What is an ME medical breath dryer?

An ME dryer is a short length of Nafion™ tubing with a protective outer braiding.

How does the ME dryer function?

As water vapor in breath travels through an ME Dryer, it is absorbed into the tubing and evaporates into the surrounding air. Conversely, this product will also function as a humidifier and add ambient moisture to dry cylinder gases. The amount of water vapor removed by or added to the tubing will depend on the relative humidity outside the tubing.

What are the benefits of using an ME dryer?

ME dryers prevent downtime of breath gas analyzers since the most common source of analyzer problems is condensable water vapor in the sample. Accuracy and precision of the analyzers also improve when water interferences are eliminated.

Where should the ME dryer be placed in the sample line?

When the dryer is located near the patient, the breath sample is still warm and will not have a chance to condense in the sample line. This placement is beneficial to the ME’s performance, as the water vapor transfer rate through the tubing increases at higher temperatures.

Should the ME Dryer be replaced after every procedure?

Since it is part of the sampling line, it should be treated as such. Some customers treat these dryers as disposable for hygiene reasons. The dryers are very durable and can theoretically be used for months without replacement. Each hospital, however, has its own guidelines and we defer to individual institutional policies.

Should the ME Dryer be replaced after every test?

ME Dryers are intended for single-patient use when used outside of the device. When used inside of the device or apart from direct contact with the patient, the replacement schedule will vary depending on the application. We recommend performing tests based on how the majority of your end-users are interacting with the ME Dryers and setting a replacement schedule. Another option is providing a single-patient use solution. Please reach out to us here to speak about both options with our team.

What happens when liquids and alcohols come into contact with the ME Dryer?

Because of the unique construction of the ME Series Dryers, Perma Pure strongly recommends against exposing the dryers to liquid water or alcohols. Both liquid types have the tendency to swell the dryers, possibly causing the material to deform and kink within the protection braiding during full contact, restricting gas flow and reducing drying performance.

In situations where these liquids are used, in order to limit the swelling effect, the exposure should be completed quickly and clean dry air should be used immediately following to quickly remove the moisture from the tubing.

Also, it is important to note that alcohol vapor will not impact the shape of the ME Dryers, but some of the vapor may contaminate the sample as it goes through the dryer.

What does discoloration of the Nafion™ Tubing mean?

Performance of Perma Pure’s Nafion™ tubing may decline over time due to buildup of residues. Perma Pure recommends replacing a worn tubing.

Nafion™ tubing will discolor over time in normal operation, turning yellow, then progressively darker. This is normal, and does not seriously affect performance. The following is a chart illustrating some of the common problems, their causes and Perma Pure’s recommended cleaning method. See the note below for the ME Series.

As you visually inspect* the Nafion™ Tubing element, account for the following observances.

Observance Likely Cause Repair Method
Collapsed Tubing Negative sample pressure Methanol
Black, Brittle Tubing Overheating Acid Wash may be used but it is probable that the element will need replacing and the temperature adjusted. Note Anodized Aluminum shell is recommended if dryer is to be heated.
Solid Deposits    
Yellow, waxy solids Ammonium salts commonly formed when ammonia is injected into stack gas exhaust as part of the DeNOx process. De-ionized Water
Red, green or blue deposits Indication of contamination with salts from corroded metal upstream of the dryer. Red for copper, blue or green for stainless steel (chromium salts). Acid Wash
Very, dark solids Most likely caused by oils or tars (residues of organic compounds) Acid Wash
Dark, Oily Liquids High-boiling liquid residues may be deposited within the dryer. Dark oily liquids are likely to be sulfuric acid residues. Acid Wash
Bent Tubing Twisting of element when assembling, disassembling or rotating fittings. Methanol
Broken Tubing Over-twisting of element, liquid water entering the tubing or excessive sample pressure and temperature None – replace with new dryer


*Although Nafion™ polymer is not hazardous, the nature of any sample residues within the dryer is unknown. Harsh solvent(s) are used to clean the Nafion™ tubing. Wear proper protective equipment, including at a minimum protective eyewear and rubber gloves. If acids are used to clean the tubing, a lab coat or coverall is recommended.

How do you treat collapsed tubing with Methanol?

When Nafion™ tubing comes into contact with an alcohol (i.e. Methanol), it will swell up to 188% of its original size, both in diameter and overall length. It is because of this characteristic that kinks in tubing can be repaired.

  1. Remove the coupling from the shell.
  2. Reinstall the element into the coupling only.
    1. Slide element into coupling through threaded end
    2. Push until snap ring seats
  3. Reinstall the front nut.
  4. Connect dry air to the sample inlet port, do not turn on flow.
  5. Gently apply methanol to the element, do not go closer than 1.5 inches from the header.
  6. Slowly begin to flow dry air through the tubing and allow to expand.
  7. If there are still collapsed sections, apply methanol to those areas while air is flowing.
  8. Once tubing is back to the proper shape, continue to flow dry air for several minutes.
  9. Proceed to Reassembly of the PD-Series Dryer.

How do you treat Nafion™ Tubing with an Acid Wash?

If oily residues are present, the dryer should be washed with acid to remove the residues and to recondition the Nafion™ polymer (restore it to its original sulfonic acid form).

  1. Prepare a bath of 10% nitric acid (HNO3) in a suitable container. The container should withstand exposure to nitric acid and heating.
  2. Immerse the Nafion™ tubing into the nitric acid bath taking care not to wet the epoxy headers. About 1.5 inches (4cm) of tubing as well as the header should remain out of the acid.NOTE: Do not sharply bend the Nafion™ tubing during this cleaning process. The bath should be large enough to allow the Nafion™ tubing to flex gradually. A magnetic stirring hotplate should be used if available. If not, the acid container should be heated in some fashion and stirred periodically.
    Caution: Heating of the acid bath will generate noxious fumes. The cleaning process should be performed in a fume hood or very well ventilated area. Covering the container with a loose plastic lid will minimize the fumes.
    Caution: Rubber gloves and protective eyewear must be worn. Nitric acid at this concentration will stain and/or irritate the skin and injure the eyes if splashed. 
  3. Heat the acid bath to 70°C to 80°C, and soak the Nafion™ tubing dryer element for one hour with occasional stirring (a magnetic stirring bar set on low if possible).
  4. Remove the dryer from the acid bath. The acid bath may be covered and reused until it shows significant discoloration.
  5. Rinse the outside of the tubing and headers with de-ionized (DI) water at room temperature to remove the nitric acid residues.
  6. Briefly force De-ionized water through the inside of the tubing. This may be accomplished with a plastic squeeze bottle or syringe. Do not immerse the headers of the dryer element in water or excessively wet the tubing inside the headers. Nafion™ tubing swells when exposed to water. If the tubing inside the epoxy headers becomes too wet, it may swell sufficiently to crack the rigid epoxy header.
  7. Quickly blow clean, dry air through the dryer element to remove any residual water.
  8. Continue to blow air through the dryer for several minutes. This will reduce any swelling and restore the dryer to normal length.

What are the advantages of an ME Dryer compared to a water trap or HME?

Simplicity – A water trap collects liquids that must be drained periodically. Since the ME dryer is removing water vapor, no condensate is formed, and the potential for liquid carryover is eliminated. Further there is absolutely no operator interaction or maintenance required. Performance – The breath sample at the outlet of a water trap is still saturated (100% RH), whereas the ME will reduce the sample humidity to room levels (generally 30-50%RH). Analytical Accuracy – Using a water trap for moisture removal in the presence of water soluble compounds such as NO2 causes sample integrity problems, since they can dissolve out in the condensate. An ME Dryer will selectively remove water vapor without affecting the gases being measured.

How should ME Dryers be stored?

ME Dryers should be stored in a cool, dark place. Exposure to light and heat can affect the aging of Nafion™ Tubing . We have seen color changes from almost clear to dark amber overtime, however, in our experience, we have not seen a significant change in performance. To discuss in more detail, you can contact our team here

Is a water trap or HME still needed?

No water trap is required to remove water. A filter to remove sputum is still desirable.

Can an ME dryer be sterilized?

The preferred method of sterilization is gamma radiation. Our recommendation is to utilize the dryer in the unsterilized condition and change it after each operation. If sterilization is desired, gamma radiation is the preferred method.

What is the size of an ME dryer?

The length of Nafion™ tubing required is determined by the sample flow rate and ambient humidity to which it is exposed. As a general rule of thumb, a 6″ dryer can be used for a sample flow rate of 75 cc/min and a 12″ dryer can be used for flows of 150 cc/min or less. Once the sample RH reaches ambient levels, moisture exchange ceases.

How cost effective is the ME Dryer?

Significant cost savings can be realized by the elimination of repairs and downtime of equipment caused by wet samples. No one can place a dollar value on preventing a gas monitor failure at a critical juncture during a medical procedure.

What can we expect when starting to work with Perma Pure on a solution?

Dedication to finding the best solution for your unique application, while maintaining high quality standards from design through delivery. You will have access to teams across our organization and we will engage with you to keep consistent alignment of product priorities and goals.

To learn more, please visit our Working Together page.

What is the proper disposal method for a used dryer?

The dryer can be disposed of using the same procedures as for any vinyl plastic components used in the hospital; land fill or special incineration. The product is very stable and will not decompose.

What testing capabilities are available for ME Dryers

We perform Leak, High Pressure, and Flow/Pressure Drop testing to ensure drying performance that meets your needs. Please contact our team here to learn more. 

What are the certifications for the ME Dryers?

We have regulatory experts in-house to ensure we remain certified and compliant with standards across the globe. On our ME Dryer product line, we maintain FDA 510K approval, ISO 9001 certification, and ISO 13485 certification. You can view all of our certifications here.

How is Drying Efficiency affected when ME Dryers are exposed to certain cleaning solutions such as Bleach, Alcohol, H2O2, Alconox, or NaCl?

In the past, tests were performed on the drying performance of ME Dryers before and after extreme exposure to all of the above substances. The ME Dryers were soaked in the substances for 24 hours and Drying Efficiency was examined before and after exposure. Prior to exposure, Drying Efficiency was between 87%  and 88% for all five substances. After exposure, Drying Efficiency for Alconox and NaCl shrunk to approximately 44%. For bleach and H2O2, Drying Efficiency was reduced to 33.62% and 63.76%, respectively. Alcohol caused complete occlusion. 

We are performing additional substance tests so we can increase our understanding of a wider variety of substances and their impact on ME Dryers. 


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