Air can enter an elephant’s body through three entrances, its mouth, trunk and forehead (through internal nares).
Elephant lungs have a unique lung physiology: they don't have a pleural space between the lung and the chest wall, In elephants, the pleural cavity is filled with connective tissue.
In 1681, a scientist in Dublin, Ireland, conducted an autopsy on an elephant that had died in a fire and wrote that the elephant's lungs were different from those of any other four-legged animal he'd ever seen. Their lungs are attached directly to the diaphragm and chest wall, allowing them to create much greater "vacuum pressure" for sucking water through their long trunks, while drinking.More than 2,300 years ago, Aristotle wrote about elephants crossing rivers and lakes completely submerged, with only the tips of their trunks above the water, like built-in snorkel tubes. Elephants alone can snorkel while deeply submerged underwater, since plates of the fibrous tissue can extend to accommodate the differential pressures during snorkeling and give the lungs room to breathe.The unusual lung structure enables elephants to withstand the extreme differences in pressure above and below water without rupturing blood vessels in the lining of the lungs.
This might be an indication that elephants evolved from aquatic mammals like manatees. (John B. West et.al. 2002)
During tranquilization, elephants must lay on the side in order to be able to breath. If they lie in sternum recumbancy to long time, they will die.
West, John B. 2002. "Why Doesn't the Elephant Have A Pleural Space," and "Snorkel Breathing in the Elephant Explains the Unique Anatomy of the Pleura." University of California, San Diego's Department of Medicine.