The parents of a severely brain-injured boy are to appeal a High Court order to allow a hospital to withhold invasive treatment and instead administer palliative care should his condition substantially deteriorate.

The president of the High Court, Ms Justice Mary Irvine, said she would delay making final orders provided the parents initiate, by next Wednesday, an application aimed at securing an appeal direct to the Supreme Court.

Earlier this week, the court ruled the hospital is entitled to withhold invasive treatment for the boy who was catastrophically injured in a car accident earlier this year and is in a vegetative state.

In her judgment on Wednesday, Ms Justice Irvine said the parents' love for their child may have blinded them to the reality of his condition.

She ruled parental rights derived from the Constitution did not preclude State intervention in the case.

The 11-year-old boy, named only as "John", cannot be identified.

His parents had opposed the court orders and wanted him to receive all treatment to prolong his life regardless of the side effects.

However, the High Court ruled the boy could experience "unimaginable suffering" unless the hospital is allowed to manage his condition as doctors consider appropriate.

The judge praised the parents who had been a constant presence at their son's bedside since he was injured in a car accident.

The hospital had argued that invasive treatment would only damage him in the short to long term without improving his condition.

Judge Irvine said the orders sought by the hospital were in John's best interest and necessary to vindicate his rights.

She said the parents' love for their son has blinded them to the reality of his condition and may have contributed to their holding to the idea his pain is tolerable in the face of "a tsunami of evidence to the contrary".

She rejected arguments John's prognosis is unclear or uncertain and said there was as much certainty as there can be with any medical diagnosis that he will not recover in any significant way from his injuries.

The parents disagreed with the hospital's assessment concerning the pain being suffered by their son as a result of dystonia, which, unless fully controlled by medication, causes his muscles to contract uncontrollably.

They objected to John being medicated to treat pain caused by dystonia if there was a risk that would cause him respiratory distress and possibly die.