# PEEP with a BVM



## exodus (Oct 24, 2011)

Can anyone explain how this valve work? I was under the impression that PEEP kept pressure on the airway at all times, how is that possible if the only time pressure is going through is as we squeeze the bag? I looked on google and couldnt find an explanation of how they work.


----------



## Handsome Robb (Oct 24, 2011)

You put the PEEP valve on the exhaust port of the BVM. It works just like any other valve, a spring holds the selected pressure against the valve. While the patient exhales they must consciously apply force to their exhalation in order to reach and maintain the pressure required to open the valve and allow air to escape thus creating positive pressure in the airway.

PEEP = Positive End Expiratory Pressure. CPAP = Continuous Positive Airway Pressure. You can use a PEEP valve to cause positive airway pressure not only during inspiration from the force of the bag being compressed but to also have the positive pressure on exhalation as I explained above.

I hope this makes sense, it's late so it might not haha.


----------



## exodus (Oct 24, 2011)

NVRob said:


> You put the PEEP valve on the exhaust port of the BVM. It works just like any other valve, a spring holds the selected pressure against the valve. While the patient exhales they must consciously apply force to their exhalation in order to reach and maintain the pressure required to open the valve and allow air to escape thus creating positive pressure in the airway.
> 
> PEEP = Positive End Expiratory Pressure. CPAP = Continuous Positive Airway Pressure. You can use a PEEP valve to cause positive airway pressure not only during inspiration from the force of the bag being compressed but to also have the positive pressure on exhalation as I explained above.
> 
> I hope this makes sense, it's late so it might not haha.



I get it, so on a basic level, it's imitating the pursing of lips on respiratory patients, keeping the alveoli open?


----------



## MSDeltaFlt (Oct 24, 2011)

exodus said:


> I get it, so on a basic level, it's imitating the pursing of lips on respiratory patients, keeping the alveoli open?



That is exactly what it's like. Definitely not true PEEP as on an ICU ventilator, but it is better than nothing and does improve oxygenation.


----------



## exodus (Oct 24, 2011)

Another Q, on a patient in resp arrest, what's causing the air to come back out against the force of the peep valve? Simply air pressure alone?


----------



## usalsfyre (Oct 24, 2011)

The pressure on the inside of the chest is higher than atmospheric air, therefore, diffusion happens.


----------



## BLS Systems Limited (Dec 9, 2011)

As a maufacturer of PEEP valves, there is a slight difference between pursed lip breathing and the spring loaded PEEP valve (although the owner of my company and inventor of one type designed his after a physician asked for a device that would mimic pursed lip breathing).  Pursed lip breathing creates an orifice which provides back pressure.  The resulting PEEP is affected by flow changes and/or changes to orifice size.  The spring loaded PEEP valve is known as a threshold resistor where the spring or springs press on the exhalation valve, which opens and closes based on the pressure differential between the airway and atmosphere.  Back in the day, they used water columns where "cmH2O" were actual water columns measured in centimeters.  You can still see some chest tube setups that use water columns to set the vacuum/suction level. You have to overcome the pressure caused by the weight of water to vent.

Regarding air movement, it always travels from high pressure to lower pressure.  Normal breathing is based on generating negative pressure in the chest, drawing in air. On exhalation, chest wall recoil increases the pressure above atmosphere, we open the epiglottis and air moves out to equal the atmosphere or pressure valve setting.  During mechanical ventilation (BVM or vent), we provide positive pressure upwards of 60 cmH2O to push air in.  We allow it to escape via natural recoil of the chest wall.  The positive pressure can be very damaging and many users are moving towards adult BVM's with pressure release valves similar to those on neo and ped bags.

One note you may want to consider, autoPEEP can be very negative outcome when bagging an asthmatic or COPD'er.  That's caused by giving a breath before they have exhaled fully.  The pressure may not be detected at the vent/BVM, but its higher in the lungs due to air trapping.  Here's a clue...if you hear wheezes at END-EXHALATION, there is air still trying to move out.  Be careful when forcing more air in as you can over-distend the lungs and cause a pneumo.


----------



## usafmedic45 (Dec 9, 2011)

exodus said:


> Another Q, on a patient in resp arrest, what's causing the air to come back out against the force of the peep valve? Simply air pressure alone?



As USALSFYRE pointed out the higher air pressure within the chest (or more accurately, the pressure gradient between the airways and the atmosphere) and also the natural elastic recoil of the chest wall. 



> The pressure may not be detected at the vent/BVM, but its higher in the lungs due to air trapping.



The elevated mean airway pressure and peak airway pressures (assuming volume controlled ventilation) would be good indicators if the patient were on a real ventilator.  However, I do agree with your point regarding the issue with BVMs and what passes for a "ventilator" in the field. 



> During mechanical ventilation (BVM or vent), we provide positive pressure upwards of 60 cmH2O to push air in.



I can understand that in unmonitored BVMs, but I've seldom seen purposeful tolerance (outside of extreme ARDS, etc where you really have run out of any other options) of such high peak pressures.  It's usually a fairly good sign that either the RT's hands are tied by an overbearing physician or that the RT needs to be retrained or fired.


----------



## BLS Systems Limited (Dec 9, 2011)

usafmedic45 said:


> The elevated mean airway pressure and peak airway pressures (assuming volume controlled ventilation) would be good indicators if the patient were on a real ventilator.  However, I do agree with your point regarding the issue with BVMs and what passes for a "ventilator" in the field.



One of the problems with most vent designs is the assumption that pressure within the system (and therefore display) is equal throughout (meaning that the pressure in the alveoli is the same as what's in the circuit up to the exhalation valve inside the ventilator).  We are in agreement with our thoughts, but I wanted to point out that any air movement within the patient/circuit reveals that there is higher pressure upstream of where the pressure manometer lies.  The highest grade of ICU vents can use esophageal pressure transducers to determine true intrathoracic pressures, where the lower end transport vents place a manometer in the circuit or even inside the vent unit itself.  Its the assumption that all is equal in the system is where we can run into trouble.  We have often been bagging someone and left a longer than normal exhalation phase only to see experience a looooong release of gas from the lungs.


----------



## usafmedic45 (Dec 9, 2011)

Tederator said:


> One of the problems with most vent designs is the assumption that pressure within the system (and therefore display) is equal throughout (meaning that the pressure in the alveoli is the same as what's in the circuit up to the exhalation valve inside the ventilator).  We are in agreement with our thoughts, but I wanted to point out that any air movement within the patient/circuit reveals that there is higher pressure upstream of where the pressure manometer lies.  The highest grade of ICU vents can use esophageal pressure transducers to determine true intrathoracic pressures, where the lower end transport vents place a manometer in the circuit or even inside the vent unit itself.  Its the assumption that all is equal in the system is where we can run into trouble.  We have often been bagging someone and left a longer than normal exhalation phase only to see experience a looooong release of gas from the lungs.



Point taken.  I wasn't sure how technical you wanted to get in this because after stuff like this comes up I usually get a few private messages going "What is....?".  That is one of the reasons why I tend to not put more technical information in my posts than I feel absolutely necessary to get the point across.  If people want to know more, they will most often ask for more information.

That's one reason why I've always argued that one of the key steps in assessing a high pressure alarm that isn't due to an obvious cause (coughing, etc), is often to disconnect the circuit and allow the patient to passively exhale.


----------



## mycrofft (Dec 9, 2011)

*Tracheal pressure may not equal bronchial or bronchiolar pressure.*

Consolidation, infection, COPD, penetrating trauma, infiltration could affect the sub-tracheal "downstream" pressures of segments of lungs. Maybe that's just a chalkboard distinction. I dread the field measures they would try to monitor that. 

How does ambient pressure, as with elevation gains or in aircraft, affect the picture?


----------



## BLS Systems Limited (Dec 9, 2011)

Ambient pressure affects things a great deal, depending on how you look at it.  A pressurized Learjet cabin may have an internal "altitude" of 6000' when flying at 37,000", which affects any gas occupying lesion such as bowel obstructions, closed pneumothoraces, pneumomediastina, etc.  In the event that we have to fly with a sea level cabin, we fly the plane at 25,000-28,000, which greatly affects the fuel consumption by 30%. 

It can also affect flowmeters since they are calibrated to 50 PSI gas source to room air, but at altitude, they can "under-read" due to lower gas density.  You really have to know why things work more than how things work in order to stay out of the weeds, including the mechanics of your equipment and patient.


----------

