Substitute Decision Maker South Australia: How to Choose and Appoint Your SDM

What a Substitute Decision-Maker Does in South Australia

A Substitute Decision-Maker (SDM) in South Australia is the person you legally appoint to make healthcare, personal, and lifestyle decisions on your behalf if you lose the capacity to make those decisions yourself. The appointment happens through your Advance Care Directive (ACD) under the Advance Care Directives Act 2013.

This isn't a vague "I'd like my daughter to handle things" arrangement. It's a statutory appointment with legal force. When your ACD activates — meaning a medical professional has assessed that you've lost decision-making capacity — your SDM steps into your shoes for every decision covered by the directive.

Their authority includes consenting to or refusing medical treatment, choosing where you live, deciding about aged care placement, and making personal care choices. The one area they can't touch is financial matters — paying bills, selling property, managing investments. That requires a separate Enduring Power of Attorney under different legislation.

Who Can Be an SDM (and Who Can't)

The Act sets clear eligibility rules. An SDM must be:

• An adult (18 or older)
• Someone who understands and accepts the role
• Someone who has signed the acceptance section on your ACD form

The Act also disqualifies certain people from being appointed:

• Paid professional carers — anyone who receives payment for providing you with personal care, nursing, or medical services
• Doctors and nurses — these professionals cannot be appointed as your SDM under the ACD rules
• The Public Advocate — while the Office of the Public Advocate provides dispute resolution and advocacy services, the Public Advocate cannot be personally appointed as an SDM

Beyond these hard disqualifications, there's an important practical constraint: anyone you appoint as SDM is automatically disqualified from also witnessing your ACD. So if you were planning to have your trusted nephew both serve as your SDM and witness the signing, you'll need to find a separate witness.

How Many SDMs Can You Appoint?

You can appoint up to four SDMs directly on the primary ACD form (the redesigned March 2024 version). If you need more than four — unusual, but possible for people with large families or complex circumstances — there's a supplementary form you can annex to the main document.

You specify the order of preference:

• First preferred — your primary decision-maker
• Second preferred — steps in if the first is unavailable, unwilling, or lacks capacity themselves
• Third and fourth — sequential backups

You can also impose conditions or limitations on any SDM's powers. For example, you might authorise your first preferred SDM to make all healthcare decisions but restrict your second preferred SDM to accommodation decisions only.

Choosing the Right Person

The legal eligibility test is straightforward. The harder question is whether your chosen SDM will actually carry out your wishes under pressure.

They need emotional resilience. An SDM may need to tell doctors to stop treatment. They may need to override the tearful objections of other family members who want "everything done." That takes a specific kind of strength — not callousness, but the ability to honour your wishes even when it's agonising.

They need to understand your values. The best SDM isn't necessarily the person closest to you emotionally. It's the person who most clearly understands what quality of life means to you — where your boundaries are, what conditions you'd find unacceptable, and what trade-offs you're willing to make between treatment and comfort.

They need to be reachable. In a medical emergency, the clinical team needs to contact your SDM quickly. If your first preferred SDM lives overseas or works in a remote location with limited phone access, that's a practical risk. Making sure at least one of your backup SDMs is geographically close and reliably contactable matters.

They need to be willing. Being asked to serve as an SDM is a serious request. Some people don't want the responsibility, and that's legitimate. Each SDM must sign the acceptance section on your ACD form — that signature is a legal acknowledgment that they understand and accept the role. Never assume someone will agree; have the conversation first.

The Signing Protocol That Trips People Up

The most common reason ACDs are invalidated in South Australia is a signing sequence error. The rules are rigid:

1. SDMs sign first. Every appointed SDM must complete and sign their acceptance section before you (the principal) present the document to the witness.
2. You sign before the witness. Once all SDM signatures are in place, you sign the ACD in the physical presence of an authorised witness.
3. The witness signs. The witness confirms that you understood the document, were acting voluntarily, and appeared to have decision-making capacity.

If the witness signs before all SDMs have accepted, the execution is invalid. You'd need to start over with a new form.

Since the March 2024 amendments, SDMs can use digital signatures for their acceptance sections. This is a genuine practical improvement for families where the appointed SDMs live in different cities or states — they can sign electronically and return the form before the principal completes the in-person witnessed signing.

What Happens If You Don't Appoint an SDM

You can complete an ACD that only contains instructions — no SDM appointments. Your documented wishes still have legal force.

But if a situation arises that your written instructions don't specifically cover, and you've lost capacity, the system falls back to the "Person Responsible" hierarchy in the Consent to Medical Treatment and Palliative Care Act 1995 — a SACAT-appointed guardian, a prescribed relative with a close and continuing relationship, an adult friend with such a relationship, or the person responsible for day-to-day care. SACAT may be involved as a tribunal of last resort.

Appointing an SDM is the mechanism that keeps control within the people you've chosen, rather than the people the statute defaults to.

Our South Australia Advance Directive & Living Will Kit includes an SDM appointment worksheet that walks you through the selection process, defines the scope of each appointment, and ensures the signing sequence is correct the first time — so the people you trust are the ones making your decisions.

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