Final answer:
In the case of cyanide exposure with inadequate breathing, using a bag-valve mask is the most recommended method of providing assisted ventilations, ensuring efficient oxygen delivery and rescuer safety.
Step-by-step explanation:
The most appropriate method of providing assisted ventilations to a patient who has experienced significant exposure to cyanide, is semiconscious and is breathing inadequately would be to use a bag-valve mask. This device allows for high concentrations of oxygen to be delivered, which is essential in the treatment of cyanide poisoning. Furthermore, mouth-to-mouth ventilations are not recommended due to the risk of contamination to the rescuer, and waiting for a paramedic unit to intubate could delay critical care. It is important to provide oxygen as efficiently as possible to a patient in this critical condition, while ensuring the safety of the healthcare provider.