Do you suck or blow on green whistle for first aid?

The Green Whistle you are referring to is actually called Penthrox, and is an inhaled analgesia.

The "Green Whistle" would be prepared by an appropriately qualified professional, who would advise the patient on how and when to use it.

The patient would then breath in through the inhaler, 6 - 8 times, or until suitable pain management is achieved.