How does enteral ventilation via anus (EVA) work?

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Enteral Ventilation via Anus (EVA) Works by Delivering Oxygen Through the Rectum

Enteral ventilation via anus (EVA) is a method that allows mammals to absorb oxygen through their rectum. This process leverages the rich network of blood vessels present just beneath the rectal lining, facilitating the uptake of oxygen into the bloodstream. Researchers have demonstrated its effectiveness in mice, rats, and pigs through experimental trials involving both gaseous and liquid oxygen delivery.
Rectal Anatomy Facilitates Oxygen Absorption

The rectum's internal structure is key to the efficacy of EVA. It contains a dense mesh of fine blood vessels situated close to the surface of its lining. This anatomical feature is similar to how other animals, such as certain sea creatures, utilize their hindguts for oxygenation during emergencies. This proximity allows for efficient transfer of oxygen from the rectal cavity directly into the circulatory system.
Methods of Oxygen Delivery Demonstrated Effectiveness

Experiments have explored two primary approaches for delivering oxygen via the anus. The first method involves introducing oxygen in a gaseous form directly into the rectum. The second, and in some experimental contexts more effective, method uses an enema infused with oxygen-rich liquid. Researchers also found that preparing the rectal lining to increase blood flow, through mild inflammation caused by rubbing, enhanced oxygen delivery.
Liquid Oxygen Delivery Proved Safe and Effective

Beyond gaseous oxygen, the use of oxygenated perfluorodecalin, a safe liquid already in limited clinical use, was also successfully tested. This liquid-based approach, alongside gaseous delivery, demonstrably increased oxygenation levels in the tested animals. The procedure normalized their behaviour and significantly prolonged their survival rates, indicating a substantial improvement in their physiological state.
EVA Confirmed as Safe and Potentially Life-Saving

The research confirmed that EVA is a safe method, causing no discernible harm to the animals. The small quantity of liquid absorbed alongside the oxygen did not negatively impact gut bacteria or cause other adverse effects. This suggests a significant potential for EVA to support oxygen supply in patients experiencing respiratory distress, particularly during situations where conventional ventilators are scarce or insufficient, such as during a pandemic.

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How does enteral ventilation via anus (EVA) work?

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