Archie Battersbee's life support is due to be switched off at 11am today.
The 12-year-old boy's parents have been in a long-running legal battle as they fight to keep him on life support.
An appeal against the decision to end his treatment was refused by the Supreme Court on Tuesday.
Archie's mother, Hollie Dance, has confirmed that the family have submitted an application to the European Court of Human Rights to postpone the withdrawal of his life support treatment.
The family were given a deadline of 9am on August 3 to submit an application to the ECHR.
Archie has been on life support since April, after he was found unconscious at home.
His doctor's now believe that he is " brain-stem dead " and that it would be in his best interests to stop life support, but his parents disagree.
As Archie could have his treatment withdrawn today, here's what happens when life support is turned off and what brain death means.
What is brain death?
Brain death, which is also known as brain-stem death, is when someone who is on a life support machine no longer has any brain functions.
According to UK law, when someone is declared as brain dead, they are legally confirmed as dead.
Brain death means that the person will not regain consciousness or be able to breathe without support.
Someone who is brain dead doesn't have a chance of recovery because they will be unable to survive without artificial life support.
Being brain dead and in a vegetative state are different things.
A vegetative state, which can happen after serious brain damage, is possible to recover from.
However, brain death is permanent.
What happens when life support is switched off?
Life support doesn't always mean death.
Often, people are put on life support for a short time to aid their recovery and are taken off it when their body can survive by itself.
However, for those who are brain dead or in a permanent vegetative state, the decision may be made to turn life support off to allow the patient to die if there is no chance of recovery.
When a person who is brain dead is taken off life support, they will die within minutes because they will not be able to breathe on their own.
For someone in a permanent vegetative state who isn't brain dead, then passing away after life support is switched off can take longer, varying between a few hours to several days as the body's organs shut down.
