1

Humidifier Moisture Exchange(HME) filters

University of Gondar

Department of Anesthesia

Girmay F.

girmaytg@yahoo.com

2

Presentation outline

1. What is humidity2. Role of Humidification Gas3. Measurement of humidity4. Methods of humidification 4.1. Heat & Moisture

Exchanger(HME) Filter

3

1. What is Humidity ?

Humidity is a measure of the amount of water vapour in a

gas/atmosphere .

1. Absolute humidity : is defined as

actual mass of water vapour present in a known volume

of gas.

o Usually expressed in either mg / L (Kg/m3,g/m3) or

mmHg (partial pressure).

4

the absolute humidity of air in the URT in humans is

about 34g.m-3 and it reaches a peak of 43g.m-3 as it

reaches the alveoli.

5

2. Relative humidity: the ratio of the mass of water vapour in

a given volume of gas to the maximum amount of water

vapour that the same gas can hold at the same temperature.

OR

Amount of water vapour in a gas, expressed as a percentage

of that which could be held by the gas if it were fully

saturated at the same temperature.

6

Relative humidity = Actual Water Content

H2O Content Fully Saturated %

OR

R.H. = Actual Vapour Pressure

Saturated Vapour Pressure %.

7

3. Dew point: The temperature at which the relative humidity of the air exceeds 100% and water condenses out of the vapour phase to form liquid .

4.Hygrometer : An instrument used for measuring the humidity of a gas.

5. Hygroscopic material: One that attracts moisture from the atmosphere.

8

2. Role of Humidification Gas

The air we breathe becomes fully saturated with water

vapour as it passes through nose to finally reach the

alveoli.

This humidification maintains

Mucosal integrity, Ciliary activity

Prevents the drying of secretions and helps in easy

expulsion of respiratory secretions when coughing.

9

Physiology of air way humidification

Nose breathing at rest ,inspired gases become heated at

36oc and are about 80% to 90% saturated with water

vapour by the time reach the carina. Largely due to heat

transfer in the nose.

Mouth breathing reduces this to 60 % to 70 % relative

humidity.

Heat and moisture content falls from carina to nares, so

that the nose typically at 30oC.

A countercurrent mechanism heat and moisture

exchange in the airways maximises

efficiency, with nasal cooling on

inspiration and warming on

exhalation.

Tracheal temperature and humidity fall with increased

ventilation particularly when the inspired

gases are cold and dry .

11

If totally dry gases were inspired and fully saturated

gases exhaled, the total water loss from ventilation at

rest would be about 300 ml/day in the average adult.

Normally about half is retained...30% by the nose

and 25% the humidity of inspired room air.

Bypassing the nose with an ETT and not humidifying

gases cases maximal losses.

12

Respiratory losses of both heat and water increase with

increased ventilation,

hyperthermia, and dry inspired

gases.

Cilia paralysis and reduced rates of mucus flow occur

below 50% relative humidity at 37 °C.

13

Lack of humidification (e.g. ventilating a patient with

dry gas through a tracheal or tracheostomy tube) can

result

in cracking of mucosa, drying of secretions

keratinisation of the tracheo -bronchial tree

Reduction in ciliary activity, atelectasis and

infection.

14

Over-humidification has its own complications.

It can result in water intoxication, especially in

neonates and infants in intensive care.

water clogging and airway burns.

15

Ideal properties of humidifier :

Efficient and easy to use.

have low resistance to flow of gas, and should be

economical and safe.

Humidification can be used with any breathing circuit and

may be provided for air, oxygen and a mixture of gases

including anaesthetic gases.

16

3. Measurement of Humidity

Measured using hygrometer ; most Measure

relative humidity

1. Hair hygrometer : This is based on the principle that the length of the

hair increases with increasing humidity.

It is fairly accurate between 30 and 90%.

17

2. Wet and dry bulb Hygrometer:

Two mercury thermometers, one in ambient temperature

and the other in contact with water through a wick are

used.

The difference in the temperature reading in these two

thermometers is a measure of rate of

evaporation of water, that in turn depends on

humidity.

18

3. Regnault’s hygrometer

• Air is blown through a silver tube containing Ether.

• At dew point , condensation occurs on the outer surface of

the tube. Ambient air is fully saturated at this temperature.

• The ratio of saturated vapour pressure (SVP) at dew point

to SVP at ambient temperature gives Relative humidity.

19

4. Mass spectrometer:

o This instrument uses the principle of reduction in the

ultraviolet light transmitted through the medium

containing water vapour.

20

4. Methods of humidification

Heat and moisture exchanger(HME) filter

Water bath humidifier

Nebulizers/ Nebulisers

21

4.1. Heat & Moisture Exchanger(HME) Filter

HME filters contain materials such as ceramic fiber, paper,

cellulose, fine steel or aluminum fibers in a hygroscopic

medium such as calcium chloride or silica gel .

1. Warm, humidified, expired gas passes through the HME,

water vapour condenses within the medium and is then re-

used for humidification of the inspired gas.

22

The HME is warmed by the latent heat of water

condensing on it. This heat is also released during

subsequent inspiration.

2. Minimize transmission of bacteria and viruses filtering

properties with efficiencies more than 99.9977.

They protect : patient, breathing circuit, anaesthetic

machine and ventilator.

23

The microbial filtering property may be due to:

1. Direct interception: If the particle is more

than 1µm (micrometer), it is physically prevented

from passing through the pores.

2. Inertial impaction :Smaller particles (<0.5µm)

are held by the filtering medium by van der Waals

electrostatic forces.

24

3. Diffusion interception: Particles less than

0.5mcm move freely and randomly (Brownian

movement) and subsequently swell up and get filtered

by the pores.

4. Electrostatic attraction: Charged particles

are attracted by oppositely charged fibres.

25

The main advantages of HME filters are:

Easy to use in breathing circuits.

Cheap and disposable.

60-70% relative humidity achieved.

Temperature achieved ranges from 29-34 BC.

Can be incorporated as a microbial filter.

26

The main disadvantages

Need replacing every 24 hours (maximum).

Secretions can block the filter.

Resistance to flow of gas can be up to 2cmH2O.

Can add to the weight of the circuit – may be

significant in neonates /infants.

Increase circuit dead space.

27

28

2 ports (tubing connections)

• sampling port for capnography

Filtration element :

Felt-like electrostatic material

Pleated hydrophobic material

29

Summery

HME filters and breathing system filters are intended to

replace the normal warming, humidifying and filtering

functions of the upper airways.

Humidity is an imp’t aspect of delivering gases to

patients in operating theatres and ICU.

The consequences of not humidifying gases can be

serious in particular patients.

30