1. HUMIDIFIERS, NEBULIZERS
(ATOMIZERS) AND MUCOLYTICS IN
ANAESTHESIA AND CRITICAL CARE
Dr.Avneesh Khare
Resident Doctor
Department of Anaesthesiology
SMS Medical College & Hospitals
Jaipur
Moderator:
Dr.P.S.Lamba
Associate Professor
Department of Anaesthesiology
SMS Medical College & Hospitals
Jaipur

2. HUMIDIFICATION
INTRODUCTION
• 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

3. HUMIDIFICATION
INTRODUCTION (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

4. HUMIDIFICATION
INTRODUCTION (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

5. 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

6. 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

7. SOURCES OF HUMIDITY (contd.)
• Humidifiers –
a. Passive (Heat and Moisture
Exchangers/ HMEs) – hydrophobic/
hygroscopic
b. Active – unheated/ heated
• Nebulisers

8. 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

9. 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

13. PASSIVE HUMIDIFIERS (contd.)
• Most modern HMEs are of 2 types:
a. Hydrophobic
b. Hygroscopic

14. 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

15. 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

16. PASSIVE HUMIDIFIERS (contd.)
Type Hygroscopic Hydrophobic
Heat and moisture Excellent Good
exchanging efficiency
Effect of increased tidal Slight decrease Significant decrease
volume on heat and
moisture exchange
Filtration efficiency Good Excellent
when dry
Filtration efficiency Poor Excellent
when wet
Resistance when dry Low Low
Resistance when wet Significantly Slightly increased
increased
Effect of nebulised Greatly increased Little effect
medications resistance

17. 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

18. 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

19. 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

21. PASSIVE HUMIDIFIERS (contd.)
• Advantages –
1. Inexpensive
2. Easy to use
3. 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

22. 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

23. 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. Unheated
2. Heated

24. 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

26. 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

27. 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

28. 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

29. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. 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

40. NEBULIZERS (contd.)
• Most commonly used are of 2 types –
1. Pneumatically driven (gas-driven, jet,
high pressure, compressed gas)
2. Ultrasonic

41. 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

44. 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

46. 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

47. 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

48. 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

49. 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

50. MUCOLYTICS (contd.)
• N-acetylcysteine (NAC)
• Mesna
• Sodium bicarbonate
• Dornase alpha (Pulmozyme)
• Others – ambroxol, bromhexine,
carbocisteine, domiodol, eprazinone,
erdosteine, letosteine, neltenexine,
sobrerol, stepronin, tiopronin

51. 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)

52. 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

53. NAC (contd.)

54. 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

55. 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.

56. 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

57. 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)

58. 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

59. PULMOZYME (contd.)

60. 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

61. THANKS