC Science Focus.

So far, though, no land vertebrates have been known to do this.

So, how can mammals be made to breathe through the intestines?

Research published on May 14 in the journal Med shows that like loach fishes, mammals too can be made to absorb oxygen from their intestines, with some external help.

In their experiments, the authors of the paper were able to successfully demonstrate their hypothesis on rats, mice and pigs, by supplying oxygen to the intestines from the rectum.

Anaesthetised and oxygen-deprived mice had oxygen pumped up the anus through to their intestines– a technique that helped them survive longer. However, for this method to work, the layers of mucous that line mammalian rectums had to be removed to be able to provide the oxygen direct access to the intestinal wall.

Aware of how unappealing this technique might be if it were ever to be used on human patients, the researchers worked out another one.

Instead of pumping in gas, the scientists then used perfluorocarbons– liquids that can absorb large amounts of oxygen– and which are used as a blood substitute and in the ventilation of premature babies. Using perfluorocarbons obviated the need for scraping off the rectal lining.

Anaesthetised mice with their linings intact were now administered perfluorocarbon enemas and placed in oxygen-deprived surroundings. Compared with animals that did not receive such a treatment, these mice were able to retain high levels of oxygen in their blood four times longer. Moreover, even after the time they spent in such conditions, the rodents’ behaviour appeared to be unaffected, said a report in The Economist.

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After successfully demonstrating their hypothesis on mice, the researchers moved on to rats and pigs, and obtained the same promising results. According to The New York Times, after being administered this enema, the mice started walking again, and the pale skin of pigs turned a healthy pink.

“They are completely recovering from the very, very severe hypoxia,” Dr Takanori Takebe, co-author of the Med paper, said to the NYT. “That was really astonishing to me.”

Can this treatment be safely extended to humans?

Buoyed by this success, Dr Takebe now expects to start trials on healthy human volunteers as early as next year. Currently, patients with breathing difficulties are treated using tracheal intubation– a treatment whose critical importance was seen during the Covid-19 pandemic.

Some experts believe that perfluorocarbon enemas could be less traumatic for patients with respiratory failure. However, it remains to be seen whether their weakened bodies would be able to absorb oxygen from the intestines.

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