To be effective, the agent must accept the appointment in writing. Subject to the right of the agent to withdraw, the acceptance creates authority for the agent to make health care decisions on behalf of the principal at such time as the principal becomes incapacitated. Until the principal becomes incapacitated, the agent may withdraw by giving notice to the principal. After the principal becomes incapacitated, the agent may withdraw by giving notice to the attending physician. The attending physician shall cause the withdrawal to be recorded in the principal’s medical record.