PA-Cs and NPs are working in the field of pain management but by definition they work under the supervision of or in collaboration with pain management physicians. To my knowledge there are no independently practicing interventional pain management NPs or PA-Cs. They simply do not have the procedure training or scope of practice rights.
The CRNAs are trying to expand their scope of practice illegitimately by seeking "advisory opinions" from state boards of nursing, most recently in Louisiana (read the bloated CRNA salary post for some details on that). Their efforts were shot down by the Louisiana supreme court but I am sure the battle isn't over.
This issue is not unique to CRNAs, other specialties are trying to bypass the legitimate pathways to expand scope of practice as well (podiatrists, optometrists, etc.). When their respective boards issue an "advisory opinion" saying that say "podiatrists are authorized to do knee replacements" (just as an example) then the medical community (orthopedists, AMA, etc) have to seek an injuction against them and proceed with an expensive litigation battle to halt this expanded scope of practice. You can read more about the defense of these issues on the AMA website because they are involved in this across a wide variety of specialties.
Unfortunately due to shrinking reimbursements in healthcare and pure greed, everybody is trying to expand their services (at the expense of quality to patients) to supplement their incomes. They focus on whether we (physicians) can prove that they are causing "harm" rather than using common sense to evaluate the quality of training. They ask patients to sacrifice quality of care to improve their access to care. There is a huge shortage of neurosurgeons but we don't see their quality of training declining, nor do we see Neurosurgery Assistants practicing independently.
Why anyone would accept this in anesthesiology or pain management is beyond my understanding, but it all comes down to the great motivator...money. Insurers and Medicare all want to cut spending and by destroying a medical specialty and renaming it a nursing specialty they can cut payments tremendously.
As a friend of mine says, "Everybody wants to be captain of the ship without going to captain's school."