While doctors have long been making decisions to withdraw ''life support'' measures for people in circumstances where the care is futile or the patient does not want to live with extreme disability, they say increasing requests for people's pacemakers to be turned off raise difficult ethical questions and may even expose them to criminal charges of murder, manslaughter or assisted suicide.

A leading intensive care specialist from Newcastle, Peter Saul, said one technician at his hospital refused to turn off a dying woman's pacemaker at her daughter's request because he feared being accused of killing the woman in potentially unethical or illegal circumstances.

When that happened, Dr Saul was called to assess the request which involved an elderly woman who had suffered a series of infections over months. He said the woman, who had pneumonia and was suffering breathlessness and bed sores, had lost a lot of weight and was very drowsy.

While it was estimated she would die ''within days, not months'', she was unable to express her wishes about whether she would like her pacemaker switched off to hasten her death. Her daughter believed she would not want to go on living and insisted the pacemaker be turned off.

Dr Saul said this put him and his colleagues in a difficult position because usually medical treatment is withdrawn when it is obviously burdensome, such as in the case of a ventilator placed down someone's throat. This means the primary intention of the decision is to relieve someone's distress, not cause their death, even though the withdrawal of treatment will end their life.

''The problem we had with the pacemaker case is that we knew when we pressed the button which said 'turn off the pacemaker', that the patient would become unconscious in five seconds and be dead within a minute. So saying that we weren't causing the patient's death was challenging because it felt very much like we were,'' said Dr Saul, of John Hunter Hospital and Newcastle Private.

''The standard argument is that the patient already had the illness that the pacemaker was put in to treat and that all we're doing is letting them die of the illness they had in the first instance. So, it's morally the same as if we never put the pacemaker in in the first place.

''But that doesn't stand up to much scrutiny when you talk like that because the pacemaker had been with her for some years. It wasn't burdensome, she was quite unaware of its functioning, so the excuse for turning it off was unclear, other than a wish that she would die painlessly. But why is that any different from the things that are illegal and that we're not allowed to do?''

Dr Saul said the case highlighted the difficult decisions doctors are increasingly making in end-of-life care, which involves a wide spectrum of actions that could be viewed by some as euthanasia or physician-assisted suicide, both of which remain illegal in Australia.

''What's to stop someone turning around and saying we did something illegal? And that isn't just about the risk of getting sued - you can get put into prison for murder or manslaughter. So, you can understand why doctors are anxious about this whole idea that there are places on the spectrum of euthanasia that are safe places to go and places that are absolute no-go areas, and yet we can't actually clearly identify where that point is.''

Dr Saul said another patient had since had their pacemaker switched off when it was clear he would die within a day. But he said with tens of thousands of Australians wearing the devices (one is implanted every 15 minutes in Australia), as well as implantable defibrillators and artificial hearts, he expects more people will either demand they be switched off or have someone demand it for them.

With this in mind, he said people should write their wishes down in an advance directive to make it easier for themselves, their families and doctors.

''Clearly a better defence for us is saying well this is what the patient wanted...you're on very safe ground with that. It's when a surrogate is making that claim on your behalf that we feel vulnerable,'' he said.

Moral philosopher and professor of bioethics at Princeton University Peter Singer said he did not see anything wrong with switching off someone's pacemaker at their request or the request of an appropriate surrogate decision maker, but said people with the devices should spell out the circumstances in which they would like them turned off to make it clearer for everyone involved.

While not everyone will die immediately when their pacemaker is turned off, Professor Singer said wearing one could offer people more choice about when and how they die. For example, if someone is diagnosed with an illness they do not want to live through or an illness has become too painful for them, they could ask a doctor to switch off their device.

''It puts them in the fortunate situation of anyone in the Netherlands who has reached a point where they say the quality of my life has fallen below an acceptable level, there's no chance it will recover to an acceptable level and the doctors agree that it won't, so I've had enough. So whereas you can't say give me a lethal injection [in Australia], you can say I've got a pacemaker so please turn it off,'' he said.

Pioneer of the Respecting Patient Choices program at the Austin Hospital Bill Silvester said while he had not encountered people wanting their pacemakers switched off, doctors were frequently asked by families of someone with dementia not to replace their pacemaker batteries.

''Most of the cardiologists comply and the families are told that in time the pacemaker will fail and the families are fine with that...It would appear that the families equate death at the time the machine fails [because of the battery running flat] to 'nature taking its course','' he said.

But Associate Professor Silvester, an intensive care specialist, said people should write an advance directive that expresses the circumstances in which they do not want to live because they have a right to refuse medical treatment.

''Based on the principle of autonomy, it's still up to the patient, so if you said I just found out I have dementia, I don't want to even progress at all in the trajectory of this condition where I'm going to lose the dignity of not recognising family at all, or even to the point where my family is questioning my decisions because I got lost on the way home...so I want to stop much earlier in the severity of the dementia, I reckon it's up to them,'' he said.

But would a doctor agree to turn off a pacemaker in such a person? Associate Professor Silvester said it could only be dealt with on a case by case basis.

''I have most success in getting through to doctors who struggle with that, by saying well what if that was you? Would you like to have a say in what goes on? And invariably they say, they would...When they do it for the first time, they might find it difficult, but as the precedent gets set and it's seen to be within normal medical practice, they will probably feel less uncomfortable about doing that,'' he said.