HUMIDIFIERS, NEBULIZERS (ATOMIZERS) AND MUCOLYTICS IN ANAESTHESIA AND CRITICAL CAREDr.Avneesh KhareResident DoctorDepartment of AnaesthesiologySMS Medical College & HospitalsJaipur Moderator: Dr.P.S.Lamba Associate Professor Department of Anaesthesiology SMS Medical College & Hospitals Jaipur

HUMIDIFICATIONINTRODUCTION

• HUMIDITY – general term used to describe amount of water vapor in gas / air

• Water is intentionally removed from medical gases so that gases delivered from anaesthesia machine are dry and at room temperature

• Gases must therefore be warmed to body temperature and saturated with water by upper respiratory tract

• Tracheal intubation and high fresh gas flows bypass this normal humidification by upper airways and expose lower airways to dry (< 10 mg H2O/L), room temperature gases

HUMIDIFICATIONINTRODUCTION (contd.)

• Prolonged humidification of gases by lower respiratory tract leads to dehydration of mucosa, altered ciliary function, impairment of surfactant activity, loss of body heat (heat of vaporization for water)

• If excessively prolonged, it could potentially lead to inspissation of secretions, airway/ tracheal tube obstruction, atelectasis, and even ventilation/ perfusion mismatching particularly in patients with underlying lung disease

HUMIDIFICATIONINTRODUCTION (contd.)

• Artificial humidification is of greatest benefit in pediatric patients, patients at increased risk for developing pulmonary complications, older patients with severe underlying lung pathology e.g. cystic fibrosis, and long procedures

• Excessive humidity (increased water load) may cause ciliary degeneration and paralysis, pulmonary edema, altered alveolar - arterial O2 gradient, decreased vital capacity and compliance, and decrease in hematocrit and serum sodium

SOURCES OF HUMIDITY• CO2 absorbent – reaction of CO2 with

absorbent releases water

• Exhaled gases – rebreathing in tracheal tube, supraglottic airway device, and connections to breathing system

-almost half of humidity in expired gases is preserved in this manner

• Moistening (Rinsing) breathing tubes and reservoir bag before use

SOURCES OF HUMIDITY (contd.)

• Low fresh gas flows – conserve moisture

• Coaxial breathing circuits – increase humidity more quickly than a system with 2 separate limbs, when combined with low flows

-not very efficient, Bain system (coaxial version of Mapleson D) does not meet optimal humidification requirements because of high fresh gas flow required

SOURCES OF HUMIDITY (contd.)

• Humidifiers – a. Passive (Heat and Moisture Exchangers/ HMEs) – hydrophobic/ hygroscopic b. Active – unheated/ heated

• Nebulisers

PASSIVE HUMIDIFIERS• Simplest 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 Heat and Moisture Exchanging Filter (HMEF) – particularly important when ventilating patients with respiratory infections or compromised immune system

PASSIVE HUMIDIFIERS (contd.)• 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

PASSIVE HUMIDIFIERS (contd.)

• Most modern HMEs are of 2 types:

a. Hydrophobic

b. Hygroscopic

PASSIVE HUMIDIFIERS (contd.)• Hydrophobic HMEs –1. Hydrophobic membrane with small pores,

pleated to increase surface area

2. Allow passage of water vapor but not liquid water at usual ventilatory pressures

3. Efficient bacterial and viral filters

4. Performance may be impaired by high ambient temperatures

PASSIVE HUMIDIFIERS (contd.)• Hygroscopic HMEs – 1. Wool, foam or paper like material coated with

moisture-retaining chemicals

2. Medium may be impregnated with a bactericide

3. Composite hygroscopic HMEs = hygroscopic layer + layer of thin, nonwoven fiber membrane subjected to electric field to increase polarity (improves filtration efficiency and hydrophobicity) more efficient at moisture and temperature conservation than hydrophobic HMEs

PASSIVE HUMIDIFIERS (contd.)Type Hygroscopic Hydrophobic

Heat and moisture exchanging efficiency

Excellent Good

Effect of increased tidal volume on heat and moisture exchange

Slight decrease Significant decrease

Filtration efficiency when dry

Good Excellent

Filtration efficiency when wet

Poor Excellent

Resistance when dry Low Low

Resistance when wet Significantly increased

Slightly increased

Effect of nebulised medications

Greatly increased resistance

Little effect

PASSIVE HUMIDIFIERS (contd.)• Indications - 1. To increase inspired heat and humidity during

both short and long term ventilation

2. Especially useful when transporting intubated patients - transport ventilators frequently have no means for humidifying inspired gases

3. To supply supplemental oxygen to intubated patient/ patient with a supraglottic airway - by connecting oxygen tubing to gas sampling port

PASSIVE HUMIDIFIERS (contd.)• Should be of appropriate size for patient’s

tidal volume

• Connecting more than one in series will improve performance but care should be taken that increase in dead space is not excessive for particular patient (especially small patient)

• Should be visible and accessible at all times in order to detect contamination or disconnection

PASSIVE HUMIDIFIERS (contd.)• May be used for tracheostomised patients

• May be combined with another source like unheated humidifier, but should not be used with heated humidifier

• Nebuliser or metered dose inhaler if used, should be inserted between HME and patient, or HME removed from circuit during aerosol treatment

• Should be replaced if contaminated with secretions

PASSIVE HUMIDIFIERS (contd.)• Advantages – 1. Inexpensive 2. Easy to use3. Small, lightweight, simple in design 4. Silent in operation 5. Do not require water/ external energy

source/ temperature monitor/ alarms 6. No danger of overhydration/

hyperthermia/ burns/ electrical shock

PASSIVE HUMIDIFIERS (contd.)• Disadvantages – 1. Can deliver only limited humidity 2. Insignificant contribution to temperature

preservation 3. Less effective than active humidifiers,

specially after intubation lasting for several days

4. Increased dead space may necessitate increase in tidal volume increased work of breathing

ACTIVE HUMIDIFIERS• Add 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 (vapor-phase humidifier)

• Unlike passive humidifiers, they do not filter respiratory gases

• 2 types – 1. Unheated2. Heated

UNHEATED HUMIDIFIERS • Disposable, 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

• Humidification chamber – contains liquid water, disposable/ reusable, clear (easy to check water level)

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

HEATED HUMIDIFIERS (contd.)• Temperature monitor – to measure gas

temperature at patient end of breathing system

• Thermostat – 1. Servo-controlled units – automatically

regulates power to heating element in response to temperature sensed by a probe near patient connection/ humidifier outlet

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

HEATED HUMIDIFIERS (contd.)• 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

HEATED HUMIDIFIERS (contd.)• Controls – most allow temperature selection at end

of delivery tube or at humidification chamber outlet

• Alarms – to indicate temperature deviation by a fixed amount, displacement of temperature probe, disconnection of heater wire, low water level in humidification chamber, faulty airway temperature probe , lack of gas flow in the circuit

• Standard requirements - An international and a U.S. standard on humidifiers have been published

HEATED HUMIDIFIERS (contd.)

• 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

HEATED HUMIDIFIERS (contd.)• Humidifier must be lower than patient to avoid risk

of water running down the tubing into the patient

• Condensate must be drained periodically or 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

HEATED HUMIDIFIERS (contd.)

• Advantages –

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

2. More effective humidification than an HME

HEATED HUMIDIFIERS (contd.)• 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

NEBULIZERS• Aerosol generators/ atomizers/ nebulizing

humidifiers

• Emit water in the form of an aerosol mist (water vapor plus particulate water)

• Used for producing humdification and delivery of drug directly into respiratory tract

• Drugs delivered by nebulizers – Bronchodilators, decongestants, mucolytic agents, steroids

NEBULIZERS (contd.)• Optimal particle size of droplet (aerosol)

= 0.5 to 5 µm

Particles > 5 µm – unable to reach peripheral airways, deposited in main airways

Particles < 0.5 µm - very light, come back with expired gases without being deposited in airways

NEBULIZERS (contd.)

• Most commonly used are of 2 types – 1. Pneumatically driven (gas-driven, jet,

high pressure, compressed gas)

2. Ultrasonic

NEBULIZERS (contd.)• Pneumatically driven nebulizer works by

pushing a jet of high-pressure gas into a liquid, inducing shearing forces and breaking the water up into fine particles

Should be placed in the fresh gas line (high flow of gas must be used with pneumatic nebulizer)

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

NEBULIZERS (contd.)• Ultrasonic nebulizer produces a fine mist

by subjecting the liquid to a high-frequency, electrically driven resonator

Can be used in the fresh gas line or the

inspiratory limb (No need for a driving gas) Frequency of oscillation determines the size

of the droplets

Creates a denser mist than pneumatic ones

NEBULIZERS (contd.)

Ultrasonic nebulizer produces mist with aerosol size of 1 to 10 µm (95% of particles produced are in optimal range) particles get deposited directly in airways, so very useful for delivery of

bronchodilators directly in peripheral airways

Can nebulize 6 mL of water or drug in 1 minute

NEBULIZERS (contd.)• Hazards – 1. Nebulized drugs may obstruct an HME or filter in the

breathing system

2. Overhydration

3. Hypothermia

4. Transmission of infection

5. Case reports where a nebulizer was connected directly to a tracheal tube without provision for exhalation resulted in pneumothorax in one case

NEBULIZERS (contd.)• Advantage - can deliver gases saturated with water without

heat and, if desired, can produce gases carrying more water

• Disadvantages –1. Somewhat costly

2. Pneumatic nebulizers require high gas flows

3. Ultrasonic nebulizers require a source of electricity and may present electrical hazards

4. May be considerable water deposition in the tubings, requiring frequent draining, water traps in both the inspiratory and exhalation tubes, and posing the dangers of water draining into the patient or blocking the tubing  

MUCOLYTICS• Agents capable of dissolving, digesting or

liquefying mucus (reducing viscosity)

• Classified under ‘mucokinetics’ - a class of drugs which aid in the clearance of mucus from the airways, lungs, bronchi, and trachea

• Useful in patients in the intensive care unit (ICU) with compromised lung function who often have excessive pulmonary secretions and have difficulty clearing mucus

MUCOLYTICS (contd.)

• N-acetylcysteine (NAC)• Mesna• Sodium bicarbonate• Dornase alpha (Pulmozyme)

• Others – ambroxol, bromhexine, carbocisteine, domiodol, eprazinone, erdosteine, letosteine, neltenexine, sobrerol, stepronin, tiopronin

MUCOLYTICS (contd.)• Alter consistency of gel layer of mucus

• Act by – 1. Weakening of intermolecular forces binding

adjacent glycoprotein chains– Disruption of Disulfide Bonds (NAC, Mesna)

2. Alteration of pH to weaken sugar side chains of glycoproteins (Soda bicarb.)

3. Destruction of protein (Proteolysis) contained in the glycoprotein core– Breaking down of DNA in mucus (Dornase alpha)

N-acetylcysteine (NAC)

• Sulfhydryl - containing tripeptide

• Better known as the antidote for acetaminophen overdose

• Primarily a mucolytic agent that acts by disrupting the disulfide bridges between mucoprotein strands in sputum

NAC (contd.)

NAC (contd.)• Available in a liquid preparation (10 or 20% solution)

that can be given as an aerosol spray, or injected directly into the airways

• Aerosolized NAC should be avoided when possible because it is irritating to the airways and can provoke coughing and bronchospasm (particularly in asthmatics)

• Direct instillation of NAC into the tracheal tube is preferred, especially when there is an obstruction

• Daily use of NAC is not advised because the drug solution is hypertonic (even with the saline additive) and can provoke bronchorrhea

NAC (contd.)• Should not be mixed with antibiotics in

the same nebulizer (incompatible)

• Nausea & Vomiting– Disagreeable odor (smells like rotten eggs)

due to the hydrogen sulfide.

• Open vials should be used within 96 hours to prevent contamination.

MESNA

• Organosulfur compound

• MESNA is an acronym for 2-Mercaptoethane sulfonate Na (Na being the symbol for sodium)

• Used in cancer chemotherapy involving cyclophosphamide and ifosamide, as an adjuvant

• As a mucolytic – works in the same way as NAC

SODIUM BICARBONATE• Weak base

• Increasing the pH of mucus weakens the polysaccharide chains

• 2% NaHCO3 solutions are used

• Can be injected directly into the trachea or aerosolized (2-5 mL)

DORNASE ALPHA (PULMOZYME)• Highly purified solution of recombinant

human deoxyribonuclease I (rhDNase), an enzyme which selectively cleaves DNA

• Produced in Chinese hamster ovary cells

• Hydrolyzes the DNA present in sputum/ mucus of cystic fibrosis patients and reduces viscosity in the lungs, promoting improved clearance of secretions

PULMOZYME (contd.)

REFERENCES• Understanding Anaesthesia Equipment (5th Edition)

- Dorsch and Dorsch

• Clinical Anaesthesiology (4th Edition) – Morgan

• Short Textbook Of Anaesthesia (4th Edition) - Ajay Yadav

• The ICU Book (3rd Edition) – Paul Marino

• Various Internet Sites

THANKS