Life support: a factfile

Nelson Mandela spent his 25th day Thursday in a Pretoria hospital, where his condition, brought on by a recurring lung infection, was said to be "critical but stable".

The 94-year-old anti-apartheid icon's family have said he is "assisted in breathing by a life support machine."

What does it do?

- A ventilator can assist an ailing patient with breathing -- absorbing oxygen and expelling carbon dioxide -- or take over the function altogether, depending on the state of the lungs.

How does it work?

- Non-invasive ventilation works with a mask that covers the nose or the nose and mouth and supplies oxygen. It is most often used with conscious patients.

- In more serious cases of breathing difficulty, a tube is inserted into the windpipe via the mouth or nose and connected to a ventilator. Intubation blocks the vocal cords and prevents the patient speaking.

- The breathing tube can also be inserted through a hole cut directly into the windpipe through the neck. This allows ventilation over a longer period, and permits the patient to speak.

Ventilators are often used to aid breathing after surgery or a stroke, for patients with lung muscle weakness or who are not strong enough to breathe on their own, and those whose lungs have been damaged by infection or trauma.

Mandela contracted tuberculosis while imprisoned for 27 years under the apartheid regime, which weakened his lungs. He has had several chest infections in older age.

Life support?

- The term is used for any mechanic assistance for a failing organ, whether it be a heart or lung bypass, kidney dialysis, or a feeding tube, required to keep a person alive.

- A person taken off life support, in line with their own final wishes or those of their family, will generally be given a sedative to ease their suffering.

Court papers filed Wednesday in a spat over the Mandela family burial site, revealed that the Nobel peace laureate's condition was "perilous".

Mandela's wife, Graca Machel, said Thursday that he was sometimes uncomfortable but seldom in pain.