Why shouldn't you use a pop-off valve for a pediatric Bag Valve Mask?

You should! Positive pressure ventilation is a poor substitute for normal respiration, even after an ET tube is placed, and with high flow 02 at 15LPM.

However, good basic BVM skills can save a patient and bad technique can sabotage a resuscitation. The Pop-off, or pressure relief valve, is present on all pediatric, and some adult BVMs. There is usually a disabling feature, often a bypass clip. The valve is included to ameliorate volutrauma and barotrauma when rescuers squeeze the bag too fast and forcefully. Unfortunately, other than routine intra-operative use in anesthetized apneic patients; when the patient ventilates easily with no resistance, the reasons we bag usually involve some measure of airway compromise, trauma, acute Asthma, airway obstruction, pulmonary edema, etc. and there is always adrenaline in terms of the rescuer performing the skill. It's easy to get carried away and use far too much force and volume. If the rate is too rapid this stacks breaths, which results in gastric insufflation even with Excellent mask seal and airway patency.

So to address your question; The pop-off valve is there to prevent some of the above. However, in some cases the pressure needed to ventilate adequately can exceed the pop-off pressure. When this happens with each ventilation, it becomes difficult to assess compliance and maintain consistant 'breaths'. In such cases, adjust the rate and volume. Lower volumes(400-600 mls or 'until adequate chest rise is observed') delivered over at least one second at a slightly faster rate of 12-15/min can reduce airway resistance. If the pop-off valve still triggers, disabling it can be lifesaving. For instance, it is often impossible to ventilate an apneic newborn without disabling the valve. Neonatal lungs may still be filled with amniotic fluid necessitating higher INITIAL ventilatory pressure than the 45cm/H20 the pop-off valve is set at...so using tiny volumes, visualizing chest rise, and maintaining a faster rate(40-60), a rescuer can feel the lung compliance improve as the fluid is displaced, and the airway pressures normalize.

One problem with disabling any safety feature is that the device is no longer 'safe'. So if a patient has a pneumothorax or major airway obstruction which is triggering the pop-off valve, once disabled, the increased ventilatory pressure can, and has, proved fatal. With field intubations, a triggering valve can be a valuable tool, alerting you to tube displacement, or a kink in the circuit.

The most important thing to remember about bagging is that it depends almost entirely on operator skill. Positioning of the head(sniffing), placing an OPA or NPA, suctioning, ensuring an inspiratory/expiratory rate of 1:2 can improve the quality of ventilations dramatically. Attention to airway patency, mask seal, chest rise, and optimal rate is key. It's a dynamic process, and the pop-off valve is just one component. Hope this answers your question.