Ventilators and Airway Monitors Flashcards
What are the 4 phases of the modern ventilator systems?
inspiration
transition from inspiration to expiration
Expiration
transition from expiration to inspiration
What type of pressure does the ventilator work by?
positive pressure ventilation
We are mainly concerned with inspiration operation as expiration is passive and is most dependent on what two factors?
airway resistance and lung compliance
What are the two main things that ventilators are classified by?
Their inspiratory phase characteristics and their cycling methods
What are the inspiratory characteristics?
constant flow, non constant flow, and constant pressure generators
What is constant flow (inspiratory characteristic)?
will deliver constant inspiratory gas flow regardless of airway circuit pressure within the 5-50psi
What is non constant flow (ins. characteristic)?
varying flow with each inspiratory cycle>dependent on what patient is doing
What is constant pressure generator (insp. characteristic)?
maintains constant airway pressure throughout inspiratory cycle regardless of insp. gas flow
Gas flow ceases when airway pressure=set insp. pressure
What are the 4 methods of cycling?
Time cycled
volume cycled
pressure cycled
flow cycled
What is time cycled?
Have a predetermined I:E
Cycle to the exp phase once a predetermined interval elapses fro the start of inspiration
TV is a product of the set insp. time and insp. flow are
What is volume cycle?
Will terminate inspiration when a set TV is reached.
**most adult. vent. are V-cycle but have a limit on insp. pressure to protect against barotrauma.
Does the patient always receive exactly the TV preselected?
No. A percentage of TV is always lost to the compliance of the system. Usually about 4-5 cc/cmH20
What is pressure cycled?
Will cycle into exp. phase when airway pressure reaches a preset pressure level.
TV and insp. time vary
What is flow cycled?
Uses pressure and flow sensors> this allows the vent. to monitor insp. flow at a preselected fixed insp. pressure.
When flow reaches the set level, the vent. will cycle from insp. to expiration
What types of anes. vent are classified as power source?
compressed gas-gas only
piston-power only
compressible bellows-gas and power
what types of anesth. vents are classified as drive mechanism?
Double circuit-bellows compressed by driving gas/ are pneumatically driven
Piston-bellows compressed by electricity
What is the most common type of vent that is used today and what are its characteristics?
Timed cycled, electronically controlled with a volume limiting aspect.
Describe what determines what type of bellow is used?
The direction of the bellows during EXPIRATION
**Descending-descending during expiration no longer used d/y gravity issues.
What happens to the bellows during expiration on the ascending bellow?
will ascend during expiratory phase.
Time is a parameter used to describe ventilation what does it entail?
Divded into insp. and expiratory periods or can be expressed as I:E
Expressed in SECONDS
**Used to define the number of resp. cycles within a given period of time.
Volume is a parameter used to describe ventilation what does it entail?
Measure of TV delivered to pt by then vent.
Expressed in ml
Expressed in L for minute volume
Volume of gas patient breaths.
Pressure is a parameter used to describe ventilation what does it entail?
Impedance to gas flow rate
Expressed in cmH20, mmHg, kPa
Pressure impedance is encountered in?
the breath circuit and
the pt’s airway and lungs
Flow rate is a parameter used to describe ventilation what does it entail?
rate at which the gas vol. is delivered to the pt.
**From the pt connection of the breathing system to the pt
Refers to volume change/time
Expressed in L/sec or L/min
What separates the driving gas from the patient gas circuit?
Bellows
During inspiration phase what happens the driving gas?
The driving gas enters the chamber and increases the pressure
The increase in pressure during the inspiratory phase caused by driving gas entering the chamber causes what 2 things to occur?
- The ventilator relief valve closes so no gas can escape into the scavenger system.
- The bellows are then compressed and then the gases in the bellows are delivered to the patient (like you squeezing the bag)
During expiration phase what happens to the bellows in relation to the driving gas?
the driving gas exits the bellows chambers and pressure within the bellow AND pilot drop to ZERO this causes the ventilator relief valve to open.
Why does exhaled pt gas fill the bellows before any scavenging occurs?
Because the valve ball produces a 2-3 cmH20 back pressure and therefore scavenging occurs ONLY when the bellows fill completely
True or False: The relief valve is ONLY open during expiration and any scavenging will occur at this point?
True
What are the ventilator setting used on the anesthesia machine?
TV: 6-8 ml/kg
RR: 8-12 bpm
Flow rate: 4-6X minute ventilation (MV=TV X RR)
I:E (1:2)
How can you calculate total inspiratory time TI?
TI=TV/Flow rate
How can you calculate total expiratory time TE?
insp. flow rate and RR/min
What is inspiratory pause/ sigh?
Making the patient take in the inspiratory volume and holding it and then exhaling (allows for recruitment of alveoli before they expire)
Volume of gas to pt is held in pts lung until exhalation begins
Inhalation time is increase by what percentage during inspiratory pause or sigh?
25%
What happens to the flow of gas drive and gas pressure in the bellows during insp. pause/ sigh?
Flow of drive gas stops.
Gas pressures in the bellow housing system stays the same.
If you added an inspiratory sigh would the time be taken out of the total insp. time or total exp. time?
Expiratory time
CO X O2 content will give you what physiological factor?
oxygen delivery
What is the equation for oxygen content?
(Hgb X %Sat X 1.39mlO2) + ( PaO2 X .0031mlO2)
Hypoventilation will reduce PaO2 EXCEPT in the case in which?
subject breath enriched O2 mixture
Each time you increase the FiO2 by 10% you are increasing the PaO2 by how much?
50 mmHg
What does the low pressure alarm (Disconnect alarm) detect?
Drop in peak circuit pressure
What does sub atmospheric pressure indicate?
Pressure of less than or equal to -10cmH20
***Pt is starting to breath against the machine (rebreathing)
What does a sustained/continuing pressure alarm indicate?
-15cmH20 for more than 10 seconds
What does high peak airway pressure alarm detect?
Detects excess pressure in the system activated at 60 cmH20 or at the practitioners setting.
What does the ventilator setting alarm indicate?
vent. inability to deliver the desired MV set.
What is the MOST important monitor on the machine?
Oxygen analyzer.
***Calibrated at 21% O2
What is a respirometer?
- Transducer cartridge and TV sensor clip
- Found on exp. limb
- Gas flow is converted to electrical pulse
What is the exhaled TV expected to be measured via respirometer?
Vt= Vt set on vent. + Vt fresh gas flow - Vt lost in system
True or False: Exhaled volume monitor is activated automatically once breaths are sensed and are ALWAYS active during mechanical ventilation?
True
True or False: Anesthesia driving gas never reaches the patient on an ICU ventilator?
True
Describe the CV mode of ventilation
controlled ventilation by vent.
Describe IMV mode of ventilation
Preset volume delivered at a specific interval while also providing continuously flow of gas for spontaneous ventilation.
- **Pt breaths spontaneously
- **Used as a weaning technique, fixed rate, NOT synched with pt.
Describe SIMV mode of ventilation
Same as IMV but SYNCHED with pts breath
- *Pt breaths spontaneously
- *Waking up a pt in the OR
Describe AC mode of ventilation
Intermittent mode of positive pressure ventilation. The pts inspiratory effort creates a sub-baseline pressure in the insp. limb and this then causes vent to deliver a PREDETERMINED TV.
- **If pts rate drops the vent will takes over in controlled vent mode.
- **All breaths are full assisted vent. breaths
Describe pressure support mode of ventilation
Aids in normal breathing with a predetermined level of positive airway pressure.
* Airway pressure is held constant through inspiration
What are the goals of pressure support ventilation mode?
To increase the pts spontaneous TV by delivering airway pressure to achieve volumes equal to 6-8ml/kg.
This will lead to :
Decreased WOB
Delays muscle fatigue
What is high frequency ventilation?
Low TV (less than dead space) with a high rate (60-300 bpm)
What are the typical settings for high frequency ventilation?
RR: 100-200 bpm
IT: 33%
Drive pressure: 15-30 psi
Goal: maintain pulm. gas exchange at lower mean airway pressures
Describe CPAP
Positive pressure is maintained during both inspiration and expiration.
*Only used when patient is spont. breathing
What caution is advised with CPAP usage?
Caution should be taken when using pressures > 15 cmH20. This can cause regurgitation and aspiration.
Define pressure controlled ventilation
Pt or time triggered pressure limited
**time cycled mode of vent. support
TV is NOT fixed
Used in situations where pressure can be high-useful in premies/neonates
What happens to gas flow in the cycle of pressure controlled ventilation?
Gas flow decreases as airway pressure rises and ceases when airway pressure equals the set peak inflation pressure
