Education - The Science of HMEs

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Ancient man discovered medicinal plants by observation and experience.

Inhaling the smoke or odors of some plants was a frequent trial to get pleasure and relief of body troubles.

Nearly all respiratory troubles were treated by one form or other of inhalation.

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The highest achievement of progress of inhalation therapy began at the ninth century.

Arab physicians introduced many therapeutic agents to inhalation therapy.

The twentieth century witnessed the introduction of new therapeutic agents and higher technological devices for inhalation therapy.

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Drs. Starkey and Palen, 1888

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Treatment for respiratory ailments were common during the late 1800s.

This popular concoction claimed that it was not a drug but a “scientific adjustment to oxygen and nitrogen.”

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Indications for Compound Oxygen: Asthma Bronchitis Indigestion Hay fever Headache Rheumatism Neuralgia Diarrhea

…and cured none.

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In the 1940s in Chicago, Illinois, a group of oxygen-tank technicians began meeting with doctors concerned with lung disease.

This group named itself the Inhalational Therapy Association in 1946.

They gradually put together a series of classes for people administering medical gases to patients.

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In December, 1950, 31 members of the Association were issued certificates for attending 16 lectures.

This was the first certification of Inhalation Therapists. It was an on-the-job training system for so-called "oxygen jockies".

They had little formal education, but did have a desire to do their jobs better and help patients in the process.

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In the simplest of terms, humidity is the amount of water vapor that is present in the air at any point in time.

This can be expressed as absolute humidity, relative humidity or specific humidity.

Almost all weather reports generated anywhere in the world point out the percentage of humidity that is present in the atmosphere.

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Absolute humidity is the exact amount of water that is present in a given volume of air.

This gives a precise measurement of the amount of water present, and thus lets the experts calculate the percentage of humidity in the atmosphere.

Absolute humidity calculators specify the amount of grams of water vapor present in each cubic meter of air.

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Relative Humidity is the relationship between absolute humidity and the maximum humidity which gas can contain, expressed as a percentage, at a given temperature.

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Absolute humidity is the exact amount of water that is present in a given volume of air.

This gives a precise measurement of the amount of water present, and thus lets the experts calculate the percentage of humidity in the atmosphere.

Absolute humidity calculators specify the amount of grams of water vapor present in each cubic meter of air.

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Specific humidity is the number of grams of water vapor per kilogram of air.

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The Dew point temperature is the temperature at which the air can no longer hold all of its water vapor, and some of the water vapor must condensate into liquid water.

The dew point is always lower than or equal to the air temperature.

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The upper respiratory tract is lined by a warm, viscous mucous membrane.

As air passes over the membrane, heat and humidity is added to the inspired air before it reaches the lower airways and lungs.

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This membrane is lined with very small microscopic cilia which act as an airway protection mechanism.

The cilia’s constant movement is designed to expel any inhaled contaminants lodged in the airway.

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When a person exhales, the upper airway traps most of the heat and moisture in the exhaled breath so that it can be reused during the next inhaled breath.

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Your nose is responsible for about two-thirds of this process.

As the air passes further into your airway, it becomes warmer and more humid.

By the time air reaches your lungs it is at the ideal temperature and humidity.

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When you exhale your nose conserves water by recovering about a third of the moisture present in each exhaled breath.

That moisture is then used to assist in the humidification of your next breath.

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If you breathe through your mouth, you may develop a dry throat.

By breathing through your mouth, you bypass your nose, which is responsible for two-thirds of humidification.

This means that you've tripled the humidification workload of your upper airway.

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Even if you're only exhaling through your mouth, you are still losing valuable moisture.

You are not allowing your nose to recover the moisture your body invested in the air as you "inhaled" it.

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The blood in your capillaries meets the air and picks up the oxygen your body needs.

At the same time, the blood gets rid of the harmful carbon dioxide that your cells produce.

Some people think the lungs are just big hollow bags, but in fact they are more like sponges.

This increases the amount of area inside the lungs where the blood can meet with the air.

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Clinical uses for molecular water (humidity) can be divided into two broad classes:

1. To humidify dry, therapeutic gases to make them more comfortable to breathe.

2. To provide near body humidity levels of inspired gases for patients with artificial airways.

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1. Administration of medical gases from a cylinder or pipeline

2. Environmental R.H. < 70% in a patient with lung disease

3. Patient with known secretions or a disease that causes secretions

4. Anatomical humidifier is bypassed

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When the upper airway is bypassed, humidification during mechanical ventilation is necessary to:

1. Prevent hypothermia

2. Inspissation of airway secretions

3. Destruction of airway epithelium

4. Atelectasis

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This may be accomplished using either a heated humidifier or a heat and moisture exchanger.

HMEs are also known as hygroscopic condenser humidifiers or artificial noses.

The chosen device should provide a minimum of

30 mg H2O/L of delivered gas at 30°C.

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Heated humidifiers operate actively to increase the heat and water vapor content of inspired gas.

HMEs operate passively by storing heat and moisture from the patient's exhaled gas and releasing it to the inhaled gas.

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“This is to alert you that FDA has several reports of patient deaths and injuries resulting from malfunctioning volume ventilators and/or heated humidifiers.

One incident of fire, in which three patients died, is believed to have originated in either a Puritan-Bennett Cascade IA humidifier or in the Puritan-Bennett 7200 series ventilator to which the humidifier was attached.”

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Puritan-Bennett

Cascade Humidifier

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The only regulated parameter is the system’s temperature, not the humidity.

Temperature is used as a proxy for humidity.

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The optimal temperature setting at the proximal airway is recommended to be 37°C to 40°C (yielding 44 mg H2O/L of inhaled gas), but the scientific basis for this is debated.

As the gas travels through the circuit, ambient temperature changes cause the moisture to “rain out.”

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The condensation that develops presents a challenge to ventilator operation.

As it accumulates, the condensate must be disposed of in an aseptic manner.

Disconnecting the circuit to drain the condensate (“breaking the circuit”) may contribute to VAP and placement of an inline water trap may be an acceptable alternative.

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Use of heated wire circuits offers a partial solution to the condensation problem, as a temperature gradient is created by increasing the temperature in the distal aspect of the inspiratory limb.

Heating the interior of the circuit in this way greatly minimizes the rainout.

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The cost of a heated wire system is reported as a drawback to its use. If the circuit does not require changing, costs will decrease for each day it is used.

There are, however, operational issues that should be addressed.

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Temperature gradients:

To maintain optimal humidity delivery, gradients need to be adjusted as ambient temperature, ventilator settings, and water reservoir levels change.

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These settings will need to be changed if the patient is getting small volume nebulizer treatments; is in a room where temperature fluctuates (bedside fans or heating/air-conditioning problems).

It can be both intellectually challenging and time-consuming to have to adjust the equipment based on ambient conditions.

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Unfortunately, the concept of setting and adjusting negative or positive gradients is difficult for some to comprehend.

Setting these levels incorrectly with one system creates a new set of problems.

The alarms package in earlier versions of some devices was very sensitive, alerting the staff to problems very quickly.

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The audible alarms sound so frequently that there is a great temptation to either adjust the heater to a level that could be subtherapeutic or just turn it off.

Newer systems use compensatory algorithms to make these adjustments automatically, but in one study the devices produced humidity levels lower than advertised.*

*Lellouche F, Taille S, Maggiore SM, et al. Influence of ambient and ventilator

output temperatures on performance of heated-wire humidifiers.

Am J Resp Crit Care Med. 2004;170(10):1073-9.

Condensation from the patient circuit should be considered infectious waste and disposed of according to hospital policy using strict Universal Precautions.

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“HMEs should be used in all patients in whom there is no contraindication.”

Richard D. Branson MSc RRT FAARC

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June 2005Respiratory Care Journal

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The first heat/moisture exchanger, which was made of corrugated aluminum, was presented by a group of Swedish professors in the early 1960’s.

Due to its weight, the device never became widely used.

The market breakthrough for the artificial nose did not occur until the beginning of the 1970’s.

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The aluminum was replaced with a special paper in a corrugated structure with a large capacity for absorbing and giving off moisture.

Over the years the “noses” have been graduallydeveloped and the design has been refined.

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Heat and Moisture ExchangerNatural physical properties only

Hygroscopic Condenser Humidifier Enhancement of the natural physical properties

Calcium Chloride, Condensation, etc.

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There are 6 types of passive humidifiers.

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• heat and moisture exchanger

• least amount of moisture returned

H M E

• filtered heat and moisture exchanger

• second lowest amount of moisture returned

H M E F

• hygroscopic condensing humidifier

• second highest amount of moisture returned

H C H

• filtered hygroscopic condensing humidifier

• highest amount of moisture returned

H C H F

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• Gas flow may be altered

Bypass; BHME / BHCH

• Heat and water is added

Active; AHME / AHCH

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“The chosen device should provide a minimum of30 mg H2O/L of delivered gas at 30°C”.

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The patient has humidity and heat within their lungs. When the air or gas is forced out of the lungs, the PH collects or conserves that heat and humidity.

When this breath is exhaled, the gas passes through the PH and the heat and humidity or moisture is transferred to the PH.

When the second breath from the ventilator passes through the PH, it picks up heat and humidity from the PH and delivers it back to the patient’s lungs and so on.

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This continues and the patient’s moisture needs are meet.

Many products fail to meet the patient’s needs resulting in adverse events such as:

high pressure alarms, spontaneous pneumothorax, thick secretions, endotube occlusions, plugged airways, death and more.

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“Charging” is a function used by many manufactures to explain why their devices drain moisture from the patient’s breath.

“Coring” is the result from the charging process and the drying of the patient – the yellow spot on a cigarette filter is similar.

The longer you use this type PH, the more problems you will encounter.

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30/30 ?

INDICATIONS:

Humidification of inspired gas during mechanical ventilation is mandatory when an endotracheal or tracheostomy tube is present.

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CONTRAINDICATIONS:

Patients with preexisting pulmonary disease characterized by thick, copious, or bloody secretions should not use PH.

Use of an PH is contraindicated for patients with

an expired tidal volume less than 70% of the delivered tidal volume.

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“The chosen device should provide aminimum of 30 mg H2O/L ofdelivered gasat 30°C”.

30mg + 14mg = 44mg

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30/30

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Filter

Cost

Resistance

Moisture output

Dead space

Design

HMElowest

HMEF HCH HCHFhighest

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Most product literature today is misleading.

Resistance – wet? dry? first hour of use? last hour of use?

Does the device weight increase the longer it is used?

Does the moisture return remain constant over 24 hours of use?

Mg returned at what minute volume?

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Third party, third party, third party - but who funds the study?

Does the investigator have a financial interest?

In house studies are like calling your own balls and strikes.

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Any patient on a ventilator shall have30mg of moisture delivered at 300 C.

Spun Polypropylene/plastic - coated with CaCl-

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This is a question that all RCPs should ask themselves. It has certainly been asked by researchers.

Regardless of what type of system is being used, the clinician should question its effectiveness.

Since no system reports the actual amount of humidity being delivered, other signs must be relied on.

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Hygrometer will give baseline readings.

Observation of the circuit elbow itself between breaths for signs of small droplets of moisture.

Extra moisture condensation within the housing of the passive humidifier would be an indicator.

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Sputum evaluation.

How many HME change outs per day.

Viewing the circuit itself for signs of small droplets of moisture.

When heated humidifiers have been used, the presence of these small droplets in the chamber has been used as an indicator that the gas is fully saturated but...

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This is probably not an accurate method, since the temperature of the gas that leaves the ventilator can be quite high and will artificially raise the point at which condensation appears.

High or low ambient room temperature would influence the presence of moisture in the circuit.

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