Patient Ventilator Circuit

Question 1

Must Have Components

Answer 1

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

Question 2

Inspiration Limb

Answer 2

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

Route for breath delivery (Inspiration)

Question 3

Expiratory Limb

Answer 3

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)

Question 4

Expiratory Valve

Answer 4

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

Question 5

Patient Wye

Answer 5

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

Question 6

Bacterial Filters Locations

Answer 6

• 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

Question 7

Bacterial Filters The Numbers

Answer 7

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

Question 8

Bacteria Filter-Clinical Use

Answer 8

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

Question 9

Flex Tube/Connector

Answer 9

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

Adds mechanical deadspace

Not absolutely necessary but definitely desired

Question 10

External Nebulizer

Answer 10

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

Question 11

Inline Suction Catheter

Answer 11

Allows for suctioning without breaking the circuit

Reduces both caregiver and patient risk of exposure to infectious materials

Ability to reuse can reduce costs

Question 12

MDI Chamber

Answer 12

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

Question 13

Humidification

Answer 13

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

Question 14

Passive Humidity

Answer 14

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

Question 15

Active Humidify

Answer 15

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.

Question 16

Goals of Humidification

Answer 16

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

Question 17

Advantages of HME

Answer 17

Simple

Portable

Reduced Cost

Eliminates risk of electric shock

Question 18

Application of HME

Answer 18

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

Question 19

Contrindications of HME

Answer 19

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)

Question 20

Hygroscopic Condenser Humidifiers

Answer 20

• 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

Question 21

When Must Active Humidity Used

Answer 21

Bloody secretions

Thick, tenacious sputum

Hypothermia (core temp <32 °C)

Burn patients

Patients in which an HME is contraindicated for

Question 22

Component Required in Heated Humidity

Answer 22

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!

Question 23

Active Humidity-Heated Wires

Answer 23

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.

Question 24

Heated Wires Configuration

Answer 24

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

Question 25

Active Humidity-Water Traps

Answer 25

* 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.

Question 26

Where are Water Traps

Answer 26

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

Question 27

Active Humidity-Clinical Uses

Answer 27

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

Question 28

The New Technology Active Humidity Circuits

Answer 28

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

Question 29

Heated Humidity: Function of the Typical System

Answer 29

These are servo-controlled using a negative feedback system

Question 30

Heated Humidity: What Temperature

Answer 30

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!

Question 31

Humidication- Minimizing Contamination

Answer 31

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

Question 32

How to Minimize Circuit Contamination

Answer 32

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

Question 33

Minimize Circuit Changes

Answer 33

Current recommendation is no more than Q7d Avoid breaking the circuit unless absolutely necessary

Question 34

When to change an inline suction catheter

Answer 34

Only when the circuit is changes or equitment malfuntcion

Question 35

When to change a Yankeuer

Answer 35

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