Contributor: Dylan Luyten, MD Educational Pearls: Bag-valve masks (BVM) typically  have a port to connect O2 to. Unfortunately room air becomes entrained in the mask, reducing the FiO2 delivered to the patient. This can be overcome by using a PEEP (positive end-expiratory pressure) valve on the BMV  PEEP valves function by keeping alveoli open in the lungs at the end of expiration. This increases the oxygen diffusing ability of the lungs, keeping patients’ oxygen saturations higher.  Patients who are critically ill can become quickly hypoxic after RSI meds due to reduced functional residual lung capacity - an issue that can be overcome with a PEEP valve  PEEP also will reduce work of breathing in COPD and CHF patients References Bucher JT, Cooper JS. Bag Mask Ventilation (Bag Valve Mask, BVM) [Updated 2019 Jul 30]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441924/ Summarized by Will Dewispelaere, MS4 | Edited by Erik Verzemnieks, MD