New Study Confirms Not All PEEP Valves Are the Same in Helmet CPAP
Aurika Savickaite
11/14/2026 Chicago
A new randomized crossover study in Respiratory Care finds that not all positive end-expiratory pressure, or PEEP, valves behave the same way during helmet continuous positive airway pressure, or CPAP. Flow-independent valves held pressure more steadily than flow-dependent valves, and healthy volunteers had to work harder to breathe with the flow-dependent type.
The takeaway for bedside teams is simple: the valve on the helmet's expiratory port matters. Two valves can be labeled with the same PEEP number and still produce different pressure swings and different work of breathing.
What the new study looked at
Sergio Lassola, Eleonora Balzani, Marco Casarotti, Riccardo Re, Silvia De Rosa and Giacomo Bellani enrolled 30 healthy volunteers in a crossover physiology study. Each volunteer used helmet CPAP with three setups, in random order: a flow-dependent, or V̇-dependent (V̇D), PEEP valve; a flow-independent, or V̇-independent (V̇I), PEEP valve; and a flow-dependent valve plus a 25-liter reservoir bag.
Each setup was tested at fresh gas flows of 80 and 120 liters per minute. The team recorded airway-pressure swings and nasal-pressure swings, used as a stand-in for inspiratory effort. The commercial valve models and the exact size of the pressure swings are not in the open abstract, so those numbers are not reported here.
What the study found
Flow-dependent valves produced significantly larger airway-pressure swings than flow-independent valves. Those swings were associated with greater inspiratory effort.
The difference in nasal-pressure swings, the effort marker, was clear at 80 liters per minute, where effort was higher with the flow-dependent valve. At 120 liters per minute, that effort difference disappeared, even though the airway-pressure swings were still larger with the flow-dependent valve. Adding the 25-liter reservoir bag only partly reduced inspiratory effort compared with the flow-dependent valve alone.
The authors concluded that valve type matters for pressure stability and work of breathing during helmet CPAP, and that raising fresh gas flow or adding a reservoir bag only partly offsets a flow-dependent valve.
What V̇-dependent and V̇-independent mean
The dotted V, written V̇, is the symbol for flow. In plain terms, the PEEP valve sits on the helmet's expiratory port and is what creates the pressure. Fresh gas flows into the helmet the whole time. When the patient inhales, some of that gas goes into the lungs, so less gas leaves through the valve. When the patient exhales, exhaled gas plus the fresh gas both go out through the valve, so flow through the valve rises.
A flow-independent, or threshold-resistor, valve is like a gate set to a number, such as 10 cmH2O. Once pressure reaches that set point, the valve opens and tries to hold that same pressure as flow changes with the breath. Pressure inside the helmet stays closer to the number you set, and the patient does not have to fight large swings.
A flow-dependent, or flow-resistor, valve behaves more like a narrowing in the tubing. Pressure is roughly resistance times flow. When flow through the valve falls during inspiration, helmet pressure can drop below the intended PEEP, and the patient has to pull harder. When flow rises during expiration, pressure can overshoot, which makes exhalation harder. An orifice, or fixed-orifice, valve is this kind of resistor. A high-efficiency particulate air, or HEPA, filter or a heat-and-moisture exchanger filter on the expiratory limb can act the same way.
Other names appear in the literature. Lassola and colleagues used V̇D and V̇I in the 2026 paper, and a 2025 commentary by the same group uses flow resistor and threshold resistor. A 2012 bench study by Stefano Isgrò and colleagues, and a 1986 Chest study by Banner and colleagues, use those same resistor terms. Water-seal valves are built as threshold resistors. Spring-loaded valves are also designed that way, but the label is not enough by itself.
In Isgrò's bench tests of 10 expiratory PEEP valves at flows from 30 to 150 liters per minute, precalibrated, or fixed, spring-loaded valves stayed flow-independent, even at high flows. Adjustable spring-loaded valves often did not. The VBM valve produced the largest error, with pressures up to 35 cmH2O at flows higher than 100 liters per minute. Some adjustable valves, even in the recommended 30 to 60 liters per minute range, generated pressures more than 3 cmH2O higher than expected. Some 15 cmH2O precalibrated valves delivered a PEEP 1 to 2.5 cmH2O lower than labeled. The water-seal valve was flow-independent in the usual clinical range and showed only a low degree of flow-dependence when flow exceeded 80 liters per minute.
Isgrò and colleagues concluded that adjustable PEEP valves are not suggested for continuous-flow CPAP systems, and that precalibrated and water-seal valves exhibit the best performance. They also stressed that delivered flow and pressure must be monitored.
What this means at the bedside
For nurses and respiratory therapists setting up helmet CPAP, the practical steps are straightforward.
Choose a precalibrated, fixed or water-seal PEEP valve when you can. Do not assume a spring-loaded valve is flow-independent unless it is a fixed, precalibrated model.
Measure pressure inside the helmet with a manometer. Do not rely only on the number printed on the valve.
If a HEPA or heat-and-moisture exchanger filter is on the expiratory limb, expect extra pressure, and more of it as flow rises. At lower flows around 60 liters per minute, that added pressure is often about 2 to 3 cmH2O. In a bench study by Rezoagli, Lucchini and colleagues, the median increase above set PEEP at 60 liters per minute was 2.2 cmH2O with no PEEP valve and 2.8 to 3.0 cmH2O with one of the two valves tested; the second valve added a median of 5.2 to 5.7 cmH2O even at 60 liters per minute. At 80 liters per minute the median increases were 3.9 to 7.7 cmH2O, and at 100 liters per minute they were 5.3 to 10.1 cmH2O, depending on the valve and the set PEEP. Check the manometer and titrate accordingly.
Keep fresh gas flow high enough to wash out carbon dioxide, as discussed in our post on dead space. The new volunteer study found that raising flow from 80 to 120 liters per minute removed the extra-effort difference of a flow-dependent valve, though pressure swings remained. A 2024 bench study by Coppadoro and colleagues, using fixed WhisperFlow valves, found the lowest extra inspiratory effort often at 90 liters per minute, and higher effort when flow was below peak inspiratory flow or when a HEPA filter was added. Titrate flow, and watch the pressure.
Teams should also know the valve that comes with a given helmet kit. In the 2025 commentary, Lassola and colleagues list the DIMAR PEEP valve as an example of a flow-dependent, orifice-type valve, and they name the Respironics WhisperFlow as a flow-independent spring-loaded example. Whatever the brand, confirm the pressure inside the helmet. Valve choice sits alongside other helmet-specific setup points, including the higher PEEP a good neck seal can hold, as discussed in our review of higher PEEP in ARDS.
Limitations
The Lassola 2026 study was done in healthy volunteers, not in patients with acute respiratory failure or ARDS. The exact pressure-swing numbers were not available in the open abstract. The Isgrò, Rezoagli and Coppadoro papers are bench studies. More research in patients is needed to know how large the effort difference is at the bedside, and which commercial valves were used in the volunteer study.
"Learning is the key for success with helmet CPAP, and that includes knowing your PEEP valve. Not every valve behaves the same way, and this new research is a good reminder to check the pressure inside the helmet," said Aurika Savickaite, MSN, RN, founder of helmetbasedventilation.com. [QUOTE FOR AURIKA'S APPROVAL]
Module 3 of the online course covers titration of PEEP, FiO2 and flow rate. Subscribe to our newsletter for new research and tips.
Related reading: Dead Space in Helmets Is a Fair Point, and It Has a Fix, Helmet-Based Ventilation Allows Higher PEEP With Minimal Leaks in ARDS, New Intensive Care Medicine Review Finds, Helmet NIV Success: Combining Knowledge and Experience, our FAQ and our Research list.
References
Lassola S, Balzani E, Casarotti M, Re R, De Rosa S, Bellani G. Impact of PEEP valve type on respiratory effort during free-flow helmet CPAP. Respir Care. 2026;71(11):1244-1251. doi:10.1177/19433654261455008
Isgrò S, Zanella A, Giani M, Abd El Aziz El Sayed Deab S, Pesenti A, Patroniti N. Performance of different PEEP valves and helmet outlets at increasing gas flow rates: a bench top study. Minerva Anestesiol. 2012;78(10):1095-1100.
Lassola S, Balzani E, De Rosa S, Turella M, Bellani G. Free flow helmet continuous positive airway pressure: the devil is in the "valve's" details! J Intensive Med. 2025;5(3):219-221. doi:10.1016/j.jointm.2025.03.003
Rezoagli E, Coppola G, Dezza L, et al. High efficiency particulate air filters and heat & moisture exchanger filters increase positive end-expiratory pressure in helmet continuous positive airway pressure: a bench-top study. Pulmonology. 2024;30(1):8-16. doi:10.1016/j.pulmoe.2022.05.003
Coppadoro et al. Not too much, not too little. Titrating flow rate to minimise inspiratory effort during helmet CPAP: a bench study. Pulmonology. 2024. doi:10.1080/25310429.2024.2411804
Banner MJ, Lampotang S, Boysen PG, Hurd TE, Desautels DA. Flow resistance of expiratory positive-pressure valve systems. Chest. 1986;90:212-217.
Tags: Helmet NIV, Helmet CPAP, PEEP, Research, For Doctors
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