Cathedral vaulted or any ceiling that has insulation blocking the airflow from the soffit vents to the attic needs an attic baffle in each rafter bay.
Cathedral ceiling attic ventilation.
Depending on your house interior and roof framing design cathedral ceiling ventilation can be treated as an independent or attic ventilation related condition.
Without an attic baffle there will not be any air space for fresh air to enter the attic from the soffit vents.
As much as regular attic ventilation is an important part of your house maintenance routine and usually easy to perform cathedral ceiling ventilation maintenance might be difficult or even impossible to do.
Each slope of the roof is divided roughly in thirds by 3 different situations.
Proper ventilation is necessary in order to address water vapor that cannot be blocked to allow it to escape rather than allowing it to accumulate until it causes problems.
Here are some older home cathedral ceiling roof insulation and ventilation options that you may consider.
Reduce under roof insulation level to 3 fiberglass r 11 under the cathedral ceiling not good energy savings not recommended but functional just poor insulation value.