PO change order approval rules

Hello,

Business requirement is to trigger PO change order approval rules only when below changes occur:

• Change of Cost centre
• Increase of PO amount
• Change of supplier
• Adding PO line
• Change of description in PO line
• Change of item

Based on the fields availabe in FSM for PO approvals, I conclude below requirements can be controlled:

- Change of Cost centre 
- Increase of PO amount
- Adding PO line (it will increase the PO amount)

 

But I am unsure which parameters to use to trigger/route approvals for below changes:
- Change of description in PO line
- Change of item