E3- Anesthesia Ventilators Flashcards
A ventilator is an automatic device that will provide what two things to the patient?
- Patient ventilation
- Patient oxygenation
On the anesthesia workstation, ventilators essentially replace what component?
- The green reservoir bag
What ventilation was available from old ventilator models?
- Only offered volume-controlled ventilation
- No PEEP
- Couldn’t provide high enough PIP
- Only controlled mandatory ventilation
Barotrauma is an injury that results from ______
- Injury resulting from high airway pressures
- Limit PIP to avoid this
Compliance
- Ratio of a change in volume to a change in pressure
- decrease in compliance causes decrease in ________ bc volume used to expand system (volume controlled)
- newer vents alter volume delivered to compensate for ____________________ (pressure controlled)
- Vt
- system compliance
Work of Breathing
o Energy expended by the patient/ventilator to move gas in + out of lungs.
Exhaust Valve
Valve that opens to allow driving gas to exit the bellows housing during inhalation
What is Fresh Gas Compensation?
- a way to prevent FGF from affecting tidal volume
- by measuring tidal volume and adjusting the volume of gas delivered by the ventilar.
The time during which lungs are held inflated at a fixed volume and pressure.
- Inspiratory pause time
- inspiratory platuea
Increase intrathroacic P –> dec preload –> dec CO !!
I:E ratio
- Ratio of the inspiratory phase time to the expiratory phase time
Normal I:E Ratio
- 1:2
- We spend more time expiring
intrathoracic p > dec preload > dec CO – decrease I:E to 1:1 to help CO
Inverse ratio ventilation
- Inspiratory phase time is longer than the expiratory phase time
- 2:1
The sum of all tidal volumes in one minute
- Minute volume
Peak Pressure
- The maximum pressure during the inspiratory phase time
- PIP
Spill Valve
- The valve in the ventilator that allows excess gases to be sent to scavenging system during exhalation
The energy that the patient/ventilator expends to move gas in and out of the lungs.
- Work of breathing
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Factors that affect delivered tidal volume.
- Fresh gas flow
- Compliance
- Leak
On older vents, as FGF increases, what happens to tidal volume?
* what do newer vents do to excess FGF?
- Tidal volume increase
- diverted during inspiration
How do newer vents compensate for system compliance?
- New vents will alter the volume delivered to compensate for system compliance (pressure control)
2 compliance factors affecting ventilation
o System – bent tube, step on circuit
o patient – asthma, COPD, Trendelenburg, supine, laparoscopy CO2 insufflation
How does a leak affect delivered tidal volume?
- Leaks around ETT or LMA
- will cause a decrease tidal volume that can’t be compensated by the ventilator
Components to the bellows ventilator.
- Driving gas supply + FGF
- Controls
- Alarms
- Pressure-limiting mechanism
- Bellows (accordion-like device)
- Housing
- Exhaust Valve
Components of Bellows Ventilators
What does the driving gas + FGF do to the bellows?
What is another name for this?
- The driving gas is the gas external to the bellows that cause them to collapse.
- FGF is internal the bellows + delivered to pt
- Double Circuit
Components of Bellows Ventilators
FGF is oxygen, air or mix + in the bellows it is equal to?
If oxygen using, what is flow from flowmeters + Vm from FGF?
- Vm
- flow control from flowmeters (1-2 L/min) + Vm from FGF (4-5 L/min)
Components of Bellows Ventilators
What are the two required alarms on the ventilator?
- Low-pressure alarm
- High-pressure alarm
- high, medium, + low priorities
Components of Bellows Ventilators
What is the most common cause of low-pressure ventilator alarms?
- Disconnection of a circuit
Components of Bellows Ventilators
What are examples of high-pressure ventilator alarms?
- Kinking of the ETT
- Occlusion of mask
Components of Bellows Ventilators
What is the pressure limiting mechanism?
What is a good set point for the pressure limit of the inspiratory pressure?
- Limits inspiratory pressure
- 10 cmH2O above average inspiratory pressure with desired Vt
Components of Bellows Ventilators
What is the housing of the anesthesia machine?
- Clear plastic cylinder
- Allows movement of bellows to be observed
- Has scale on side for rough estimation of tidal volume
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What is the function of the exhaust valve?
- Communicates with the housing and allows driving gas to be vented to the atmosphere on exhalation
The bellows is _______ driven
pneumatically
What are the two kinds of bellows?
Which one is safer?
How are they named?
- Ascending Bellows (standing) safer
- Descending Bellows (hanging)
- named on what they’re doing during exhalation
Why are ascending bellows considered safer?
- disconnection in circuit,»_space; bellows will fail to rise on exhalation»_space; trigger CRNA to know something is wrong.
- For descending bellows = continue to descend even if disconnection d/t gravity
What are the 3 bellows problems?
What do they lead to?
- Improper seating of bellows inside housing»_space; inadequate ventilation
- Hole»_space; alveolar hyperinflation / barotrauma
- Scavenging system closed»_space; waste gases vented to room
Hole in bellows :: if driving gas is O2 vs. air
- if driving gas is O2 - increase FiO2
- if air - dcrease FiO2
What are the components of Piston Ventilators?
- mechanically driven motor (plunger of syringe)
- no driving gas - single circuit
- use less gas
PIston ventilators don’t alter ______ based on compliance.
Vt
Piston ventilator 4 extras
o Very small piston chamber
o Accurate tidal volumes
o Hidden on machine…no visual ventilation
o Very quiet
What are 2 piston problems
- refills even with disconnection
- entrain room air during leaks»_space; dilutes O2/volatiles
3 controlled ventilation modes
- volume control
- pressure control
- volume guarantee pressure-control
What is the most commonly used mode of ventilation?
- Volume control
What is volume control mode of ventilation?
- Preset tidal volume is delivered (fixed parameter)
- Additional breaths = at machine preset Vt
any RR is always with set Vt - RR 10 + Vt 500 ,, RR 20 + Vt 500
Volume control mode can cause excessive ________ pressure.
- inspiratory
Volume control mode will have set:
- Set Tidal Volume
- Set Respiratory Rate
- Set I:E Ratio
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What conditions would a volume control mode not be beneficial for the patient?
- Conditions with decreased compliance and FRC
- Obese/Pregnant patients
- Trendelenburg/Lithotomy procedures
- Patients with lung pathology
- Patients that need to be weaned from the vent
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How much tidal volume should be delivered to a patient on a ventilator?
- 4-6 mL/kg
Describe pressure control ventilation.
- Preset inspiratory pressure is quickly achieved during inspiration.
- Set PIP, RR, and I:E Ratio
Describe tidal volume with pressure control ventilation.
- Tidal volume varies with resistance and compliance
*Insufflation + Trendelenburg»_space; cause low Vt *
What will insufflation of the abdomen do to inspiratory pressure?
- Increase inspiratory pressure, which will cause a low tidal volume.
What is the good thing about pressure control ventilation?
- This vent setting protects lungs from barotrauma of excess pressure
What is the bad thing about pressure control ventilation?
- The pressure delivered in this mode might not develop enough tidal volume for the patient.
- Increase risk for atelectasis
- cause hypoventilation
What are ways to deliver more tidal volume in pressure control ventilation mode to patients with low lung compliance?
- Increase PIP
- Use Inverse I:E ratio, longer inspiration than expiratory time. The body will have time to adapt to increased pressure.
Describe Volume Guarantee Pressure-Control.
- Maintain Tidal Volume by adjusting PIP over several breaths.
- Prevent sudden Tidal Volume changes d/t compliance
- Lost insufflation - *change in compliance when case finishing up *
What is Assist Control Ventilation?
- Predetermined negative pressure will trigger breath
- Breath is preset tidal volume
set paramter 8 RR + 600 Vt — pt triggers 10 RR @ 600 ea
What is Intermittent Mandatory Ventilation (IMV)?
- Mandatory ventilator breath is set - RR is set
- Additional native breaths at** variable tidal volume**
- Allows breath stacking
What is SIMV?
- Synchronizes ventilatory-driven breaths with spontaneous breaths
- makes a waiting time before the next breath + pt has to exhale - no stacking
- Provides backup to weaning ventilator
- Best for weaning
What is Pressure Support?
*** PIP + inspiratory time **set
* Vt equates to the native effort
* Need apnea alarm
- standard machines have variable amts of __________ substances
What are ways to use a ventilator during an MRI?
FERROMAGNETIC
- MRI compatible machines
- Anesthesia machine kept outside in hallway
- Machine bolted to wall
- Aluminum tanks or pipeline gas supply
General Hazards: What 4 can cause ventilation failure?
- Disconnection from power supply
- Extremely high FGF
- Fluid in electronic circuitry
- Leaking bellows housing
FIX = Bag the pt
General Hazards: How can there be a loss of breathing system gas?
- Failure to occlude spill valve
- Leak in the system
Need to do daily anesthesia machine check
General Hazards: What 4 can cause incorrect ventilator settings?
- Inadvertent bumping
- Not adjusted for new case
- Not adjusted for position/pressure changes
- Ventilator turned off for xrays (cholangiogram)
3 Advantages of a ventilator
- Allows anesthesia provider to devote energy to other tasks (free hands)
- Decreases fatigue
- Produces more regular rate, rhythm, and Vt
6 Disadvantages of a ventilator
- Loss of “feel” (reservoir bag)
- Older versions may not have all the desired modes
- Components are hard to clean or fix
- Lack user-friendliness
- Noisy or too quiet
- May require high-flow driving gases…expensive
What is the trace gas concentration?
- Concentration of a gas far below that needed for anesthesia or detected by smell
Trace concentration units
- PPM (parts per million)
100% of gas is how many PPM?
1,000,000, PPM
1% of gas is how many PPM?
10,000 ppm
Higher levels of trace gas concentration are seen in… 3
- Pediatric anesthesia
- Dental surgery
- Poorly vented PACU’s
Chart from NIOSH 1977 - maximums of how much ppm allowed
1. halogenated agent alone?
1. nitrous oxide?
1. combination - halogenated?
1. combination - nitrou oxide?
1. Dental facilitites (nitrous oxide alone)?
- 2
- 25
- 0.5
- 25
- 50
6 causes for operating room contamination
- failutre to turn off vaporizer
- poor fitting mask
- flushing circuit into room
- spilling when fill vaporizer
- uncuffed ETT
- scavenging system leaks
For years what did old studies conclude about trace gas exposure?
- Spontaneous abortions
- Spontaneous abortion in spouses
- Infertility
- Birth defects
- Impaired performance
- Cancer/mortality
- Liver disease
- Cardiac disease
These negative side effects of gas exposure has been mitigated with the scavenger system
Scavenging system function.
- Removes the collection of gases from equipment used to administer anesthesia or exhaled by the patient.
- removal of these gases outside the work environment
Describe the passive scavenging system.
- attached to room ventilation system
- Entire volume is exhausted to the atmosphere.
- Disposal tubing from the anesthesia machine is attached to the exhaust grilland removed with room air.
Very economic – uncommon :(
Describe the active scavenging system.
- Attached to central vacuum system
- Must be able to provide high volume (30L/min)
- Need plenty of suction outlets and close to anesthesia machine
COMMON
5 Ways to alter work practices + not contaminate the OR
- mask fit
- turn off gas flow durign intubation
- 100% wash out at end of case
- prevent liquid spills
- plase anesthesia machine close to exhaust grill - passive system
7 causes of hypoxic inspired gas mixture
- Incorrect gas in pipeline
- Incorrectly installed outlets
- Oxygen tubing or hoses attached to incorrect flow meter
- Incorrect cylinder attached to yoke
- Incorrect cylinder…..around world O2 is green, white, blue, and black
- Flow control malfunction
- Leak in oxygen flow meter
How can the ventilator cause hypercapnia? 4
- Hypoventilation
- Absorbent failure (exhaustion)
- Excessive dead space
- Defect coaxial system - mapleson D
How does an anesthetic agent overdose over with the anesthesia machine? 5
- Tipped vaporizer - lots of liquid
- Vaporizer accidentally on
- Incorrect agent in vaporizer
- Interlock system failure
- Overfilled vaporizer
How does Hypoventilation occur on the ventilator?
- Insufficient gas : swithc from pipeline to cylinder
- Obstruction
- Leaks
- Main machine power off
- Breathing system leaks (disconnections)
What are 6 ways to prevent inadvertent exposure to volatiles?
MH , severe nv pts
- Change breathing system hoses and bag
- Change fresh gas supply hose
- Change absorbent
- Use very high oxygen flows to flush the machine
- Remove vaporizers
- Use an axillary flowmeter for supplemental oxygen
2 Causes of blocked inspiratory + expiratory paths?
- mask wrapping
- absorbent wrapping
