Which of the following is a key component of a BVM?

A key component of a Bag-Valve-Mask (BVM) is the reservoir bag. The reservoir bag serves several important functions during ventilation. It allows for the storage of oxygen, enabling a lifeguard or medical professional to deliver higher concentrations of oxygen to a patient in respiratory distress. The reservoir bag also provides a source of positive pressure when squeezed, allowing effective ventilation of the patient's lungs.

In contrast, an endotracheal tube is utilized for advanced airway management rather than being a part of the BVM system itself. A suction unit is essential for clearing the airway but is not integral to the function of a BVM. Lastly, a pulse oximeter is used to measure the oxygen saturation level in the blood, providing valuable information regarding the patient’s oxygenation status but does not form part of the BVM setup. Thus, the reservoir bag is indeed the correct choice as a fundamental component of the BVM.