Humidity Therapy and Humidifiers

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Humidity Therapy and Humidifiers

• RET 2274
• Respiratory Care Theory 1
• Module 5.0

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Humidity Therapy and Humidifiers

• Humidity
• Water that exists as individual molecules in the
  vaporous or gaseous state and is present in the
  air we breathe often described as water vapor

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Humidity Therapy and Humidifiers

• Humidity Therapy
• Involves adding water vapor and (sometimes) heat
  to an inspired gas
• Primary goal of humidification is to maintain
  normal physiological conditions in the lower
  airways or treat abnormal conditions

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Humidity Therapy and Humidifiers

• Humidity Therapy
• Administration of dry medical gases at flows
  greater than 4 L/min to the upper airway causes
  immediate heat and water loss, and if prolonged,
  causes structural damage

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Humidity Therapy and Humidifiers

• Absolute Humidity
• Is the actual content or weight of water present
  in a given volume of gas
• Expressed as
• Grams per cubic meter (g/m3)
• Milligrams per liter (mg/L)
• Also know as water content

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Humidity Therapy and Humidifiers

• Relative Humidity (RH)
• Is the ratio of actual content or weight or the
  water present in a gas relative to the samples
  capacity to hold water at that temperature
• Expressed as a percentage
• RH measured humidity (content) X 100
• water capacity
• When the amount of water that a gas contains at a
  given temperature is equal to the gass capacity,
  the RH is 100 - described as saturated

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Humidity Therapy and Humidifiers

• Relative Humidity (RH)
• Increasing the temperature of a gas, increases
  its capacity to hold water
• If absolute humidity is held constant, increasing
  the temperature of the gas will decrease the RH
• If absolute humidity is held constant, decreasing
  the temperature of the gas will increase the RH
  or it will remain at 100

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Humidity Therapy and Humidifiers

• Relative Humidity (RH)
• ?Temp ?RH
• ?Temp ?RH

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Humidity Therapy and Humidifiers

• Condensation
• Cooling a gas that has an RH of 100 decreases
  its capacity to hold water, which results in
  water being squeezed out of the gas
• ?Temp ?RH

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Condensation
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Humidity Therapy and Humidifiers

• Evaporation
• The process of water moving from a liquid to a
  gaseous state at temperatures lower than its
  boiling point
• The warmer the air contacting the water surface,
  the faster the rate of evaporation
• Heating water will increase the rate of
  evaporation

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Humidity Therapy and Humidifiers

• Humidity
• Partial Pressure
• The random motion of water molecules exerts a
  pressure (water vapor pressure) in a way similar
  to gas exerting pressure
• As the temperature of a gas increases, kinetic
  activity increases, so the pressure also
  increases

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Humidity Therapy and Humidifiers

• Humidity
• Partial Pressure
• Its magnitude is solely dependent upon
  temperature and relative humidity not upon
  barometric pressure
• The partial pressure of water vapor must always
  be accounted for (subtracted) when calculating
  the partial pressure of other gases in a mixture

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Humidity Therapy and Humidifiers

• Humidity
• Partial Pressure
• Alveolar Air Equation
• FiO2 (PB Water Vapor Pressure) PaCO2
• 0.8
• .40 (760mm Hg 47 mm Hg) 40 mm Hg
• 0.8

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Humidity Therapy and Humidifiers

• Physiological Control of Heat and Moisture
  Exchange
• Primary function of the upper respiratory tract
• Nose (primary)
• Heats and humidifies gas on inspiration and cools
  and reclaims water from the gas that is exhaled
• Sinuses, Trachea, and Bronchi
• Also aid in heating and humidifying the inspired
  gases

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Humidity Therapy and Humidifiers

• Physiological Control of Heat Moisture Exchange
• As inspired gas moves into the lungs, it achieves
  BTPS (body temperature, 37? C barometric
  pressure saturated with water vapor 100
  relative humidity at 37? C)
• Isothermic Saturation Boundary (ISB)
• The point in the respiratory tract at which
  incoming gas reaches BTPS
• Below the ISB, temperature and relative humidity
  remain the same

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Humidity Therapy and Humidifiers

• Indications for Humidification
• Primary goal of humidification is to maintain
  normal physiological conditions in the lower
  airways or treat abnormal conditions

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Humidity Therapy and Humidifiers

• Indications for Humidification
• Administration of dry medical gases at flows
  greater than 4 L/min to the upper airway causes
  immediate heat and water loss, and if prolonged,
  causes structural damage
• Ciliary motility is reduced
• Airways become irritable
• Mucous production increases
• Pulmonary secretions become thick and inspissated

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Humidity Therapy and Humidifiers

• Indications for Humidification
• Prolonged breathing of improperly conditioned
  gases through a tracheal airway can result in the
  following
• Hypothermia
• Inspissation of airway secretions
• Mucociliary dysfunction
• Destruction of airway epithelium
• Atelectasis
• As long as inspired humidity is at least 60 of
  BTPS conditions, no injury occurs in normal lungs

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Humidity Therapy and Humidifiers

• Indications for Humidification
• Humidified gas delivered to an artificial airway
  (endotracheal or tracheostomy tube) must be
  between 31? and 35? C with a minimum of 30 mg/L
  of absolute humidity
• To maintain the appropriate temperature and
  humidity levels, monitoring at the interface of
  the patient and humidifying device is necessary

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Humidity Therapy and Humidifiers

• Equipment
• Humidifier is a device that adds molecular water
  to gas

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Humidity Therapy and Humidifiers

• Physical Principles Governing Humidifiers
• Temperature
• The greater the temperature of a gas, the more
  water it can hold
• The cooler the water in a humidifier the less
  efficient they are

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Humidity Therapy and Humidifiers

• Physical Principles Governing Humidifiers
• Surface Area
• The greater the area of contact between water and
  gas, the more opportunity for evaporation to
  occur
• Passover humidifiers pass gas over a large
  surface area of water

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Humidity Therapy and Humidifiers

• Physical Principles Governing Humidifiers
• Surface Area
• Bubble-diffuser type humidifiers

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Humidity Therapy and Humidifiers

• Physical Principles Governing Humidifiers
• Surface Area
• Wick technologies use porous water-absorbent
  materials to increase surface area

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Humidity Therapy and Humidifiers

• Physical Principles Governing Humidifiers
• Contact Time
• The longer gas remains in contact with water, the
  greater the opportunity for evaporation to occur
• Depth of water column (bubble type)
• ? depth of water ? evaporation
• ? depth of water ? evaporation
• Flow rate of gas (passover and wick)
• ? flow rate ? evaporation
• ? flow rate ? evaporation

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Humidity Therapy and Humidifiers

• Types of Humidifiers
• Active
• Actively adds heat and/or water to the
  device/patient interface
• Bubble
• Passover
• Membrane
• Passive
• Recycling exhaled heat and humidity from the
  patient
• HME

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Humidity Therapy and Humidifiers

• Types of Humidifiers
• Bubble Humidifier (Active)
• Breaks an underwater gas stream into small
  bubbles
• Unheated commonly used oronasal O2 delivery
  systems (e.g., cannula)
• Goal to raise the water vapor content of the gas
  to ambient levels
• Can generate aerosols at high flows
• Equipped with pressure-relief valve pop-off

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Humidity Therapy and Humidifiers

• Types of Humidifiers
• Passover Humidifier (Active)
• Directs gas over a water surface
• Two types
• Wick
• Membrane

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Humidity Therapy and Humidifiers

• Types of Humidifiers
• Passover Humidifier
• Wick type
• A cylinder of absorbent material (wick) is placed
  upright in a reservoir of water and surrounded by
  a heating element
• Dry gas enters the chamber, flows around the
  wick, picks up moisture, and leaves the chamber
  saturated with water vapor

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Humidity Therapy and Humidifiers

• Types of Humidifiers
• Passover Humidifier
• Membrane type
• Separates the water from the gas stream by means
  of a hydrophobic membrane
• Water vapor molecules pass through the membrane
  (liquid cannot)
• Dry gas enters the chamber, flows across the
  membrane, picks up moisture, and leaves the
  chamber saturated with water vapor

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Humidity Therapy and Humidifiers

• Types of Humidifiers
• Heat and Moisture Exchangers (HME)
• Passive humidifier
• Functions similar to the upper airway
• Captures exhaled heat and moisture during a
  patients exhalation and returns it to the
  patient during the next inspiration

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Humidity Therapy and Humidifiers

• Types of Humidifiers
• HME (Passive)
• Best Suited for
• Short-term mechanical ventilation ( 96 hours)
• Minute ventilation lt 10 L/min
• Limited secretions
• Normal body temperature

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Humidity Therapy and Humidifiers

• Types of Humidifiers
• HME (Passive)
• Rule of Thumb
• You can estimate if an HME is performing well at
  the bedside by visually confirming condensation
  in the flex tube. Lack of condensate may be a
  clue that humidification is less than adequate
  and that alternative systems may be appropriate
  for use with that particular patient.

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Humidity Therapy and Humidifiers

• Heaters, Reservoirs, and Feed Systems
• Heat improves the water output of bubble and
  passover humidifiers
• Heated humidifiers are used mainly for patients
  with bypassed upper airways and/or for those
  receiving mechanical ventilatory support

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Humidity Therapy and Humidifiers

• Heaters, Reservoir, and Feed Systems

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Humidity Therapy and Humidifiers

• Heaters, Reservoir, and Feed Systems

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Humidity Therapy and Humidifiers

• Heaters, Reservoir, and Feed Systems