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Anethesia > Ventilators and Airway Monitors > Flashcards

Ventilators and Airway Monitors Flashcards

1
Q

Venitalors

A

ICU ventilators are more powerful than OR ventilators
Anesthesia = we rebreathe the gases
ICU = every breath is a fresh breath and oxygen is cheap and anesthesia gases are not
Classified mainly according to their inspiratory phase characteristics and their method of cycling

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2
Q

Modern Ventilators

A

Positive pressure ventilation
4 phases:
1) Inspiration
2) Transition from inspiration to expiration
3) Expiration
4) Transition from expiration to inspiration
We are mostly concerned how they operate during INSPIRATION as expiration is passive and depends on airway resistance and lung compliance.

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3
Q

Inspiratory Characteristics - Constant Flow

A 
Constant Flow: deliver a constant inspiratory gas flow regardless of airway circuit pressure. 
High pressure changes in a airway resistance or compliance
Low pressure (venturi) gas source varies to some degree with airway pressure
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4
Q

Inspiratory Characteristics = Nonstant Flow and Constant Pressure Generators

A

Nonconstant: consistently cary flow with teach inspiratory cycle.
Constant pressure generators: maintains a constant airway pressure throughout inspiratory. Irrespective of inspiratory gas flow. Gas flow ceases when a airway pressure equals the set inspiratory pressure

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5
Q

Methods of Cycling: Time and Volume

A

Time: cycle to the expiratory phase once a predetermined interval elapses from the start of inspiration. TV is a product of the set inspiratory time and inspiratory flow rate.
Volume: terminates inspiration when a pre-selected TV is delivered. Most adult ventilators are volume cycled but have a second limit on inspiration. Pressure to guard against barotrauma. A percentage of TV is always lost to the compliance of the system. Usually about 4-5 mL/cm H2O

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6
Q

I/E Ratio:

A

Normal physiological condition I/E: 1:2 or 2:4. Total time spent inspiration/expiration = 6 seconds. Each respiratory = 6 seconds average
Set TV on ventilator. Set in and deliver and not matter what time and switch to expiratory once volume has been delivered.

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7
Q

Methods of Cycling: Pressure cycled and Flow Cycled

A

Cycle: into expiratory phase when airway pressure reaches a pre-determined level. TV and inspiratory time vary.
Flow: Have pressure and flow sensors that allow the ventilator to monitor inspiratory flow at a pre-selected fixed inspiratory pressure. When this flow reaches a pre-determined level, the ventilator cycles from inspiration to expiration.

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8
Q

Classification of Anesthesia Ventilators

A

Power source:
Compressed gas: gas only
Piston: power only
Compressible bellows: Gas and power
Drive Mechanisms:
Double circuit - bellows compressed by driving gas and pneumatically driven
Piston - bellows compressed by electricity.

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9
Q

Classification of Anesthesia Ventilators

A

Cycle mechanisms: on older machines. Most our ventilators are time cycled, electronically controlled with a volume limiting aspect.
Bellows: direction of bellow movement during EXPIRATION determines this classification.
Ascending: ascend during expiratory phase
Descending: descend during expiratory phase

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10
Q

Parameters Used to Describe Ventilation: Time

A

Time:
Divided into inspiratory and expiratory periods
Expressed in seconds
Or by relation of inspiratory time to expiratory time and expressed as I:E ratio
Used to define the number of respiratory cycles within a given time period
Don’t forget to convert minutes to seconds!
3 seconds in inspiratory and 6 seconds on expiratory I:E ratio: 1:2

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11
Q

Parameters Used to Describe Ventilation: Volume

A 
Volume:
Measure of tidal volume delivered by the ventilator to the patient
Volume of gas patient breaths
Expressed in mL/sec
Expressed in L/minute volume
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12
Q

Parameters Used to Describe Ventilation: Pressure

A 
Pressure:
Impedance to gas flow rate
Impedance encountered in:
1) Breathing circuit
2) Patient's airway and lungs
Amount of backpressure generated as a result of:
1) Airway resistance
2) Lung-Thorax Compliance
Expressed in cm H2O, mmHg or kPa
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13
Q

End Tidal CO2

A

Gold standard for how well you are ventilating the patient!
Patient can’t tolerate the higher pressure: give them more volume? How? Limiting pressure = prolong expiratory phase? Limit pressure = lung disease and don’t want PEEP passed 20 cm = increase the RR instead. Reduce the volume.

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14
Q

Preoxygenate Patient

A

Why? Intubate in lab and took longer too intubate? Once tube is in ventilator states high CO2 due to buildup? Does the saturation change? No!

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15
Q

Parameters Used to Describe Ventilation: Flow Rate

A

Flow Rate:
Rate at which the gas volume is delivered to the patient
from the patient connection of the breathing system to the patient
Refers to the volume change/time
Expressed in L/sec or L/min

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16
Q

Minute Ventilation

A

Flow rate = what the machine sets in order to deliver what you dial in. 5 Times greater than what you dial in. Minute ventilation is 5L/min = 25L
Ventilator does not work until you have proper flow rate

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17
Q

How does the Ventilator Work?

A

Bellows separate the driving gas from the patient gas circuit
During inspiration phase, the driving gas enters the chamber and increases pressure.
The above increase in pressure causes 2 things to occur:
1) Ventilator relief valve closes - so no gas can escape into the scavenger
2) The bellows are then compressed and the gases in the bellows are delivered to the patient (analogous to you squeezing the bag)

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18
Q

Bellows

A

Gas in the bellow never meets the patient. Gas inside the below is what the patient breaths in and out. Gas outside the chambers is what drives the bellow in and out.
They never mix. Gas inside the bellow + anesthestics gas is what the patient gets
Bellows are driven by the gas: separate from the gas patient is breathing

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19
Q

Bellows: Inspiration
Bellow chamber collapses
Relief Valve CLOSED

A

Inspiration phase causes 2 things to happen

1) Relief valve will close. It will close to prevent gas lost to the scavenger system because its lower pressure system
2) APL open = gas goes to the scavenger.
3) Once pressure is generated the valve will close. It prevents it going to the scavenger = need pressure to go into the patient.
4) Bellows compressed: squeezing the bag to deliver gas

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20
Q

Bellows: Expiration
Bellows chamber expands
Relief Valve OPEN
SCAVENGER SYSTEM!

A

During Expiration:
The drive gas exits the bellow chamber, the pressure within the bellow and pilot drop to zero causing the ventilator relief valve (ball type) to open.
Exhaled patient gas fills the bellows before any scavenging occurs because the valve ball produces 2-3 cm H2O back pressure - scavenging occurs ONLY when the bellow is filled completely. Excess goes to the scavenger.
The relief valve is ONLY OPEN during EXPIRATION, and scavenging occurs at this point.

21
Q

CO2 Absorber

A

CO2 absorbed when the patient takes the next breath = counterintuitive. Absorbed by CO2 upon inhalation or kill the absorber and then patient will then rebreathe CO2.
All machines designed to give CO2 = free gas on inspiration and not expiration!
Start fresh CO2 canister beginning of the day

22
Q

Tidal Volume

A

Set ventilator to deliver 500 mL to patient. TV on the dial and notice on expiration how much volume you are getting back. Not the same as what you dial in due to lost of volume due to the system.
Set volumes = equal to bellow + fresh gas flow = given exact TV
Elastic: lost alot of air to the system

23
Q

Typical Ventilator Settings

A

Tidal Volume: 10-15 mL/kg
RR: 8-12 min
Flow rate: 4-6 x minute ventilation
MV = TV X RR
I:E Ratio: physiologic is 1:2
Calculate TI (time in inspiration): TV/Flow Rate
TE (time in expiration): determined by inspiratory flow rate and RR/min

24
Q

Recruit Aveoli

A

Physiologic respiration 10-14. Stay at lower RR and use extra volume to recruit alveoli. Better practice to give bigger volume to recruit alveoli.

25
Q

Inspiratory Pause/Sigh

A

Inspiratory Pause: spend more time in inspiration. Machine sigh. Patient take a breath in and hold it in 25% of the time and then exhale.
Poor man peep: breathe and recruit alveoli before they expire.
Taking time away from the expiration. 25% more time on inspiration and expiration time is shaved. Must adjust expiration time to fix it.

26
Q

Ventilator Setting: Minute Ventilation

A

Dial in volume and rate. Volume: 500 mL and rate: 10. The machine will alarm. In order for the ventilator to work, 5 times the minute ventilator needed. Turn the volume 5 times to match the machine. Newer machine: dial in volume and rate = no inspiratory flow rate. It internally calculates it.

27
Q

Newer Ventilators

A

Dial in volume, rate and I/E ratio.

Limiting pressure 35-45 mmHg; anything higher = barotrauma

28
Q

Physiologic Factors: FiO2

A

Oxygen delivery = CO X O2 content
Oxygen content = (hgb x %sat x 1.39 mL O2) + (PaO2 x 0.0031 mL O2)
1 gram of pure hemoglobin combines with 1.39 mL of O2
For each mmHg of PaO2 = 0.0031 mL O2/100 mL blood)
Arterial blood with PO2 = 100 mm Hg contains 0.3 mL of O2/100 mL

29
Q

How much O2 Do we give?

A

Factors to consider:
1) Hypoventilation reduces PaO2 except when the subject breathes enriched O2 mixture
2) PaO2 = (PIO2 - PaCO2) / (R+F)
3) R = extraction ratio (0.8)
4) F = correction factor (small and negligible)
It’s okay to give 100% O2 for a short period of time.

30
Q

FiO2 and SaO2

A 
Each time you increase FiO2 by 10%, you increase PaO2 by 50 mmHg
PaO2         FiO2
100            21%
150            30%
200           40%
250           50%
31
Q

Ventilator Alarms

A

Low Pressure: disconnect alarm detected by a drop in peak circuit pressure
Sub atmospheric pressure alarm: pressure of less than or equal to -10 cm H2O
Sustained/continuing pressure alarm: 15 cm H20 or more than 10 seconds
High peak airway pressure alarms: detects excess pressure in the system activated by 60 cm H2O or set by practitioner; APL valve closed = continuous pressure
Low oxygen supply alarm

32
Q

Monitors

A

ETCO2 monitor: capnography best for revealing a disconnect
Oxygen analyzer: most important monitor on the machine. Calibrate it 21% O2 = room air
Respirometer: ventilator setting, PAP monitors
Viginlace is the best monitoring you can have

33
Q

Respirometer

A

How much volume giving and how much pressure is coming back
Transducer cartilage and tidal volume sensor clip
Gas flow converted to electrical impulses
Cartridge is on the expiratory limb
Sensor clip snaps onto transducer cartridge
Exhaled volume expect to measure is:
Vt= Vt set on ventilator + Vt fresh gas flow - Vt lost in system
Expiratory limb: calculates how much oxygen and gas coming back
Not exactly what you set is the same amount you get back!

34
Q

Respirometer

A

Exhaled Volume Monitor: activated automatically once breaths are sensed and always active during mechanical ventilation.
Reverse Flow: alarm if flow towards patient
Apnea: if sufficient breath, based on TV settings, not achieved within 30 seconds
Low Minute Ventilation
Always on the expiratory limb!

35
Q

ICU Ventilators vs Anesthesia Ventilators

A

ICU ventilators:
Are more powerful allowing for greater inspiratory pressure and tidal volume
Support more modes of ventilation = changes
Gas supplied by the ventilator directly ventilates the patient
Anesthesia machine:
CO2 absorber
Driving gas never reaches the patient. 100% O2 in old machines; Air/100% O2 in newer machines
Bellows are essential; gas comes in to drive the bellow is different than what the patient is breathing!

36
Q

Modes of Ventilation: Control and IMV

A

CV: controlled ventilation by ventilator.
IMV (intermittent mandatory ventilator):
1) Ventilator delivers a preset volume at specific interval while also providing a continuous flow of gas for spontaneous ventilation.
2) The patient breaths spontaneously while the ventilator delivers a preset TV at a pre-determined interval through a parallel ventilator circuit.
3) Used as a weaning technique
(a) fixed rate; (b) NOT synced with patient

37
Q

Modes of Ventilation: SIMV

A

Like IMV but synced with patient’s effort. The patient breaths spontaneously and at a pre-determined interval the spontaneous breath is assisted by the machine.
It times the mechanical breath with the BEGINNING of a spontaneous effort. Waking patient in the OR.
Detects patient is inspiring and generation rest of inspiration.

38
Q

Modes of Ventilation: SIMV

A

SIMV mode provides ventilatory assistance during times when a patient may have the ability to breath but lacks either the required rate or tidal volume. The patient can trigger a mechanical breath of the pre-set TV within a trigger window. In this way, mandatory breaths are synchronized with spontaneous effort. Triggered breaths are indicated by a color change on the pressure curve and ca e also monitored on the trend curve.

39
Q

Modes of Ventilation: AC

A

Intermittent mode of positive pressure ventilation. The patient’s inspiratory effort creates a sub-baseline pressure in the inspiratory limb of the ventilator circuit that then triggers the ventilator to deliver a pre-determined TV.
If the patient’s rate drops below a preset minimum rate, the machine takes over with controlled ventilator mode.
All breaths the patient takes are a full assisted ventilator breaths.
SIMV and IMV: volume control ONLY!
AC: either volume or pressure
Set rate and the rate drops below RR: 10 give some breaths

40
Q

Modes of Ventilation: Pressure Support

A

Aid in normal breathing with a pre-determined level of positive airway pressure.
Similar to IMV except that airway pressure is held constant through out the inspiratory period.
The objective is to increase the patient’s spontaneous TV by delivering airway pressure to achieve volume equal to 10-12 mL/kg.
Decreases work of breathing
Delays muscle fatigue

41
Q

Pressure

A

Aids in normal breathing with positive pressure
LMA: limit pressure maximum 8-9
Bagging the patient = mask bagging a patient to the OR: Careful in the beginning. Stop breathing = normal. Don’t generate too much pressure, putting air into the belly.
Give a breath, take a minute. Don’t generate too much pressure = pressure limit to 10-15

42
Q

Modes of Ventilation: High Frequency

A

High frequency ventilation: oscillator, jet ventilator
Used in renal stones. Time shock with PR interval to prevent shock with cardiac cycle. Lungs allow large volume in the lungs shift the stones up or down. Stones is moving. JET ventilation minimizes the movement of kidney stones so that surgeon can hit the stones with the shock
Giving 100-300 breaths per minute. Caution: have to allow for exhalation. Rapid firing tidal volume = exhalation so that patient doesn’t get barotrauma.
Give lots of breaths = allow for expiration or allow intermittent depending on the speed

43
Q

Modes of Ventilation: High Frequency

A

Low tidal volume, less dead space with a high rate (60-300 bpm)
Typical setting: 100-200 bpm
IT: 33%
Drive pressure: 15-30 psi
Goal: maintain pulmonary gas exchange at lower mean airway pressure. Used in ESWL? Kidney stones
Tracheal pressure: don’t go above 15.

44
Q

Modes of Ventilation: Pressure Control Volume

A

Patient or time triggered pressure limited, time-cycled mode of ventilatory support.
Gas flow decreases as airway pressure rises and ceases when airway pressure equals the set peak inflation pressure
TV is not fixed
Used in situation where pressure can be high
Useful in neonatespremises

45
Q

Modes of Ventilation: Pressure Control Volume

A

Machine delivers 10 pressure and stop ventilation and go into expiration.
Little volume based on pressure.
Neonates or premature: limit the pressure coming into the patient to compensate what could become barotrauma
Often times = lap surgery fill the belly with CO2. Tolerate high PEEP pressure - fighting against CO2 in belly
Pressure limiting if the patient is sicker

46
Q

Modes of Ventilation: PCV

A

In the PCV mode, the ventilator builds up the patient’s circuit pressure to a given level and maintains the pressure until the expiration phase.
The inspiratory flow is decelerating and optimized to provide the set pressure limit as quickly as possible (adjusted automatically).
There is no measurement of volume in PCV. Use of volume monitor is therefore required.

47
Q

Modes of Ventilation: CPAP

A

Continous positive pressure airway pressure
Positive pressure is maintained during both inspiration and expiration. Only when the patient is spontaneously breathing.
Can be provided with mask
Caution: if pressure > 15 cm H2O, can cause regurgitation and aspiration.

48
Q

Modes of Ventilation: CPA and Obesity

A

CPAP = used for apnea. Anesthetize a patient with CPAP and told in pre-op and need to use it before night of anesthesia and after anesthesia.
Have to use it before and after!
Narcotic prescription = have to use it while on those!

Anethesia (6 decks)

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