Skyhawk5,

Excellent post, and good on you for bringing up the topic. I developed a paper on oxygen therapy almost two years ago to go along with the Supplemental User’s Guide to Oxygen Therapy (It’s available on OUCH). Part of that paper dealt with the need to inspect and test non-rebreather (NRB) masks on a frequent basis to ensure they are in top operating condition.  That paper also addresses why performing these inspections and tests are so important.  I’ve updated that part of the paper and included it below.  

Thanks again for starting a great topic like this.

Take care.

V/R, Batch

Why some cluster headache sufferers are unsuccessful in aborting attacks with O₂

Other than too low an O₂ flow rate, the single most common reason for cluster headache sufferers failing to achieve a successful abort on 100% O₂ is due to a malfunction of the NRB O₂ mask. Missing or malfunctioning exhaust check valves are one reason that causes NRB O₂ masks to malfunction.  A malfunctioning inlet check valve or one fouled by mucus is second reason. Missing or malfunctioning exhaust check valves allow ambient air to enter the mask.  This dilutes the oxygen concentration, increases the time to abort, and ultimately causes too many cluster headache sufferers to fail in achieving a successful abort.

A malfunctioning inlet check valve or one possibly fouled by mucus can create an even bigger problem as it allows exhaled breath to enter the reservoir bag.  As exhaled breath contains CO₂, and it enters the reservoir bag only to be inhaled with the next breath, the partial pressure of CO₂ (PCO₂) in the alveoli and bloodstream starts to increase.  If the one-way inlet check valve fails to seat properly when exhaling and continues to allow this to happen, the level of CO₂ recycled through the reservoir bag and into the bloodstream will build with each breath. This condition is called hypercapnia, and even a small increase of 0.25% in alveolar CO₂ levels will result in an uncontrollable increase in lung ventilation by 100%.  It should also be noted that an increase of CO₂ by as little as 1% of the inhaled breath acts as a powerful vasodilator even if the remaining 99% of the inhaled breath is pure O₂.  This can easily result in anxiety and possibly a sense of panic.  As hypercapnia is such a powerful vasodilator that it completely overrides the vasoconstriction caused by elevated levels of oxygen (hyperoxia). Unfortunately, this problem is one of the leading reasons why too many cluster headache sufferers are unable to achieve an abort with oxygen therapy and they abandon its use as an abortive.

This problem is more pronounced with the disposable NRB mask as the inlet manifold and check valve are located in a part of the facemask directly under the user’s nose.  For folks that get a juicy runny nose during their hits and oxygen therapy, it all collects on top of the inlet check valve.

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Disposable Non-Rebreather Oxygen Mask

All this points out the need for frequent functional tests of a standard disposable NRB O₂ mask’s exhaust and inlet check valves for proper operation.  It takes only a few seconds and it’s easy to perform. The following procedures will also work with the O₂PTIMASK™ offered by Linde LifeGas or the older Clustermasx™ with slight modifications.  They need to be inspected and tested as well but as their construction differs with both of the one-way intake and exhaust check valves located inside the “T” manifold as marked by the yellow tape indicating the direction of flow, these masks have far fewer problems.

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O₂PTIMASK™ System


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Clustermasx™

Obviously, functional tests and cleaning of your NRB masks should be accomplished between cluster headache attacks whenever possible.  This is particularly important for the disposable NRB masks as the exterior silicone exhaust flapper valves on these masks are easily dislodged and they can stiffen making a good seal difficult.  When this happens, it’s best to get a new mask rather than risk poor performance during oxygen therapy. They cost less than $2.  The disposable NRB mask should also be replaced if there’s any evidence of moisture inside the reservoir bag.  This can rapidly lead to the build up of bacteria given the high oxygen environment.

1. Testing the Exhaust Check Valves - With the supply valve on the O₂ cylinder closed, place the NRB O₂ mask on your face and inhale. Once the reservoir bag is tightly deflated, you should be unable to inhale any further and the mask should stay on your face without holding it in place. If this happens, the exhaust check valves and the mask face seal are functioning properly.  If you are still able to inhale and the mask falls away without holding it, one or both of the exhaust check valves are faulty, missing, or you have a poor facemask fit.  Inspect the exhaust check valves for cleanliness and presence of any foreign objects or mucus between the valve flapper and valve seat. This procedure also works if you’re using one of the new O₂PTIMASK™ systems from Linde LifeGas or one of the older Clustermasx™ configured with either the face mask or mouthpiece.

2. Testing the Inlet Check Valve – With the supply valve on the O₂ cylinder closed, and the reservoir bag deflated, place the mask to your face with your thumb and fore finger over the exhaust check valves on both sides of the mask and exhale. You should feel backpressure and the reservoir bag should not inflate. If this happens, the inlet check valve is functioning properly. If the reservoir bag inflates as you exhale, the inlet check valve is faulty. Inspect it for cleanliness and the presence of any foreign objects or mucus between the valve flapper and valve seat. If you have an O₂PTIMASK™ or one of the older Clustermasx™ place the palm of your hand over the exhaust port on the manifold and exhale. Again the reservoir bag should not inflate. Cleaning the check valves is easy, but not in the middle of a cluster headache attack.

If either the exhaust or inlet check valves fail on a disposable NRB mask during a cluster headache attack, all is not lost. There are simple workaround procedures that will allow you to continue oxygen therapy long enough for a successful abort. If one or both of the exhaust check valves are malfunctioning, place your thumb and forefinger over the flappers when you inhale and release them when you exhale. If the inlet check valve malfunctions, remove the mask from your face and exhale away from it to prevent CO₂ build up in the reservoir bag, then place the mask to your face to inhale. If you are using an O₂PTIMASK™ or the older Clustermasx™ and the exhaust check valve malfunctions allowing room air to enter the mask, place the palm of your hand over the exhaust port when you inhale and remove it when you exhale.  If you’re using either of these masks and the intake check valve malfunctions during oxygen therapy, inhale normally but move the mask or mouthpiece to the side and exhale around it.  This will prevent exhaled breath from entering the reservoir bag.

For the new folks unfamiliar with my background and who are probably wondering where all this information on oxygen masks and oxygen therapy is coming from, I’m a retired US Navy pilot with over 3000 hours flight time in Navy fighter aircraft and a degree in chemistry.  All of that flight time was spent breathing 100% oxygen from takeoff to touch down on missions lasting over two hours.  I’ll also add, frequently at flow rates well in excess of 25 liters/minute.  I also inspected my oxygen mask prior to every flight and once in the aircraft, I performed a functional check prior to starting the engine(s).  

Each year we were required to attend mandatory training in Aviation Physiology.  This training included classes in respiratory physiology where we received refresher training in blood gas chemistry and the latest changes in oxygen breathing systems.  Every two to three years or when we transitioned to a new aircraft, we were also required to make low-pressure chamber (LPC) runs where the chamber technicians reduced the pressure in the chamber equal to the pressure found at an altitude of 25,000 feet to re-familiarize ourselves with the symptoms of hypoxia (not enough oxygen).  

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Low-Pressure Chamber Hypoxia Training

Once we reached that altitude, we were required to remove our oxygen masks and perform a simple task of operating a piece of avionics, or sorting a deck of cards by suit.  As useful consciousness at this altitude is generally less than 2 to 3 minutes before hypoxia set in, few of us were ever able to completely accomplish the task before a chamber technician or Navy Corpsman stepped up and helped reattach our oxygen masks.  Navy and Marine Corps pilots and aircrews have been receiving scheduled hypoxia familiarization training in LPCs since 1941.

Don,

Thanks for the kind words...  Check your PM.

Take care,

V/R, Batch