Euthanasia 

‘Sanctity of Life’ : idea that life is God-given (a gift). Life is sacred, worthy of respect and reverence, intrinsically worthwhile. People have a duty to respect and to preserve life. Catholic church: "euthanasia is an act/omission which of itself/by intention causes death in order that all suffering may in this way be eliminated". To do this is not allowed due to Natural Law, first primary precept of self preservation. However suffering can be great both physically and psychologically  that it can make a person wish to remove it at any cost. Suffering has a special place in God's plan of salvation. 
Doctrine of double effect:painkillers and drugs used to hasten death with a secondary effect of killing pain. 
‘Quality of Life’: Most would say we are a person when we think and act consciously. Some believe we are human from conception/birth: meaning embryos/comatose patients are still persons. Whereas some people say people in a permanent vegetative state may be a human but not really a person because they are unable to do so. Could be considered "incomplete" and already dead. When death is imminent a patient may refuse unnecessary treatment . Some say we cannot cease to be a person and yet be bodily alive. 
Right to life :duty of others not to kill a person (rules out Euthanasia). We don't see the duty to kill as absolute- wars can be justified, or killing in self defence, capital punishment, etc. It is easier to justify killing in voluntary euthanasia as the person chooses death. Life is a person's most valued and precious possession. Do we have a duty to kill them? Who has the duty? 
Do we have the right to choose when to die?
Applying ethical theories
Utilitarianism: Resources spent keeping them alive - more happiness could be produced if resources used for others. if continued existence brings  more pain and suffering than happiness, both to them and their family, then their life could be ended. "Death with dignity" as it seeks not just absence of pain but preservation dignity and exercise of personal autonomy. However, if people gain happiness and quality of life from death of one person, such action is justified- no protection of individuals against majority and no safeguarding individual's rights. 
Natural law: Doesn't look at people involved in situation- considers act itself. Protection of life as a primary precept goes against this. NL does allow patients to refuse treatment if it is above that necessary for existence. Weak santity of life: where death is inevitable, doctor treats with care and compassion but need not strive officiously to keep them alive.