Hi Vince,
This is how I see these 2 situations.
1) If a person chooses not to place a dying parent of life support.
If the persons intention is to kill the parent by not placing him on life support then it is an ananthariya kamma. Placing on life support is only one medical option, and just because one is placed on life support does not mean that the patient has a 100% chance of living. There are instances where different doctors propose contrasting treatments to the same patient. The patient’s family will have to choose one over the other. I think life support should be viewed in a similar manner.
2) If the person chooses to switch off the life support.
If such a decision is made and the patient dies because of an action following that decision, then an ananthariya kamma may be created. When one decides to switch off a patient’s life support, the intention more often is to cease the patient’s life. However there are instances where the patient lives on even after the life support is switched off, and in such a case no ananthariya kamma will take place although a grave papa / akusala kamma will be created, due to the decision to switch off the life support.
Going back to point 1): If we know that we may face a situation like situation 2) if we choose to put someone on life support, then I believe the safest would be not to put the patient on life support.