This is probably more relevant to the OSCE but it may come up in the management.  The information is from here

• The person making the directive must be aged 18 yrs or older
• The person must be mentally competent when the directive is made
• The directive must specify the treatment refused
  • It may also specify the circumstances in which the refusal is to apply
• The person must not have subsequently withdrawn it or appointed an attorney to make the decision
• The person making the directive has not done anything inconsistent with the terms of the directive
• The individual lacks capacity to make decisions at the time the directive is invoked.

The directive must be

• Written down
• Clearly indicate that it is to apply even if life is at risk
• Signed and witnessed.