Can spinal manipulation occur under anesthesia?

Yes, but. Yes this procedure has been offered, as to wether it works the jury is still out. Once you have been relaxed under general anesthesia you cannot stop or halt any damage to your skeletal system. This means if the chiropractor pushes too hard you will not be able to stop them i would discuss any MRI or ct showing the "need" for this with another md.
Spinal manipulation. Chiropractors do this and it's called mua. Before you consider this you must have probably an MRI of the part being manipulated and also discuss this with your pmd.