As the COVID-19 pandemic continues to place huge pressure on global health services, a shortage of ventilation devices has left many patients in danger of respiratory failure. However, new research reveals that mammals such as mice, rats, and pigs are in fact able to breathe through their intestines, suggesting that administering oxygen through the rectum may help to save the lives of humans suffering from respiratory issues.
It has long been known that certain aquatic species such as loaches and sea cucumbers are capable of taking in oxygen through their intestines in addition to their gills when faced with hypoxic conditions. Back in the 1950s and '60s, scientists conducted a number of experiments to determine if mammals shared this capability, yet results were inconclusive and the issue has remained a topic of debate ever since.
Appearing in the journal Med, a new study has finally settled the argument by providing evidence that mammals can indeed use their intestinal organs for respiration, and that doing so can significantly enhance survival and recovery rates following respiratory failure.
To begin with, the study authors removed the thin layer of mucus lining the gut of mice, in order to allow for enhanced diffusion of oxygen through epithelial cells. They then placed the rodents in a low-oxygen environment, which caused all of the animals to die within 11 minutes.
However, when the researchers delivered oxygen gas directly into the anus of mice, three-quarters of the animals were able to survive inside the chamber for 50 minutes. Repeating the experiment on mice that had not had their gut mucosal layer removed, the authors noted a significantly smaller improvement in survival rates, with rodents remaining alive for an average of 18 minutes.
While this finding indicates that mice are able to avoid respiratory failure by breathing through their buttholes, the need to remove gut mucosa makes this technique unsuitable for humans. The researchers decided to investigate an alternative method involving the administration of oxygenated liquid via the rectum.
To do so, they used a liquid form of oxygen known as conjugated perfluorocarbon, which is currently used in clinical settings for emergency ventilation by administration directly into the airways, and has proved effective at alleviating respiratory failure. When placed in a non-lethal environment containing just 10 percent oxygen, mice that received the liquid via their anus were able to walk considerably farther than those that did not, while the researchers also measured an increase in the amount of oxygen reaching the animals’ hearts.
The same technique applied to pigs also resulted in the animal’s skin becoming less cold and pale, in addition to increasing their ability to walk under low oxygen conditions.
"Artificial respiratory support plays a vital role in the clinical management of respiratory failure due to severe illnesses such as pneumonia or acute respiratory distress syndrome," explained study author Takanori Takebe in a statement. "The level of arterial oxygenation provided by our ventilation system, if scaled for human application, is likely sufficient to treat patients with severe respiratory failure, potentially providing life-saving oxygenation."