Which is the first step when using a bag-mask device after positioning over the victim's head?

The first step when using a bag-mask device after positioning it over the victim's head is to place the mask on the victim's face. This step is crucial because proper mask placement is essential to create an effective seal over the victim's nose and mouth. This ensures that when you do give breaths by squeezing the bag, the air is delivered into the lungs instead of escaping around the sides of the mask, which could lead to ineffective ventilation.

Once the mask is securely positioned on the victim's face, other techniques such as using the E-C clamp technique can be employed to maintain the mask's position and seal. Only after the mask is properly placed can you proceed to give breaths and check for chest rise, ensuring that the breaths are effective. Proper order of steps is vital to ensure that the resuscitation efforts are as effective as possible.