How can I monitor the member's loopback Interface (and service) ,when i use ltm npath mode?

How can I monitor the member's loopback port ,when i use ltm npath mode? ltm npath mode: https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/ltm-implementations-11-5-1/4.print.html ...