Which modifier is typically not needed in addition to G9 for monitored anesthesia care?

The appropriate choice is B because the QS modifier is specifically used to indicate that a qualified anesthesia provider is present for a monitored anesthesia care service but does not include the entirety of anesthesia care. The G9 modifier is already inserted to designate that the procedure was performed on a patient with a significant medical history or other complicating factors.

When G9 is applied, it conveys that the anesthesia care is being modified due to the additional risks associated with the patient's condition. Since G9 already signifies that this patient's case is complex, there is no need for additional qualification with the QS modifier.

In contrast, the AD modifier denotes a medical direction relationship where the anesthesiologist supervises multiple anesthesia providers. The QX modifier indicates the services of a CRNA (Certified Registered Nurse Anesthetist) under supervision. Both of these contexts could coexist with G9, depending on the specifics of the case, and hence can be needed. Therefore, QS is not necessary in conjunction with G9, making it the correct choice in this scenario.