Why do we have to put humidifiers or aerosol generators on 0₂ devices?

As the gas gets colder, it holds less water molecules. The partial pressure of H₂0 in the air goes down as the temperature goes down.  This is the principle behind rain following a cold front. The more water vapor in the warm air in front of the cold front, the more the water rains out of the air.

Heated air will hold a lot of water. This is the principle behind why Houston is so unpleasant in the summertime. Gas coming from a compressed gas system will be cold and dry. At the patient's mouth it is 21-22 degrees C--- So we add humidity to minimize the damage cool dry gas causes to the airway mucosa

Air inside the lung was heated to body temperature by the nose and less by the lower airways and is able to hold much more H₂0 than it did at room temperature.  If there was no water in the air stream, as it heats up from 22 degrees to 37 degrees, it picks up water molecules from the lung lining.

Secretions get thicker as water evaporates from the mucosa.
Patient loses body heat into cool dry air. This gets critical in the small infant.

Heated humidifiers have been used to speed up body heating in hypothermia. It is controversial just how much heated gas is needed.

Some feel that the gas should be heated to body temperature [37 degrees C] others say that we should over-heat the gas [40-45 degrees]

The principles behind this fact?

Relative humidity: it is known exactly how much water gas holds at various temperatures. The water molecules will evaporate as much as possible at  air temperature until it is saturated at that temperature but the absolute humidity varies.

RH of 100% at 21 degrees C is much less humidity than RH of 100% at 37degrees C because the absolute humidity differs drastically.
 

Absolute humidity: the exact mg/liter of water that is held by the air. The person who breathes 100% RH at 21 degrees will only have 18.4 mg/Liter of water, while the person who breathes 100% RH at 37 degrees C [98.4 degrees F] will have 43.9 mg/Liter of water in the air.  

Humidity deficient: the difference between what the gas holds at the nose and the amount of water the heated gas holds down in the air way is the deficient. This difference must be made up by evaporation of water from the body.  

At 21 degrees C the absolute humidity is 18.4 mg/liter and the body at normal body temperature of 37 degrees C needs 43.9 mg/liter. 43.9- 18.4 = 25.5 mg/liter of water will be pulled out of the mucosa. This is the humidity deficient

How does the humidifier operate?

Gas moves through a device and is exposed to H₂0 vapors so that it can pick up as much water vapor as possible. The speed of the gas flow, and its temperature will both alter the ability of a gas to saturate with 0₂ at that particular time.  

Humidifiers are rated for the flow rates they can accept, both for the changes in the ability of a given humidifier to add water effectively as well as the resistance to flow of the device. Both efficiency and resistance to flow are limitations of various types of humidifiers.  

The ability of water to enter the gas flow can be improved by the addition of more surface area for the gas and the water to interface for evaporation. Other humidifiers will use heaters to warm the air so that the gas will accept even more humidity.

 Cool Humidifiers

• Various types of cool humidifiers. There are four types of cool humidifiers for use with low flow 02 devices

• The bubble humidifier: the gas flow enters a tube to pass under the surface of the water. The gas bubbles pick up water vapor as they move upward toward the outlet.

• The bubble diffuser humidifier: a diffuser is added to the bottom of the tube to make the air bubbles that move through the water even smaller for increased surface area for water vapor to be added to the gas flow

• The jet diffuser: this device adds a jet below the surface of the water that will increase the gas flow and pull in more water for exchange. It still uses the diffuser down stream

• The jet humidifier: this device has a jet port above the surface of the water. As the gas velocity speeds up, water is drawn up a capillary tube to be shattered against a baffle, the water inside this device is suspended inside the reservoir as a mist that increases the relative humidity of the gas that passes through the mist.

Devices that operate with cool humidifiers. All these devices have small, thin 02 lines

• Nasal cannula

• Simple mask

• Non-rebreathing mask [if the pop off valve doesn’t alarm]

Devices that use a heated humidifier or an aerosol generator. All these devices have corrugated hoses attached to them called an aerosol hose.

• Tracheostomy collar

• Face shield

• Aerosol mask

• Brigg’s adaptor [T-tube]

The uses of bland aerosols [those that do not contain medication] include the delivery of sterile water, isotonic, hypotonic or hypertonic saline to the airways on a continuous basis with or without artificial airways

Bland aerosols may be given with Fi0₂ 0.21 or more

Bland aerosols may be given continuously or administered for 10 to 20 minutes at scheduled intervals

Indications for large volume aerosols
· Cool mist to the upper airways

• Via an aerosol mask or a face shield
  Post-op patients get cool mist to reduce the irritation that can result in swelling and edema from extubation. In this circumstance we use sterile water but sterile saline is less irritating to those who wheeze

• Croup, laryngitis or laryngotrachitis ----as long as they don’t wheeze.
  Induce coughing for sputum sample in persons whose secretions are too scanty to produce easily.

• Very common for cytology studies to find lung cancers.
  Hypotonic or hypertonic saline solutions are used to induce coughing because they are so irritating

Heated aerosols: Ideally once the patient’s airway has been bypassed, a heated aerosol might seem to be preferred to avoid the humidity deficient, but these devices can over-hydrate patients. More properly these folks might be better served with a heated high flow humidifier---but heated humidifiers are more expensive.

Cautions & contraindications to all types of aerosols but particularly cool ones

• Any aerosol that is not a bronchodilator has the potential to cause reflex bronchospasm.
   

• Aerosols carry microbes down to the lower airways

• They are associated with the spread of infections to caretakers [TB]

• They are irritating to some people

NOTE  Try to induce a cough without an aerosol first---you would be surprised how often no one has asked the patient to cough or no one has taught the patient how to cough into a sputum cup.
 

SOB--- Check the patient’s history for asthma or COPD before giving the standard 40%-60% aerosol, or if he presents with SOB, and wheezing after the addition of the aerosol, you should change 0₂ deliveries to device with cool humidifier.

Some facts about aerosol generators:

They create particles of water droplets

The 0₂ devices attached to aerosol generators have large aerosol hoses that will require draining every 3 hours. More often if heated aerosol

Fi0₂ adjustment on pneumatic aerosol generators [the most common] are forms of entrainment devices-like the entrainment mask.

As the Fi0₂ is raised the total flow rate to the patient drops.
As Fi0₂ drops the total flow rate increases.

The ratio is identical to that of entrainment mask [venturi-mask]

As water builds up in the tubing, there is increased pressure inside the entrainment device so that the lateral pressure rises and less air is entrained.

The 0₂ delivery devices all share the same generator and entrainment port, but the actual interface [Brigg’s adaptor, aerosol mask or face shield] has its own entrainment problems so the delivered Fi0₂ can vary.

Fi0₂ on these devices will vary from 0.28 to 1.0 based on the actual entrainment ports of the aerosol generator

Heated humidifiers

When do we use the heated humidifier?

• This is the humidification of choice:

• for the person on mechanical ventilation. We never use aerosols [heated or cool] on ventilators

• persons on cool aerosols who begin to cough or wheeze with the cool mist

• all persons with fluid retention problems can develop problems, particularly infants and small children who can quickly become fluid overloaded.

• Newborn infants. If the baby is small enough to be placed on a warmer or in an isolette he needs heated humidification---not cool aerosol.

• persons with artificial airways whose cough is ineffective, use care with the addition of heated or cool aerosol because the sudden thinning of secretions can occlude their airways.

• These persons frequently require less suctioning if they are given heated humidifiers rather than heated aerosols.

Heated high flow humidifiers are capable of delivering a high gas flow at or near body temperature at a RH of 100%. These are used with the ventilators and with the same devices that one would use a large volume aerosol generator with the exception of the tot hut and the 0₂ tent

• Heated humidifiers are used with artificial airways

• Any time that a heater is used there must be an air temperature probe or a thermometer at the patient's end of the tube.

• The thermometer should be accurate within +/- 3 degrees

• The RCP should chart not only the Fi0₂ and the set flow rate [on the flow meter] but also the temperature.

• The temperature should able to get to at least 30 degrees C [best is 32-34 degrees C ]

• Should alarm at 40 degrees or more

Other aspects of the heaters

Servo-controlled heaters have two thermometers. One at the outlet of the heated humidifier and one at the patient interface. These exchange data and the heater is increased or decreased based on their data.

·      Getting the sensors wet will cool them off and they may not work properly

o    Pull them out and dry them off

o    Try to keep the thermometer probe above the gas flow rather than on the bottom where water can collect

·      Servo controlled heaters can be used with heated wire circuits but these are usually limited to use with newborns who absolutely must have exact temperature control

·      This heated wire will limit rain out of cooled-off water from the circuit

o    Works well in neonatal circuits and one need only drain the hose two or three times a shift

o    Very expensive

o    Adult circuits that use heated wires will still have to be drained every 3 hours. To some this is rarely worth the money

·      Some heated humidifiers have a water line for constant feeding of water into the reservoir

• Others may have water lines that need to be opened by the RCP periodically.

• Increased chance of infection if the RCP has to open the reservoir to add water

• The concha ^TM heater has a water jug that holds about 24 hours worth of water, that constantly drips into the concha ^TM column's wick.
   

Some thoughts about the hose

All hoses that come from heated or cool aerosols or from heated humidifiers will have to be drained every 3-4 hours. If heated aerosol, check every 2 hours   

One can put a water trap into the line to collect rainout. Water traps must be placed in a dependent portion of the hose so that water drains into the trap. Full water traps get heavy so support it and drain it frequently. One popular water trap can be attached to wall suction so that the water is not a source of infection for the caretakers

Failure to drain hoses will :

1. Put the patient at risk of drowning in the water

2. Carries infection to the patient

3. Will decrease the flow of 0₂ to the patient

4. Will interfere with the Fi0₂ of the entrainment device upstream

How should the RCP chart 0₂ that is attached to a heated humidifier or heated aerosol?

Chart every 3 to 4 hours. Drain the hose first then listen to the patient’s chest [full hoses will mask breath sounds or even mimic rhonchi]

Chart the breath sounds, the respiratory rate and any interventions of yours such as adding water, suctioning the artificial airway or hyperinflation by bagging.

Chart the HR, and Sp0₂ when available

Check and chart the set flow rate as well as the set Fi0₂

Check and chart the temperature at the airway

Various types of heated humidifiers:

There are 5 types of heated humidifiers for high flow 0₂ devices

Heated Passover humidifiers: gas goes into the device and flows over the top of the heated water. Water vapor rises and is carried to the patient. The heater is an immersion heater. Very common with 0₂ hood for babies

Heated bubble humidifier: similar to the bubble humidifier except a heater is added.

Cascade humidifier: a variation of the bubble diffuser in that the grid breaks up the bubbles that go thought the heated water. Cascade I & II are examples

Wick type humidifier: a variation of the pass-over heater in which the gas enters a column that is lined by blotter paper soaked in water. There is more surface area available for the passing gas to pick up water. The column or the water may be heated.

Vapor phase humidifier: a hot plate heats up the water from below, then the hydrophobic filter allows only water vapor to pass into the gas stream

How does the aerosol generator operate? List the different types and compare each.

Large volume aerosol generators create particles of water with various means.
All aerosol generators must have sterile water or sterile saline

Pneumatic jet aerosol generator: most common

Gas flows along a tube with a jet so that entrainment of water is possible from the capillary tube rising from the water reservoir

• If there is a baffle the generator is a nebulizer

• If there is no baffle it is an atomizer

Baffles breaks up the particles into smaller particles, and the more baffles in the system the smaller the particles 

The average particle size is 2-20 microns with a total output of 30-50 mg/ Liter

½ of the particles will be in the 2-4 micron range so that they will rain out in the conducting airways
 

Mainstream: main flow of gas passes through the jet
Side stream: jet assembly is created then passed into the mainstream

Other facts about the pneumatic jet

Most operate at 8-12 lpm and use entrainment ports to control Fi0₂

The same jet stream that entrains water from the capillary tube frequently will entrain air into the 0₂ flow

Heaters can be added to the pneumatic jet to increase delivered fluid

• Usually emersion heaters

• Jacket heater or heater collar

• Sometimes hot plate

This is the most common means of 0₂ delivery for aerosol mask, face tent,  Brigg's T adaptors & trach collars

Ultrasonic nebulizer

These devices are rarely used for continuous deliver of gases, rather they are used to deliver sterile water or saline for scheduled treatments of 10-20 minutes

Ultrasonic nebulizers put out 1-10 micron sized particles [average 3 microns] with an output of 60-100mg/liter

The ultrasonic operates on the following principles

Electric energy goes to the piezo-electric transducer

The ceramic transducer vibrates to produce ultrasonic waves that creates a geyser of aerosol in the center of the couplant. Couplant water never touches the patient so it can be tap water. Couplant water must contain electrolytes so it must not be distilled water.

Immersed in the couplant water is a thin walled solution cup that carries sterile water or med

The vibrations continue up the water into the sterile solution above so that it too vibrates

Never put your finger in the water because you will get burned

If the machine fails to create mist, check the couplant water level. All metal parts should be underwater [electrodes] so that the electrical impulses can travel

The mist going to the patient is NOT hot, but the water in the couplant will burn you.

You want to see a nice geyser in the center of the couplant, just above that you should see the mist

Ultrasonic aerosol will stay inside the solution cup unless it is pushed out by a external fan or by the addition of compressed air or supplementary 0₂

Ultrasonic aerosol mist is a very small and very stable particle

Identify the quick method to tell if a device uses a cool humidifier or a heated humidifier or an aerosol generator.

Look at the line:

• Is it a thin 0₂ line? Then it can only handle a low flow, so use cool humidifier

• If it attaches to a large aerosol hose with a 22 mm diameter, the devices uses higher flow rates and it needs a heated humidifier or aerosol generator

Look at the outlet.

• If you see a visible mist no matter how small, it is an aerosol

• If you feel the gas but see nothing it is a humidifier that carries only water vapor

A quick word about room humidifiers

Room humidifiers are used to increase the relative humidity of the room. Because we put tap water into these devices, they should never be placed where the mist hits the patient's face---- rather aim it at the room. Many of these are not true humidifiers because most of them send out particulate water. Only the old fashioned steam vaporizer and the new wick room humidifier actually sends out water vapor. 

NOTE: recently, the EPA has suggested we fill the room humidifier with distilled water because the minerals found in tap water get aerosolized and this could be a health hazard.  

The EPA also recommends that we clean these devices with scrub brushes and a solution of 3% hydrogen peroxide every three days, as well as change out the water Q day. 

The EPA suggests we not raise the RH of the room any higher than 50% because that just encourages microbial/ mold/ bacterial growth. Unfortunately, RH that is comfortable for people is also more comfortable for bacteria. Asthma experts also caution asthmatics to avoid room humidifiers for this reason.

The most common room humidifier used in the hospital is the spinning disk nebulizer. The disk spins and pulls water up the hollow shaft where the water is slammed against the baffles by centrifugal force so that the particles are created. The fan blades create a wind current that moves the mist into the room.

Another type of room humidifier is the ultrasonic mist room humidifier which sends the mist not down an aerosol tube but into the room.

The old fashioned steamer/vaporizers are considered a danger around children because of the chance of steam or hot water burns.

There is a new room humidifier on the market that uses wick technology. According to the EPA, the advantage of this device is that as the RH in the room rises, the device pulls less water to evaporate on the wick—it is self regulating. It also transfers no particulate water which means less microbial contamination and less mineral deposits. This is a true humidifier like the old steamer/vaporizers.

Fi0₂'s and the flow rates possible with the following devices used to deliver 0₂ to the adult and the larger child:

• Face tents/ face shields

• T-tubes /Briggs adapters

• Trach-collars

These devices  can run off a heated humidifier, and could use an entrainment device to mix the air and 0₂ but they could also use an 0₂ blender to get the Fi0₂ exact.

When the heated humidifier doesn't use an entrainment device to mix the Fi0_2, the set flow rate and the delivered flow rate will be the same. The 0₂ delivery devices all share the same generator and entrainment port, but the actual interface [Brigg’s adaptor, or aerosol mask or face shield] has its own entrainment problems so the delivered Fi0₂ can vary.

Fi0₂ on these devices will vary from 0.28 to 1.0 based on the actual entrainment ports going into the heated humidifier [or aerosol generator]

Which of the above devices could be used to deliver an aerosolized medication if its hose was attached to a small volume aerosol generator [Nebulizer]?

Medication can be delivered via an aerosol mask, a Briggs's T-Tube or a Trach-collar. Everything that can be attached to a large aerosol generator can be attached to a small volume nebulizer. [SVN]

Indications, hazards and contra-indications, list the Fi0₂s and the flow rates possible with the following devices used to deliver 0₂ to the infant and the neonate:

• Mist tent/ croup tent/0₂ tent

• Tot hut

• Infant Hood

All three of these are enclosure 0₂ devices. These devices completely cover the patient's head or even his entire body. These are used in pediatrics because infants will not wear masks

The degree of control the RCP has over any enclosure 0₂ is based on the size of the enclosure, and the number of places where O₂ can leak out. Think of a car air conditioner and the central air conditioner of your house. Which works faster? The car's air conditioner, because the enclosure is smaller.

If the enclosure is small, there is a lot of control.
If the enclosure is large there is less control.

The Infant Hood:

0₂ hoods are indicated for delivery of 0₂ to the tiniest infants

It covers only the head. If the infant is small enough to need a warmer or an isolette to keep him warm, he needs this because his 0₂ will be delivered with fine control [+/- 2%] and fine control over the temperature.

This can be done with a hood because it is such a small enclosure so that the Fi0₂ on the blender can be adjusted by 1-2% increments

If there are heated wires on the humidifier, the temperature can also be controled to .5 degree with ease

Set average flow rates going into a 0₂ hood at 8-12 lpm.

The tot hut

The baby who is bigger but not big enough to roll over can be put under a tot hut. This is a soft plastic box that is assembled with wire corners and placed over the child's head. If small enough the baby's entire torso gets under the hut

Larger infants can get quite warm under these huts so heated aerosol may not be needed.

Flow rates need to be at least 12-15 lpm. Failure to keep flow high can result in the baby getting hot [even to the point of seeming to have a fever]

Fi0₂ is adjusted with entrainment device and as Fi0₂ goes up and the flow rate goes down some kids might get hot under the slower flow rates.

Mist tent/ croup tent/0₂ tent:

• are indicated for the delivery of bland aerosol and/or supplementary 0₂ to the larger infant.

• If the infant can sit up and stand up he is too big for the tot hut & is ready for the mist tent.

• Mist tents are attached to their own high flow rate, cool aerosol generator

• Fi0₂s are not easily adjustable because the enclosure is too big and too full of leaks for exact Fi0₂

• mist tents run off 50 psig

• if the mist tent is attached to a flow meter set the flow meter to FLUSH

• indication is for croup

• if the kid with croup doesn't need supplemental 0₂ one can attach this to compressed air to deliver the needed mist for croup

Mist tents are inappropriate 0₂ devices for newborns because [1] they are always cold and [2] because they are impossible to adjust the Fi0₂ to the exactness needed for a newborn

Compare the Fi0₂ selection that is possible with a 0₂ blender to those of an entrainment device.

• Blenders can deliver 0.21 to 1.0 Fi0₂ with 1-2% changes at each step.

• Entrainment devices will have a few preset values

• Both devices will have some added entrainment issues due to the interface

There will be no addition of flow to the blender. What you set on the flow meter is the actual flow

Which of these devices can be used to deliver the drug Ribavirin?

The SPAG unit can be attached to an 0₂ hood, a tot hut or can be put into a croup tent
While the product literature states it can be used with an aerosol mask, no self-respecting 2 year-old infant will wear an 0₂ mask without a fight---so  put them inside a croup tent.