Final answer:
When a rescuer is untrained or not proficient, ventilations should be performed with caution to prevent harm. Proper training in CPR techniques is necessary for safety and effectiveness.
Step-by-step explanation:
Ventilations: When a rescuer is untrained or trained but not proficient, ventilations should be performed with caution to prevent harm.
Performing CPR without proper training can result in broken ribs or a broken sternum, causing additional damage to the patient. It is important to receive proper training in CPR techniques to ensure the safety and effectiveness of the procedure.