Patient Ventilator Circuit Flashcards
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
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Inspiratory Filters
- Located where the inspiratory limb leaves the ventilator
- Eliminates bacteria from the driving gas
- Prevents retrograde contamination of the machine
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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
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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
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
Simple
Portable
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
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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
Optimal:
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
- Minimize Circuit Changes
- Use in-line suction
- Active Humidity
- Minimize Cross contamination
- Keep uneccessary Equitment out of room
- 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
