When your patients feel dizzy during cervical extension, do you automatically panic and think it is vertebro-basilar insufficiency (VBI)? Well don’t! 
During my manual therapy training almost 3 decades ago, I was taught that vertebral artery tests could pick up VBI. Therefore, if the tests were negative, it was safe to perform cervical manipulations.
This latest systematic review suggests that “…cranio-cervical positioning may not alter blood flow as much as previously expected.”
Basically it is a waste of time and it does not rule out the risk of potential adverse effects following cervical manipulations. Therefore about 15 years ago, I simply stopped performing cervical manipulations.