Every bag-valve-mask ventilation depends on one thing: a good mask seal. Without it, air leaks out, and the patient gets less oxygen than you intended. Rescuers can build that seal in two main ways. One rescuer can use the E-C clamp, or two rescuers can split the work. This guide explains both techniques, compares them, and shows when a second rescuer makes the biggest difference. Why the Mask Seal Matters The bag-valve-mask, or BVM, delivers positive pressure ventilation. That pressure only helps if it stays inside the airway. A poor seal lets air escape around the mask. A poor seal is also one of the most common BVM mistakes, so technique choice matters. For a complete introduction to the device, see our guide to bag-valve-mask ventilation. The One-Person E-C Clamp Technique Sometimes you are the only rescuer. In that case, use the E-C clamp. Follow these steps: Position yourself at the top of the patient's head, and open the airway using the sniffing position. Use a jaw thrust i...