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Flashcards in Patient Ventilator Circuit Deck (35):

Must Have Components

  • Inspiratory Limb
  • Humidification
    • HME
    • Humidifiers/ Water Trap(s)
    • +/- Heated Wires
  • Patient Wye
  • Expiratory limb
  • Exhalation valve


Inspiration Limb

Tubing that connect the ventilator to one side of the patient wye

Route for breath delivery (Inspiration)


Expiratory Limb

Tubing that connect the ventilator to the other side of the patient wye

Route for exhaled gases (Expiration)

May connect back to the vent (when an internal expiratory valve) or not (when an external expiratory valve) 


Expiratory Valve

An essential component as without it no flow could be directed to the patient

Located after the inspiratory limb

Can be internal (located inside the ventilator) or external (located outside of the ventilator)

Can be a diaphragm, balloon valve or plunger

Inspiration: The expiratory valve closes allowing flow to be directed into he patient

Expiration: The valve is open to allow the patient to exhale

Newer vents are using active exhalation valves that are low resistance and allow for more mode options


Patient Wye

Connects both inspiratory and expiratory limbs near the patient

Any circuit distal to the wye is added deadspace (=mechanical deadspace)

Therefore the flex tube and connector are deadspace


Bacterial Filters Locations

  • Inspiratory Filters
    • Located where the inspiratory limb leaves the ventilator
    • Eliminates bacteria from the driving gas
    • Prevents retrograde contamination of the machine
  • Expiratory Filters
    • Located where the expiratory limb returns to the vent
    • Protects the ventilator internal components and filters exhaled air before it enters the surroundings
  • Other Filters Used
    • Many HMEs incorporate a bacterial filter (HMEF)

RULE OF THUMB: If your HME has a filter (HMEF) then you do not require any other filters. If using active humidity best practice is to use both and inspiratory and expiratory filter


Bacterial Filters The Numbers

Removes bacteria and particular matter

Removes 0.3 μm particles at 99.97 % efficiency

Bacteria are sized from 0.5–50 μm

Resistance: ~ 4.0 cmH2O at 100 LPM flow


Bacteria Filter-Clinical Use

Will depends upon the vent

Some incorporate both inspiration and expiratory filters (eg. 840)

Others don’t use an expiratory filter as the vent is designed with the replaceable/autoclavable expiratory components that are cleaned between patients

While best practice would dictate an inspiratory filter always be used often it is not. 

The high pressure air/O2 inputs often have a filter to prevent debris from the wall source; however, these won’t prevent debris from inside the vent reaching the patient


Flex Tube/Connector

Piece of circuitry added to the wye for ease of patient connection

Adds mechanical deadspace

Not absolutely necessary but definitely desired


External Nebulizer

A nebulizer T’d into the inspiratory limb to deliver aerosolized medication to the patient

Can be powered by the ventilator or by an external flowmeter- If using an external flowmeter it adds to the delivered tidal volume

Cannot be used if there is a HME inline distally (ie. downstream)-HME needs to be removed during treatment

Rarely used clinically


Inline Suction Catheter

Allows for suctioning without breaking the circuit

Reduces both caregiver and patient risk of exposure to infectious materials

Ability to reuse can reduce costs


MDI Chamber

Specifically designed to be placed in ventilator circuit

Typically placed after wye and before flex tube

Ideally:  the closer to the patient it is placed, the less loss of medication to the circuit components-Note:  this does result in increased deadspace!

Some chambers designed to collapse between use



Humidification must be added to a ventilator circuit as the patient’s upper airway is bypassed


Passive Humidity

Aka a dry circuit

Achieved via a heat moisture exchanger (HME) or HMEF which contains a bacterial/viral filter

A passive humidification device will recycle the exhaled heat and humidity from the pt (does not add heat or water to the system)

Placed distal to the pt. wye

Increased deadspace to the circuit, which is why it is not used in neonatal ventilation 


Active Humidify

Aka a wet circuit

Heated Humidifier

Heated Wires-Most commonly in both the inspiratory and expiratory limb

We chose heated humidity or HME (NOT BOTH)

Considered active humidity as we are actively adding heat and water to the patient gases

Consider contact time, surface area, and temperature.


Goals of Humidification

To provide adequate humidification and hear to the inspired gas to approximate normal inspiratory conditions at the point of entry

Helps to ensure normal operation of the mucociliary tract

Cold, dry air, reduced ciliary mortality, airways become irritable, mucous produce increases and become thick and encrusting


Advantages of HME



Reduced Cost

Eliminates risk of electric shock


Application of HME

Best suited for short term use-AARC says less than 96 hours or for transport, CHR uses on all patients except those requiring heated humidity

Recommended changing: Q48h-Q96h and as needed. The more infrequent changing (relative to Q24h that was recently practiced) has no increased risk of nosocomial infection. CHR: once a week and per as needed

Other than time in use why would you change an HME- Because as they become saturated the resistance of the circuit is increased, therefore oversaturation/resistance/gummed up with secretions


Contrindications of HME

Thick, copious or bloody secretions

Decreased expired VT (< 70% inspired):  seen with cuffless ETT, incompetent cuff on ETT, bronchopleural fistulas

Hypothermic patients (Temp < 32 °C)

Patients with high minute volumes (> 10 Lpm)

During in-line aerosolized treatments

In conjunction with a heated humidifier

In patients with small VT when the HME has a large internal deadspace (ie. Not used in neo’s and with caution in peds)



Hygroscopic Condenser Humidifiers

  • Most commonly used HME
  • Uses a condensing element of low thermal conductivity
    • Ex. Paper foam
  • The material is impregnated with a hydroscopic salt (calcium or lithium chloride)
    • Helps capture extra moisture from exhaled gases
    • Water is absorbed to inhaled gases without cooling
  • Inspired gases ~ 28°C, 27 mg/L
    • At 37 °C = 27/44 = ~ 70% RH!
  • Compared to simple condenser HMEs, the HCH type is more efficient in recycling the humidity


When Must Active Humidity Used

Bloody secretions

Thick, tenacious sputum

Hypothermia (core temp <32 °C)

Burn patients

Patients in which an HME is contraindicated for


Component Required in Heated Humidity

Heated humidifier base with chamber (typically a pass-over)

Temperature Monitoring-Typically done as gas leaves the chamber and at the patient wye

Water Traps-Newer technology circuit materials makes these unnecessary. In older circuits you need a water trap in the expiratory limb always and in the inspiratory limb when there is no heated wire

Expiratory Filter-As active humidity systems are more likely to grow contaminants we filter expired gases before they enter the room…so, vents that didn’t utilize an expiratory filter when an HMEF is used need to add one now!


Active Humidity-Heated Wires

Typically located in both the inspiratory and expiratory limbs

Purpose is to heat the gas further to prevent condensation (aka “rain out”)

Are optional but desirable! (Almost always used though!)

Reduces risk of contamination of circuit

Reduces risk of water entering airway

The heated wire heats the gas to higher than the humidifier pot temperature. To increase the capacity of the gas to hold water thereby preventing rainout.


Heated Wires Configuration 

Possible configurations: No heated wires, Inspiratory limb heated-wire only, Inspiratory and expiratory limb heated-wires


Active Humidity-Water Traps


  • As gas travels from the humidifier to the patient, or from the patient down the expiratory limb, the gas will cool (if no heated wire) and condensation (rain out) will occur, and water trap(s) are needed to collect this “rain-out"
  • The above are the minimum water traps needed---you may see extra water traps used!
  • Water traps should be the lowest point in the circuit so that proper drainage can occur.


Where are Water Traps

No heated wire:  need both an I and E water trap

I heated wire: need an E limb water trap

I and E heated wires:  still need an E limb water trap

I and E heated wires in a new technology circuit:  no water traps required

It is never wrong, and in fact good practice, to always use an E water trap to ensure no rain-out enters the ventilator


Active Humidity-Clinical Uses

Need to ensure that “Sterile water for Inhalation” is used to fill the pots to minimize risk of contaminants as non-sterile water can result in bacterial/viral contamination and VAP

Humidifier pots add to the compressible volume of the circuit

Using an auto-fill chamber will minimize fluctuations in the compressible volume and therefore ensure accuracy of delivered volumes to the patient

Auto-fill chambers also have the benefit of delivering a more consistent temperature


The New Technology Active Humidity Circuits

These disposable circuits are specially designed to eliminate the need for water traps as rain-out is effectively eliminated

  • Special Features: 
    • Dual limb heated wire-Inspiratory limb uses a “spiral heated wire” for more even heating effectively eliminating rain-out
    • Expiratory limb made of material that is permeable to water vapour
      • Water vapour evaporates through this and gas reaching ventilator is much reduced in absolute humidity
      • Designed to not be permeable to bacteria/viruses

Paradoxically, using water traps in these new circuits can actually cause the rainout, as the water traps are not heated the cool surface actually encourages condensation


Heated Humidity:  Function of the Typical System

These are servo-controlled using a negative feedback system


Heated Humidity:  What Temperature

The key factor in determining the capacity of a gas to hold water

In a spontaneously breathing patient inhaled gases are at 100% RH and 37 °C by the time they reach the carina


37 °C with 100% RH and 44 mg/L when it reaches the patient a/w!


Humidication- Minimizing Contamination 

Ventilator circuits and their condensate have been implicated for decades in the development of VAP (ventilator-associated pneumonia)

VAP is very costly!  It increases mortality and morbidity of the patients as well as costs the health care system millions/billions of dollars a year.

Recent data shows that VAP is primarily associated with silent aspiration of oral secretions and gastric contents

Ventilator circuits and condensate are typically contaminated within hours, however, this should only be from the patient’s airway, if appropriate precautions were taken


How to Minimize Circuit Contamination 

  1. Minimize Circuit Changes
  2. Use in-line suction
  3. Active Humidity
  4. Minimize Cross contamination 
  5. Keep uneccessary Equitment out of room 
  6. Be vigilant in your practice


Minimize Circuit Changes

Current recommendation is no more than Q7d

Avoid breaking the circuit unless absolutely necessary


When to change an inline suction catheter

Only when the circuit is changes or equitment malfuntcion 


When to change a Yankeuer

Change patient’s Yankeur suction/cover and tubing Q24h and prn