Wash. Rev. Code § 41.05.183
(1) Each employee benefit plan offered to public employees that provides coverage for hospital, medical, or ambulatory surgery center services must cover general anesthesia services and related facility charges in conjunction with any dental procedure performed in a hospital or ambulatory surgical center if such anesthesia services and related facility charges are medically necessary because the covered person:
(3) This section does not prohibit an employee benefit plan from:
[ 2001 c 321 s 1.]