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This page describes products and general use; it is not medical advice.
An Ambu bag pop-off valve is the spring-loaded pressure-limiting valve fitted to some bag-valve-mask (BVM) resuscitators. It opens to vent gas when pressure in the device reaches a set level, so a squeezed breath cannot push airway pressure past that level. Not every resuscitator has one: in the Laerdal BAG II instructions for use, the infant and child units have the valve and the adult unit does not. It can also be overridden or locked, and published case reports describe the valve limiting ventilation when it was left active. (“Ambu bag” is used here as the common name for a BVM; Ambu is a brand. See what a bag-valve-mask is for the whole device.)
Who uses it: emergency medical services, hospital resuscitation teams and clinic staff who stock and check manual resuscitators, and students learning the equipment.
What an Ambu bag pop-off valve is
The pop-off valve (also called a pressure-limiting valve, pressure relief valve or pressure-limiting device) is a safety feature of some BVM resuscitators. A 2024 letter in Resuscitation Plus describes these valves as features that “may also mitigate the risks of excessive ventilation, particularly barotrauma”. Laerdal’s instructions for its BAG II resuscitator say the same of its valve: when it opens it reduces “the risk of stomach distension and / or barotrauma”. The search terms “pop off valve ambu bag” and “pop-off valve ambu bag” all refer to this one component.
How the pressure-limiting valve works
The same letter reports that the International Organization for Standardization (ISO) recommends BVM resuscitators have a mechanism to prevent airway pressures from exceeding 45–60 cmH2O, and that this is “typically achieved via a spring-loaded, pressure-limiting valve”. The letter cites ISO 10651-4 (user-powered resuscitators). It adds that pressure release systems must also meet minimum guaranteed tidal volume requirements, which balances adequate ventilation against lung protection.
In practice the valve works like this on the Laerdal BAG II: when resistance to the breath reaches the valve’s opening pressure, the device opens and a hissing sound can be heard. The manufacturer also notes that an abrupt, high-volume manual breath may still carry the unit above that level, so the valve is not an absolute cap.
Types and variants
Listings and instruction sheets distinguish resuscitators by whether the valve is present and whether it can be overridden. The rows below draw on the Laerdal BAG II instructions for use.
| Variant | What the source says | Key difference |
|---|---|---|
| With a pressure-limiting valve | Laerdal BAG II infant and child units have one that opens at approx. 35 ± 5 cmH2O | Vents gas at the opening pressure; hiss when it opens |
| Without a pressure-limiting valve | Laerdal BAG II adult unit: pressure relief valve listed as “Not provided” | No built-in relief at the bag |
| Overridable or lockable valve | Laerdal BAG II: override by depressing the plunger with light finger pressure, or lock with the push-twist feature | The valve can be held closed while the plunger is pressed or locked |
These are the variants of one manufacturer’s model. Other brands and models differ, so the instructions for use (IFU) of the exact product are the reference.
Pressure and specification values that matter
| Item | Value | Source |
|---|---|---|
| ISO-recommended airway pressure ceiling for BVMs | 45–60 cmH2O | Resuscitation Plus letter (2024), citing ISO 10651-4 |
| Laerdal BAG II infant (2.5–12 kg): relief valve | 35 ± 5 cmH2O nominal; max rate 180 bpm; tidal volume 180 ml (one-hand) | Laerdal BAG II IFU |
| Laerdal BAG II child (10–20 kg): relief valve | 35 ± 5 cmH2O nominal; max rate 144 bpm; tidal volume 330 ml (one-hand) | Laerdal BAG II IFU |
| Laerdal BAG II adult: relief valve | Not provided; max rate 85 bpm; tidal volume 830 ml (one-hand) | Laerdal BAG II IFU |
The gap between the 45–60 cmH2O standard figure and this model’s 35 cmH2O infant and child valve shows why a single “pop-off pressure” does not exist: the figure belongs to the specific product.
How to choose
The selection criteria that the manufacturer instructions support are these: check the product’s IFU for whether a pressure-limiting valve is fitted, at what pressure it opens, and how it is overridden or locked. Check whether the unit is single-patient use; the BAG II IFU states “single patient use only. Do not reuse. Do not sterilize.” Whether a pop-off valve is fitted differs by model and size, so the product listing and the IFU of that exact model should agree. Respiratory consumables are also listed under anesthesia circuits.
Safe use and handling basics
- Follow the IFU for the specific model, including the instructions for the valve’s override and locking features.
- The hiss heard when the valve opens is described by the manufacturer as the sign that it has opened.
- Single-patient-use devices are not reused or sterilized when the IFU says so; the IFU gives cross-contamination and performance degradation as the reasons.
- Training and local protocol decide how a valve is handled in a resuscitation. That is clinical guidance this page does not give.
Common mistakes
- Assuming every resuscitator has a valve. In the BAG II, the adult unit has none. The Resuscitation Plus letter also reports that, in the authors’ emergency service, paramedic awareness of these valves on adult BVMs and their practical implications was lacking.
- Treating the valve as a hard limit. The IFU states that an abrupt, high-volume manual breath may exceed the opening pressure.
- Overlooking the ventilation trade-off. The letter reports four patient safety events in one emergency service where a BVM with a pressure-limiting valve may have prevented adequate ventilation. In one case the valve was open with an air leak, and ventilation improved when the valve was closed (end-tidal CO2 55–65 mmHg afterwards). The authors write that the hazards of these valves impeding ventilation are long recognised, and that there is limited evidence linking high airway pressure alone with lung injury. Their service now requires valves to be closed during the initial phases of resuscitation. That is one service’s policy, not a general rule.
- Reusing a single-patient device. See the IFU statement above.
FAQ
Does every Ambu bag have a pop-off valve?
No. Some resuscitators have a pressure-limiting valve and some do not. In the Laerdal BAG II IFU the infant and child units have one and the adult unit is listed as “Not provided”. Check the IFU for the exact model.
What pressure does an Ambu bag pop-off valve open at?
It depends on the model. The Laerdal BAG II infant and child units open at approx. 35 ± 5 cmH2O. ISO, as reported in a 2024 Resuscitation Plus letter, recommends preventing airway pressure from exceeding 45–60 cmH2O.
Can the pop-off valve be closed or overridden?
On the BAG II, the IFU says it can be overridden by depressing the plunger momentarily with light finger pressure, or locked using the push-twist locking feature. Other models vary, so use the IFU for the product in hand.
Why does a pop-off valve matter?
It is intended to reduce the risk of stomach distension and barotrauma from excessive pressure, but published case reports show it can also limit ventilation if it opens when a higher pressure is needed or when there is a leak.
See also endotracheal tubes, ventilators, nasal cannulas and oxygen concentrators for related airway and oxygen equipment.
Sources
- Resuscitation Plus letter on pressure-limiting valves in bag-valve-mask resuscitators (2024), PMC11459487: https://pmc.ncbi.nlm.nih.gov/articles/PMC11459487. Checked 2026-10-29.
- Laerdal, The BAG II resuscitator, instructions for use: https://res.onemed.com/DK/IU/957731.pdf. Checked 2026-10-29. Values apply to this model only.
