Module 7 Flashcards
Duties of the anesthesia machine
Deliver Oxygen
Remove CO2
Must deliver inhalation agents & work in a rebreathing system
What are vents in the ICU?
Open circuit that don’t use absorbent & have gas warming & humidification techniques
Ventilator functions to
Remove carbon dioxide
Oxygenation is the
Intake of oxygen
Carbon dioxide elimination is dependent upon
Ventilation, with non CO2 containing gases & the amount of CO2 in the alveoli
The effects of oxygenation are best shown by
The partial pressure of oxygen in the arterial blood
How is oxygenation improved?
By adding oxygen to the inspired gas
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Physiological dead space is
Anatomical or Alveolar
What is dead space
The volume of ventilated air that doesn’t participate in gas exchange
Total dead space is called
Physiological dead space
What is anatomic dead space
The volume of air that fills the conducting zones of the respiratory airways, including the nose, trachea & bronchi; 30% of tidal volume
What is physiological dead space?
The volume of air ini the respiratory zone that doesn’t participate ini gas exchange
In the health adult, alveolar dead space is
Negligible
When does physiological dead space increase?
In lung disease states, making physiological dead space equal to anatomic dead space
Quantity of carbon dioxide produced dictates
Minute ventilation
What is the only method for eliminating carbon dioxide other than ECMO & cardio pulmonary bypass
Breathing
Spontaneous ventilation is normal conditions results in
PaCO2 of around 40
A normal person produces how much carbon dioxide/min?
200mL
What’s needed to maintained a normal CO2 level
Alveolar ventilation must be 200mLs/min, but anatomic dead space means ventilation must be at least 300mL to maintain 200mL of alveolar ventilation
Is ventilation essential for oxygenation?
No
How much oxygen does a normal adult person consume
250mL/min
When breathing oxygen, the pulmonary represents
Approximately 12 minutes worth of consumption
If connected to an oxygen supply, oxygen is unlimited & survival is limited by
Carbon dioxide accumulation, not hypoxia
What is the respiratory quotient?
Ratio between carbon dioxide production & oxygen consumption (0.8)
What is work of breathing
Work done to move gas into & out if the lung during spontaneous ventilation; this work is caused by the elastic properties of the kung & chest wall & the work needed to overcome resistance of the airways
The elasticity of the lung & chest wall is
Typically 70% of the total work of breathing
The force exerted by the ventilator is measures in
Pressure
Ventilator pressure is used to overcome
Compliance & resistance & the pressure results in tidal volume & inspiratory flow
Changes in tidal volume can be achieved by
Changes in inspiratory pressure or flow
When inspiratory flow matches tidal volume
Inspiratory pressure varies
When inspiratory flow matches pressure
The tidal volume varies
When utilizing volume mode
Peak pressure varies
When utilizing pressure mode
Tidal volume varies
Frequency, tidal volume, flow & I:E ration are all
Interdependent
Inspiratory pause is considered to be apart of the
Inspiratory phase
By adding inspiratory pause, time is consumed & flow rate
Will have to increase ini order to maintain the cycle time
If you change the expiration in the I:E ration
Something else must decrease
Endotracheal tube affects
Lung function by increasing resistance, the retention of secretions & lack of humidification (at the same time, lung function can be improved if there’s an upper airway obstruction & the tube provides conduit for ventilation)
Mechanical ventilation also causes
Consistent & predictable ventilation patterns & specific modes can improve ventilation/lung function
What are the pros & cons of suctioning?
Suction can remove secretions & improve oxygenation
Can cause harm by causing negative airway pressure, which can result in atelectasis
Positive pressure ventilation causes an increase in
Thoracic pressure, which can decrease blood flow & return the heart & cause decrease in cardiac output
Barotrauma is
Volumetrauma is
Too much pressure
Too much volume
Barotrauma & volumtrauma are manifested as
Pneumothorax or more suddenly by physiologic changes related to alveolar overstretching
Damage can be related to
Shear stress from opening & closing of the alveolar, corrected by heat but can increaser dead space & reduced cardiac output
Decreased compliance will result in
A greater share of the tidal volume & the effects of PEEP
Tidal volumes should be
6-8mL/kh
Maximal alveolar pressures, only slightly greater than 30-40cm of water are associated with
Lung injury, which causes alveolar damage, leading to pulmonary edema, activation of inflammatory cells & local production of inflammatory mediators, which are then leaked into systemic circulation
What can cause hypercapnia
Tidal volumes of 6mL/kg & low peak airway pressure
IRV ventilation can
Increase mean airway pressure & minimize peak airway pressures
Mean airway pressure corresponds to
Outfielder recruitment & increased oxygenation
Inadequate alveolar emptying can be the result of
Breath stacking & auto PEEP
Most ventilators utilize
Electricity or compressed gases to function
Ventilators that function solely on pneumatic gases are
Used in transport & ini MRI
Common drive mechanism are
Bellow & Piston
What are the 4 different types of drive mechanisms
Bellow
Piston
Turbine
Solenoids
Bellows are either
Ascending or Descending & are based on the movement during Exhalation
Which bellow is preferred
Ascending, since gravity doesn’t play a role; provides visibility
What pressure is used to to drive bellows
High pressure; 100% oxygen is used as driving gas, but it quickly utilizes oxygen reserve
if air is used as a driving gas & a perforation occurs…
Low oxygen concentration can occuree
The mixing of driving gas & circuit gas can
Dilute concentrations of inhaled anesthetics & cause hypoventilation
Piston ventilators use
An electric motor to drive piston to cause gas to flow, improving accuracy of tidal volume
A leak occurring at thee piston diaphragm can
Cause loss of circuit gs to the room & hypoventilation
Example of a Turbine ventilator
Drager
A turbine ventilator is a spinning turbine that
Produces a driving gas pressure
Higher RPM are associated with
Higher pressure
Turbine are required for
Control of circuit pressures, volume, & flows
A solenoid is a
Magnet wrapped by a coil of water
What is the key element in opening & closing the valve
Time, which then regulates gas flow
Solenoid have an
On/Off action
Servo uses an
Electrical motor to rotate a shaft that controls something else; they can be on/off, but are better utilized when they are finally controlling valves
A decelerating inspiratory flow has what advantages
Max pressure is minimized
Risk of barotrauma is decreased
Alveoli are kept expanded
Longer pressure plateau
Decreases venous return & cardiac output
Declining inspiratory flow
Allows time for gas redistribution at the end of inspiration
What is expiratory retard
Introduces a constricted orifice during exhalation so that the expiratory flow rate is slowed, which allows for more laminar flow & better emptying of the lung
Fresh gas typically flows
Continuously from the common gas outlet & some ventilators fresh gas flows directly into the ventilatory bellows
Gas compression is explained with Boyles Law
Increased pressure=decreased volume
For every 10cm of water
1% of volume is lost due to gas compression
Compliance of the anesthesia circuit
Causes volume losses by expanding hoses (why delivered tidal volume is frequently less than desired
n controlled breathing modes, the patient
Cannot contribute any effort towards the work of breathing
In controlled breathing if the volume is the fixed parameter
You are required to program the tidal volume, RR, & I:E ratio
What does the ventilator calculate?
Inspiratory time, flow from the respiratory rate & I:E ratio
Peak airway pressure is directly related to?
Airway resistance
Peak airway pressure is inversely related to?
Lung compliance
Worsening airway resistance & compliance can place the patient at risk for…
Barotrauma is no pressure limit is set
In the pressure control mode…
Pressure is fixed & peak airway pressure is set along with the respiratory rate & I:E ratio
The the pressure control mode, inspiratory pressure is varied to match
The set peak airway pressure
How is flow delivered in pressure co trip mode?
High flows are delivered at the start of inspiration & the flow is rapidly diminished while maintaining the pressure constant, leading to a longer time for gas redistribution.
Tidal volume is directly proportional to
Lung compliance
Tidal volume is inversely proportional to
Airway resistance
Assist & support modes means the patient & ventilator
Contribute to the work of breathing
Assisted & supported ventilation modes, while decreasing vent dysynchrony can
Facilitate the transition to spontaneous breathing while maintaining minute ventilation
Explain how assist control works
When the patient makes an effort to breath, the negative airway pressure triggers the ventilator to deliver a set tidal volume. As long as the patient triggers the vent more than a set rate, a controlled breath isn’t delivered
What is proportional assist ventilation?
Tidal volume correlates to the respiratory effort; the more negative pressure, the larger the tidal volume delivered
Explain pressure support ventilation
Pressure is equivalent of assist control ventilation; clinician sets peak airway pressure & the trigger (popular in the ICU)
Explain low pressure modes
Are believed to match the resistant effort of the inner tracheal tube, allowing tidal volumes to match the patients respiratory effort
Hat is intermittent mandatory ventilation
Patient is guaranteed a set number of mechanical breaths but between breaths, the he patient can spontaneously breath; these spontaneous breaths may be assisted, resulting in breath stacking & barotrauma
What mode of ventilation was created to prevent breath stacking
SIMV (synchronized intermittent mandatory ventilation)
A breath is delivered at the beginning/end & there’s an observation window that allows for spontaneous breathing. Any breath in the window is not a trigger for assist control or pressure support
CPAP modes are adjusted by
APL valve and I provide continuous positive airway pressure; same as adding PEEP
Utilizing APL CPAP can cause
Air trapping or worsening oxygenation & ventilation in patient with obstructing lung physiologic
High frequency ventilation is how many breaths/minute
150
What are the 3 types of high frequency ventilation modes
High frequency positive pressure
High frequency jet ventilation
Airway pressure release ventilation
High frequency positive pressure ventilation utilizes what and rates are…
Utilizes nasotracheal tube with small volumes at rates of 60-120 breaths/min; exhalation is passive and this is typically us r in airway & thoracic surgeries & may require special ventilator
High frequency jet ventilation is
For short term procedures that use a high pressure source of oxygen; done during emergency & suspension laryngoscopy; provide passive oxygenation during apnic periods; exhalation is passive & CO2 accumulation is common
The 2 major ventilators, Drager & GE display
Airway pressure
Time waveform
Numeric tidal volume & numeric peak airway pressure
GE ventilator uses
Bag in bottle configuration
What are the 2 gas circuits used in GE?
High pressure oxygen
Air to squeeze a visible ascending bellows
In the GE machine, the bellows are pushed down and cause
The gas contained in the bellows to be pushed through the CO2 absorber & mixes with fresh gas flow & continues through the inspiratory limb; exhaled gas is passed down to the expiratory limb & back to bellows via unidirectional valves; pressure must exceed 2.5cm of water during exhalation for valves to open; excess gas is sent to scavenging system preventing build up ; drive comes from the anesthesia machine pipeline or the cylinder supply
All Drager use
Piston ventilations
The piston allows for
Precise calculation of tidal volumes
Why is the ventilator in front of the unidirectional inspiratory valve
Decreases the compressible gas volume & increase accuracy of the tidal volume measurements
In the Drager, what happens when the machine is turned on?
APL valve is bypassed & has no effect
What is the purpose of the fresh gas decoupling valve
Closes during inspiration & prevents fresh gas flow from increasing tidal volume
What is the advantage of the piston drive ventilator
No gases are required for it to function which reduces cost & wasted gas
No automatic PEEP
High precision of the delivered tidal volume
Quiet
What are the disadvantages to piston ventilator?
The electric motor can wear out & fail & it’s hidden within the machine
It’s quiet
In the turbine ventilator
The fan can change RPM rapidly that delivers circuit pressure & flows; seeds of 70,000RPM
The turbine ventilator is depending on
Feedback with comes from accurate & precise system sensor measurements of time, pressure & flow ( ICU quality ventilation)
The servos use
A volume reflector & software control service to drive the gas modules & vaporizer; the volume reflector replaces the bag in a bottle design; can electrically function as a flow or pressure generator
What are the 2 most common ventilators
Bag in the bottle
Piston Driven
What causes over pressurization in the airway
Coughing
Excessive setting
When O2 valve is pressed during inspiration, sending pipeline O2 flow directly to the lungs ( this is prevented by pressure limits)
The ventilator can cause
Hypothermia
Dehydration
Drying of secretions
Incorrect settings causing hyper or hypocarbia secondary to excessive tidal volumes causing decreased preload
Obstruction hidden from view can decrease air flow
ICUs use an
Open system
What should be tested together to verify the excess of gas will be released once it he bellows are full to prevent sustained pressure
Scavenger system & ventilator relief valve
When the ventilator is active and no flows are on, the bellows…
Should NOT LEAK/lose volume
Explain the ascending gas drive ventilator or a bag in bottle type
The gas generates inspiratory flow similar to when an anesthetist squeezes the breathing bag, forcing air to move I. Th breathing circuit
Leaks in the bellows can cause
dilution it gas or loss of agent; without a means of escape, the addition of fresh gas flow into the breathing circuit would cause excessive volume & pressure
When does the ventilator relief valve open?
Only during expiration & releases gas to the scavenging system in an amount equal to the fresh gas flow per minute
Which bellows are safer? Hanging or standing?
Both are safe & capable of showing the user a disconnect as long as an appropriate monitor is used; when there’s a disconnect, easier to see in the ascending bellows (gravity)
What can decrease tidal volume in hanging bellows
Water gathering inside them
Piston driven ventilators don’t use a driving gas & therefore…
Will not deplete the oxygen cylinder during a pipeline failure
What is the driving force of the piston?
Electricity; if oxygen pipeline pressure fails, mechanical ventilation will continue
With turbine ventilators, inspiratory flow is generated by
Spinning impeller; tidal volume/inspiratory pressure is sensed by flow & pressure sensors; impeller spins at a slow speed continually, which facilitates spontaneous respirations & efficient gas mixing throughout the breathing circuit
What is the max pressure
40
Ventilators settings can contribute to
Lung injury
Atelectasis
Postoperative pulmonary complications
What are the goals of protection or open lung ventilation?
Prevent volumtrauma
Prevent barotrauma
Prevent lung inflammation due to alveolar wall stress
Minimize atelectasis & avoid hyperoxemia
What does volume control look like?
Even shark fins
What does pressure control look like?
Box with a slope
What does pressure support look like?
Box slope & dip
What does SIMV look like?
Quicker up slope, longer/ uneven down slope
In volume control ventilation the desired tidal volume is
Delivered at a constant flow
In volume control, the ventilator is volume limited &
Time cycled; inspiration is terminated when the desired tidal volume is delivered or is there’s an excessive pressure reached
In volume control, the peak inspiratory pressure is uncontrolled &
Rises as the patient compliance decreases ir airway pressure resistance increases
Tidal volume is adjusted to prevent atelectasis & respiratory rate is adjusted to
Keep end tidal CO2 at the desired level
What are the best tidal volumes and what is most effective to avoids atelectasis & ventilator induced lung injury?
5-7ml/kg
PEEP & alveolar recruitment maneuver
In pressure controlled ventilation
The max pressure is set & the cycle is controlled by the time with a decelerating flow pattern
In a decelerating flow pattern
Inspiratory flow is strongest early in inspiration to reach the set pressure quickly & then declines the flow just sufficient to maintain the set pressure although this can increase mean airway pressure & may decrease venous return & cardiac output
Tidal volume is uncontrolled & changes
As compliance or resistance changes
What happens in Katie to with low compliance such as obese
Pressure control may result in increased tidal volume at lower peak airway pressures compared to volume control ventilation.
SIMV can be either
Pressure or volume based & can be used for full or partial support
Why was pressure control ventilation with volume guarantee created?
To address the problem that tidal volume & pressure modes vary
How does pressure control ventilation with volume guarantee work
Delivers a volume breath at the set tidal volume determining the patients compliance & then the inspiratory pressure can be adjusted for the next breath
Pressure support is responsible for
Patients efforts delivering pressure to the airway once effort is sensed, thus ONLY useful for patients who are spontaneously breathing
Is there a minimum minute ventilation in pressure support
No, even though some allow backup apnea setting
What vent mode is helpful during maintenance or emergence?
PSV
How do you use CPAP mode
Select PSV mode but adjust pressure to 0 & then add PEEP
PEEP prevents
Airway & Alveolar collapse, atelectasis
Mai rains functional residual capacity
Does CPAP assist with ventilation?
No
Why do modern ventilators have large tidal volume ranges
Greatly increased accuracy of the tidal volume delivered
Compensation or decoupling of fresh gas flow, especially when small tidal volumes are utilized for PEDs
Fresh gas decoupling or tidal volume compensation allows for
Much more accurate delivery volume
Is tidal volume accuracy a problem in pressure control
No
What is the most common preventable ventilator mishap
Disconnection
Most common site for disconnection
Between the breathing circuit & endotracheal tube at the Y piece
What electronic monitors monitor of leaks
Capnography & pressure volume based alarms
What is the common mistake after intubation
Failure to initiate ventilation
What is the first step of MB is suspected?
Withdrawal the triggering agent
What else can be done with MH?
Hyperventilate with 100% oxygen
Increasing fresh gas flows
Changing circuit components & granules
How long should you flush line for MH
10L for 20 minutes
104/ minutes
