Presentor : Dr. kailash mittal

Moderator : Dr. M L Tak sir Dr.

Neelam mam

HUMIDIFIER AND SCAVENGING SYSTEM

HumidifiersHumidification is a method to artificially

condition the gas used in respiration of a patient as a therapeutic modality.

Active method is by adding heat or water or both to the device & passive which is recycling heat and humidity which is exhaled by the patient.

Indications of HumidificationPrimary:

Overcoming humidity deficit created when upper airway is bypassed

To humidify dry medical gases

Secondary:To manage hypothermiaTo treat bronchospasm caused by cold

air

Clinical signs and symptoms of inadequate humidification

Dry and non-productive coughAtelectasisIncreased airway resistanceIncreased work of breathingIncreased incidence of infectionThick and dehydrated secretionsComplaints of substernal pain and airway

dryness

PhysiologyHeat and moisture exchange is a primary

function of the upper respiratory tract, mainly the nose.

The nasal mucosal lining is kept moist by secretions from mucous glands, goblet cells, transudation of fluid through cell walls, and condensation of exhaled humidity.

As the inspired air enters the nose, it warms (convection) and picks up water vapour from the moist mucosal lining (evaporation).

Condensation occurs on the mucosal surfaces during exhalation, and water is reabsorbed by the mucus .

The mouth is less effective at heat and moisture exchange than the nose because of the low ratio of gas volume to moist and warm surface area and the less vascular squamous epithelium lining of oropharynx and hypopharynx.

As inspired gas moves into the lungs, it achieves BTPS conditions (body temperature, 37° C; barometric pressure; saturated with water vapor [100% relative humidity )

This point, normally approximately 5 cm below the carina, is called the isothermic saturation boundary (ISB).

Above the ISB, temperature and humidity decrease during inspiration and increase during exhalation.

Below the ISB, temperature and relative humidity remain constant (BTPS).

The ISB shifts distally :- when a person breathes through the mouth rather than the nose; when the person breathes cold, dry air; when the upper airway is bypassed (breathing through an artificial tracheal airway); or when the minute ventilation is higher than normal.

When this shift of ISB occurs, additional surfaces of the airway are recruited to meet the heat and humidity requirements of the lung.

These shifts of the ISB can compromise the body’s normal heat and moisture exchange mechanisms, and humidity therapy is indicated.

Principles of humidifier function

Temperature – As the temperature of a gas increases, its ability to hold water vapour (capacity) increases .

Surface area – There is more opportunity for evaporation to occur with greater surface area of contact between water and gas.

Time of contact – There is greater opportunity for evaporation to occur, when a gas remains in contact with water for longer duration .

Method of humidificationHumidifiersHumidifiers – –

a. Passive (Heat and Moisture a. Passive (Heat and Moisture Exchangers/ HMEs) – hydrophobic/ Exchangers/ HMEs) – hydrophobic/ hygroscopichygroscopic b. Active – unheated/ heatedb. Active – unheated/ heated

NebulizersNebulizers

PASSIVE HUMIDIFIERSSimplest designs are Heat and Moisture Exchangers

(HMEs)

Also called as condenser humidifier, artificial nose, Swedish nose, nose humidifier, regenerative humidifier, vapor condenser

Disposable devices that trap some exhaled water and heat, and deliver them to patient on subsequent inhalation (minimize water and heat loss)

When combined with a filter for bacteria and viruses called Heat and Moisture Exchanging Filter (HMEF) particularly important when ventilating patients with respiratory infections or compromised immune system

Exchanging medium

enclosed in plastic housing

Vary in size, shape, dead space, pediatric and neonatal HMEs with low dead space available

May have a port to attach gas sampling line for respiratory gas monitor

Placed between ET tube and breathing circuit

Hydrophobic HMEs –1.1. Hydrophobic membrane with small Hydrophobic membrane with small

pores, pleated to increase surface pores, pleated to increase surface areaarea

2.2. Allow passage of water vapour but not Allow passage of water vapour but not liquid water at usual ventilatory liquid water at usual ventilatory pressurespressures

3.3. Efficient bacterial and viral filtersEfficient bacterial and viral filters

4.4. Performance may be impaired by high Performance may be impaired by high ambient temperaturesambient temperatures

Hygroscopic HMEsContain low thermal conductivity wool ,foam or paper like material coated with lithium chloride or calcium – to recollect the moistureIn exhaletion: some vapour will condense and the rest will absorbed by hygroscopic saltInspiration: the low water pressure in the inspired air cause released the water molecule direct from hygroscopic salthigh efficiency compare to hydrophobic HMEsapproximately 70% efficiency that is 40 mg/l on exhaled, 27 mg/L on return

TypeType HygroscopicHygroscopic HydrophobicHydrophobic

Heat and moisture Heat and moisture exchanging efficiencyexchanging efficiency

ExcellentExcellent GoodGood

Effect of increased Effect of increased tidal volume on HME tidal volume on HME efficiencyefficiency

Slight decreaseSlight decrease Significant decreaseSignificant decrease

Filtration efficiency Filtration efficiency when drywhen dry

GoodGood ExcellentExcellent

Filtration efficiency Filtration efficiency when wetwhen wet

PoorPoor ExcellentExcellent

Resistance when wetResistance when wet Significantly Significantly increasedincreased

Slightly increasedSlightly increased

Effect of nebulised Effect of nebulised medicationsmedications

Greatly increased Greatly increased resistanceresistance

Little effectLittle effect

ideal HME should operate at 70% efficiency or better providing at least 30 mg/L water vapour.

Advantage: inexpensive easy to use Small and lightweight silent in operations do not required water, temperature monitor, alarms No burns, no danger of over hydrations and electric

shock.

Disadvantages:

less effective than active humidifiers can deliver only limited humidity increased in dead space (Boots et al 2006) Need change the HME every 24(Boots et al 1993)

or 48(Djedaini et al 1995)

Contraindications For patients with thick, copious, or bloody

secretionsFor patients with an expired tidal volume

less than 70% of the delivered tidal volume (e.g., patients with large bronchopleural fistulas or incompetent or absent endotracheal tube cuffs)

For patients whose body temperature is less than 32° C

For patients with high spontaneous minute volumes (>10 L/min)

ACTIVE HUMIDIFIERSAdd water to gas by passing the gas over a water

chamber (passover humidifier) or through a saturated wick (wick humidifier), bubbling it through water (bubble-through humidifier), or mixing it with vaporized water (vapour-phase humidifier)

Unlike passive humidifiers, they do not filter respiratory gases

2 types – 1. Unheated2. Heated

UNHEATED HUMIDIFIERS bubble-through devices used to increase humidity

in oxygen supplied to patients via facemask or nasal canula

Simple containers containing distilled water through which oxygen is passed and it gets humidified

Maximum humidity that can be achieved is 9mg H2O/L

HEATED HUMIDIFIERS Incorporate a device to warm water in the

humidifier, some also heat inspiratory tube content -Humidification chamber – transparent (easy to

check water level) contains liquid water, disposable/ reusable

Heat source – heated rods immersed in water or plate at bottom of humidification chamber

Inspiratory tube – conveys humidified gas from humidifier outlet to patient

If unheated gas will cool and lose some of its moisture as it travels to the patient, water trap necessary to collect condensed water

Heated or insulated more precise control of temperature and humidity delivered to patient, avoids moisture rainout

Temperature monitor – to measure gas to measure gas temperature at patient end of breathing systemtemperature at patient end of breathing system

Thermostat device 1.1.Servo-controlled unitsServo-controlled units – automatically regulates – automatically regulates

power to heating element in response to power to heating element in response to temperature sensed by a probe near patient temperature sensed by a probe near patient connection/ humidifier outlet, these device connection/ humidifier outlet, these device equipped with alarmequipped with alarm

2.2.Nonservo-controlled units Nonservo-controlled units – provides power to – provides power to heating element according to setting of a control, heating element according to setting of a control, irrespective of delivered temperatureirrespective of delivered temperature

Controls – most humidifier allow temperature most humidifier allow temperature selection at end of delivery tube or at selection at end of delivery tube or at humidification chamber outlethumidification chamber outlet

AlarmsAlarms alarm may warn when temp. at patient alarm may warn when temp. at patient end of the circuit deviates from set temp , when end of the circuit deviates from set temp , when displacement of temperature probe, disconnection displacement of temperature probe, disconnection of heater wire, low water level in humidification of heater wire, low water level in humidification chamber, faulty airway temperature probe , lack of chamber, faulty airway temperature probe , lack of gas flow in the circuitgas flow in the circuit

In circle system, heated humidifier is placed in the inspiratory limb downstream of unidirectional valve by using an accessory breathing tube

Must not be placed in the expiratory limb Filter, if used, must be placed upstream of

humidifier to prevent it from becoming clogged

In Mapleson systems, humidifier is usually placed in fresh gas supply tube

Humidifier must be lower than patient to avoid risk of water running down the tubing into the patient

Condensate must be drained periodically & a water trap inserted in the most dependent part of the tubing to prevent blockage or aspiration

Heater wire in delivery tube should not be bunched, but strung evenly along length of tube

Delivery tube should not rest on other surfaces or be covered with sheets, blankets, or other materials; a boom arm or tube tree may be used for support

AdvantagesAdvantages – –

1.Capable of delivering saturated gas at body temperature or above, even with high flow rates

2.More effective humidification than an HME

Disadvantages Disadvantages – –

1.Bulky and somewhat complex

2.Involve high maintenance costs, electrical hazards, and increased work (temperature control, refilling the reservoir, draining condensate, cleaning, and sterilization)

3.Offers relatively little protection against heat loss during anesthesia as compared to circulating water and forced-air warming

Assessment of needEither an HME or an HH can be used to

condition inspired gases:HMEs are better suited for short-term use (≤96

hours) and during transport.HHs should be used for patients requiring long-

term mechanical ventilation (>96 hours) or for patients for whom HME use is contraindicated.

Nebulizer Produces and disperses liquid particles in a gas

stream or aerosol mistUse - produce humidification & deliver drug

such as bronchodilator, mucolytic agent and decongestant

Size of the water droplet is between 0.5 to 5µmParticles more than 5µm unable to reach the

peripheral airwaysParticles less 0.5µm is very light, and will come

back with expired gases without being deposited in airways

2 types of nebulizer pneumatic Nebulizers Ultrasonic nebulizers.

pneumatic nebulizers Works: by forced a jet of

high-pressure gas into a liquid - inducing shearing forces - breaking the water up into fine water particles

produces particles of size 5 to 30 µm

only 30 to 40% of particles produced are in optimal range

Most of the particles get deposited in wall of main airways

Ultrasonic nebulizer used piezoeeletric crystal Works: Crystal transducer converts:

radio waves into high-frequency mechanical vibrations

vibration is transmitted to the water surface

The high mechanical energy creates cavitation in the fluid

it formed a standing wave which will disperses liquid particles

Frequency of oscillation determines the size of the water particles

Aerosol size of 1 to 10 µm 95% of particles produced are in optimal

range Particles deposited directly in airway Very effective for deliver bronchodilator

Hazards from nebulizer:cause over hydrationsHypothermiaInfection can be transmittededema of the airway wall

Advantages and disadvantages of nebulizer

AdvantagesIt can carry air that fully saturated with water vapor without heat.We can increase the amount of the water vapor in the inhaled air. Disadvantage

The pneumatic nebulizer needs high air flow to operate. The ultrasonic nebulizer need electric supply to operate thus it may cause electric shock

SCAVENGING SYSTEM

INTRODUCTION : scavenging is the collection and subsequent

removal of waste anesthetic gases from both the anesthesia machine and the anesthetising location.

Trace level of an anesthetic gas is a conc. far below that needed for clinical anesthesia or can be detected by smell

Trace gases conc. depending on FGF, ventilation system , the length of time of anesthesia, anesthetic technique and other variables

Trace gas level expressed in parts per million (ppm)

Problems attributed to trace gases Spontaneous abortions : Higher rates of spontaneous abortion in OR

personnel than in women in other settings.

Infertility : Studies found higher than expected rates of involuntary infertility among exposed

Impaired Skilled performance : one study showed that neuropsychological symptoms and tiredness were reported more by individuals in OR that are less scavenged

Birth Defects : Studies in human found increase in congenital abnormalities in children of exposed personnel

Carcinogenicity : A large study found higher risk of cancer in females than males who are exposed, but data has been questioned.

Liver disease : recurrent hepatitis – halothane reported in few individuals

Renal Disease Hematological : higher rate of leukamia.Cardiac Disease : higher Freq of HTN and

dysrrthythmias

In 1977 National Institute

for Occupational Safety and Health (NIOSH) –

recommended exposure limits for trace gas level (nitrous oxide and halogenated agent )

anesthetic gas

Max. TWA conc.[ppm]

Halogenated agent alone

2

Nitrous oxide alone

25

Halogenated gas +nitrous oxide

0.5 + 25

Dental facilities[nitrous oxide alone]

50

The 2 major causes of waste gas contamination in the O.R :

Equipment failure or lack of understanding of proper equipment

The anesthetic technique used - Failure to turn off gas flow control valve and

vaporizers when the circuit is disconnected from the patient.

use poorly fitting masks. Flushing of circuit in room. Using uncuffed endotracheal tubes that do

not create a completely sealed airway or using cuffed tubes without inflating the cuff

Spilling liquid anesthetic during the filling of

vaporizers.

Use of breathing circuits other than circle system

The use of scavenging devices with anesthesia delivery systems is the most effective way to decrease waste anesthetic gases.

An efficient scavenging system is capable of reducing ambient concentrations of waste gases by up to 90%.

Components of the scavenger system:Gas collection assembly.Transfer tubing.Scavenging interface .Gas disposal tubing .Gas disposal assembly.

1.Gas collecting assemblyCaptures excess anesthetic gases and delivers

it to the transfer tubing.

WAG are vented from anesthesia system through either adjustable pressure limiting valve or ventilator relief valve.

Conventional machine have seprate outlet port for these valve however newer have only one

some anesthetic workstations may also exhaust the ventilator drive gas in to scavenging system

2.Transfer tubingThe transfer tubes carries excess gas from gas collecting

assembly to scavenging interface.

The tubes must have 30 mm connectors on either end, sometimes yellow color-coded .

The tubes should be sufficiently rigid to prevent kinking and as short as possible to minimize the chance of occlusion.

Separate tubes from the APL valve and ventilator relief valve merge into a single hose before they enter scavenging interface.

If the transfer tube is occluded, baseline breathing circuit pressure will increase and barotrauma can occur.

3.Scavenging interface The scavenger interface is the most important

component because it protects the breathing circuit or ventilator from excess positive or negative pressure.

the interface should limit pressure between -.5 and 3.5 cm of h2o under normal working condition.

Positive-pressure relief is mandatory, irrespective of the type of disposable system (active or passive) used, to vent excess gas in case of occlusion distal to interface.

negative pressure relief will be necessary in active disposable system to protect breathing circuit or ventilator from subatmospheric pressure .

scavenger interfaces may be open closed

OPEN INTERFACE:It contains no valves and is

open to the atmosphere, allowing positive and negative pressure relief.

Open interfaces should be used only with active disposable systems that have a central evacuation system.

open interfaces require a reservoir because waste gases are intermittently discharged in surges whereas flow from the evacuation system is continuous.

The efficiency of it depends on several factors:

A.The vacuum flow rate per min must equal or exceed the minute volume of excess gases to prevent spillage.

B.Spillage will occur if the volume of a single exhaled breath exceeds the capacity of reservoir. Open interfaces are safer for the patients.

CLOSED INTERFACE:

It communicates with the atmosphere through valves.

Two types of closed interfaces are commercially available:

positive pressure relief only positive and negative pressure relief

POSITIVE PRESSURE RELIEF ONLY:

It has a single positive pressure relief valve and is designated to be used only with passive disposable systems.

Transfer of the waste gas from the interface to the disposable system relies on the slight positive pressure of the waste gases leaving the patient’s breathing system, because a negative pressure evacuation system is not used.

In this system reservoir bag is not required.

POSITIVE AND NEGATIVE PRESSURE RELIEF:

It has positive and negative pressure relief valve in addition to a reservoir bag.

It is used with active disposable systems.The effectiveness of a closed system in preventing spillage

depends on: the rate of waste gas inflow the evacuation flow rate the size of the reservoirLeakage occurs only when the reservoir bag becomes fully

inflated and pressure increases sufficiently to open the positive pressure relief valve .

4.Gas disposal tubingThe gas disposable tubing conducts waste gas

from the Scavenging interface to the gas disposable assembly.

It should be collapse proof and should run overhead, if possible to minimize the chance of accidental occlusion.

Connection to an active gas disposable system should be DISS type connector

5.Gas disposal assemblyIt ultimately eliminates excess waste gas.It is of two types:

Active Passive

Active assembly: most commonly used. It uses central evacuation

system.A vacuum pump serves as mechanical flow inducing

device that removes the waste gases.An interface with a negative pressure relief valve is

mandatory because the pressure within the system is negative.

Central evacuations are - Piped Vacuum - central vaccum system - Active duct system - employs flow inducing

devices (fans , pumps , blowers etc..) to move large volume of gas at low pressures

Advantages Convenient in large hospitals, where many

machines are in use in different locationsMore effective at keeping pollution low level

because most leaks will be inwardDisadvantages  Vacuum system and pipe work is a major

expense  not a automatic must be turn ON and OFF

Passive disposable system: does not use a mechanical flow inducing device. anesthetic gases flow through the system by the

pressure raised above atmospheric by the patient exhaling, by manually squeezing the reservoir beg , or by ventilator

Positive pressure relief is mandatory, but a negative pressure relief and reservoir are not.

types - Room ventilation system - Recirculating or nonrecirculating - Piping direct to atmosphere - Adsorption devices - Catalyst decomposition

use activated charcoal or zeolite

connected to the outlet of the scavenging system

removes halogenated anesthetics but not nitrous oxide

These are simple and portable Halogenated gases not

release to atmosphere (decrease green house effect)

Adsorption device

DisadvantagesThey are fairly expensive and are effective for short period of time  replaced regularly and pose to storage and disposal problem  Does not remove nitrous oxid

Catalytic Decomposition : Catalytic decomposition can be used to

convert nitrous oxide to nitrogen and oxygen, reducing its contribution to the greenhouse effect

Evaluation of Anesthetic Equipment

Each piece of equipment involved in the delivery of inhalant anesthetics should be evaluated regularly to assure its function and integrity.

Procedures for checkout of anesthesia equipment, depending on the equipment to be used, should include the following: Status of the high-pressure system, including the oxygen supply and nitrous oxide supply - The nitrous oxide supply should not leak when the cylinder valve is on and the nitrous oxide flowmeter is off.

Status of the low-pressure system (flowmeter function) - A negative-pressure leak test should be performed at the common gas outlet or the outlet of the vaporizer immediately upstream from the breathing system.

Status of the breathing system - An appropriate leak test for a circle system and Noncircle systems should be done. The quantity of leakage can be measured by determining the flow rate of oxygen necessary to maintain a constant pressure in the system, and the leak rate should be less than 300 ml/min at 30 cm of h2O.

Status of the scavenging system - The scavenging system should be properly attached at all connectors, and the appropriate vacuum should be assured for active systems. If charcoal canisters are employed for scavenging, they should be changed at appropriate intervals.

Monitoring of the Effectiveness of Antipollution Techniques

Monitoring trace-gas concentrations in the workplace provides a quantitative assessment of the effectiveness of a waste-gas control program.

An air-monitoring program is most appropriately started after anesthesia delivery systems have been equipped with scavenging systems and after other techniques for minimizing waste gas pollution are in place.

An ideal approach would include frequent air monitoring, at least semiannual evaluations.

Equipment for determining trace gas conc. infrared analyzer , dosimeter . Ionizing leak detector

Effectiveness Unscavenged operating rooms show 10-70

ppm halothane, and 400-3000 ppm N2O.

scavenging brings these levels down to 1 and 60 ppm respectively.

Adding careful attention to leaks and technique can yield levels as low as 0.005 and 1 ppm.

HAZARDS Scavenging system functionally extends the anesthesia circuit

all the way from the anesthesia machine to the disposable site.

Obstruction of scavenging pathway can cause excessive positive pressure in the breathing circuit and barotrauma can occur.

excessive vacuum applied can result in undesirable negative pressures within breathing system.

Loss of Monitoring Input – it may mask the strong odor of a volatile anesthetic agent, delaying recognition of an overdose

Alarm failure – neg. pressure from the scavenging system interface prevent the bellows from collapsing when breathing system is disconnected & Low airway pressure alarm not activated.

THANK THANK U….U….