I would advise that many insurances will not reimburse for CSA/LSA assistant at surgery. In fact, I am not aware of any that will, but I don't have firsthand knowledge for ALL insurance companies.
Modifier -AS is defined as Physician assistant, nurse practitioner, or clinical nurse specialist services for assistant at surgery.
CSA/LSA does not meet that definition, therefore -AS is not appropriate unless you have specific written guidance from the insurance stating it is their policy.
My own personal 2 cents from my experience:
Since PAs & NPs are reimbursed, and can also provide additional services like discharge orders, writing Rx, answering patient questions, postop care, etc., it is worth the additional salary expense for a PA/NP vs CSA/LSA for a busy surgeon. My surgeons can do an additional 2-3 surgeries each day by having the PA/NP handle these items for him.