The recent disclosures concerning Our Lady's Hospital for Sick Children and the country's maternity hospitals highlight the complexities of consent in medical practice. The parents of children whose organs were removed at autopsy have expressed their anger at the hospitals' failure to obtain consent for organ and tissue retention.

Consent is the legal expression of autonomy. A person has the right to offer or refuse consent to a treatment or procedure. Set against this there has been the historical scope given to medical practitioners to judge the amount of information needed to enable the patient to give valid consent.

As we move from an age of paternalistic healthcare to one of shared decision-making with the patient, the patient is now seen as a consumer.

This creates certain tensions which did not exist in the old-fashioned culture of "doctor knows best". No matter how benign the concept of medical paternalism was, it made presumptions which are incompatible with the giving of truly informed consent by the healthcare consumer.

Informed consent is the making of a rational and intelligent choice as to whether to submit to a proposed treatment or procedure. To make this decision, the patient needs to be given adequate details of the treatment and its risks.

Presumed consent, on the other hand, is much less specific. By presenting himself to a doctor's surgery or consulting room, the patient implies he wishes to be examined. This does not always include treatment, although, for example, if antibiotics are required for an infection, the consent to this course of action is usually presumed. When it comes to surgical treatment or more formal medical procedures, a doctor is expected to seek explicit and informed consent.

There are many exceptions to the normal rules of consent. One such exception occurred this week when the parents of a seriously injured child refused on religious grounds to give consent for blood transfusion as part of surgical treatment. The treating doctors immediately informed the gardai, who invoked their powers under Section 12 of the Child Care Act.

The child subsequently received the full range of medical treatment required for his condition, but without the specific consent of his parents. The local health board effectively became his legal guardians for the purpose of granting consent to life-saving treatment.

Consent for treating a child can legally be given by either a parent or guardian. This does not absolve a doctor of the duty to explain treatment to a minor in full. In Britain, minors may give valid consent if they fully understand the nature and consequences of the proposed medical intervention.

Can a child consent to the donation of an organ? This question has never been addressed by the Irish courts. In Western Australia, living children may not donate "regenerative material" - this precludes the removal of kidneys, liver and lungs, for example. French law used to permit the donation of organs by a child, but only to a brother or sister.

Can treatment ever be made compulsory? This issue represents a topical dilemma for the State's heath services. With a rise in the number of immigrants, fears have risen that tuberculosis and other infectious disease rates will increase. Can we force immigrants to undergo medical examination and treatment where necessary? The interests of the community suggests a role for compulsory screening; individual civil rights, on the other hand, demand that immigrant medicals be voluntary and subject to the rules of informed consent.

The pressing need for more kidney donations has led to calls for a change in the rules of consent in Britain. With a significant shortfall in kidney and other organs needed for transplants the British Medical Association has proposed an opt-out rule to replace the current system whereby donors "opt in" by carrying a donor card. In effect, this means going from a system of informed consent to one of presumed consent.

A spokeswoman for the Parents for Justice Group has expressed the view that most parents would give consent for organ removal provided it was explicitly asked for and that arrangements were made to return organs to families for appropriate disposal.

While the issue of informed medical consent has been usefully aired over the last few weeks, it is unfortunate that past practices have resulted in such distress to the parents and families concerned.

Muiris Houston is Medical Correspondent of The Irish Times