6. Ventilators – Flashcards
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How are ventilators an integral component of the anesthesia machine?
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-Vital role of ventilation and frees the hands of the anesthetist -Compensates for lung compliance -Control CO2 levels
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What is the best way to verify adequate ventilation?
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ETCO2
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How were early ventilators built?
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Hand and bag
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What kind of ventilators were early ventilators? -What kind of improvement was made? -What do we have now?
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-Earliest ventilators were volume ventilators (Omega 7000 and Ohmeda 7800) -Some later models both volume and pressure modes -Modern ventilators have both
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How are anesthesia ventilators different than ICU ventilators?
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ICU ventilators have an unlimited supply of gas, so you can't re-breathe the gas (Open circuit) Anesthesia ventilator is limited by the patient chamber, easy to re-breathe gases (Closed circuit)
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What were contemporary gas-driven ventilators known as?
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"Bag-in-a-bottle"
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What kind of adjustments were made to make an old ventilator into a newer model of ventilator?
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-Reservoir bag replaced by bellows -APL (pop-off) valve replaced by a ventilator pressure relief valve (spill valve) -Anesthetist's hand replaced by the pressure of the driving gas
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What are some of the characteristics of a piston ventilator? -How is the air moved? -Driving gas? -Single/Double circuit?
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-Electric motor is pushing a piston which is then used to send gases to the patient -No driving gas -Single circuit ventilator (Bellow ventilators are double circuit ventilators)
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Which circuit is present on a single-circuit ventilator?
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-Patient circuit only -Electrical powering for everything else
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What are some characteristics of turbine ventilators? -Good/Bad? -Breathing work and ability? -What type of patients can it support? -Similarities to ICU ventilators?
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-Efficient - generates inspiratory flow very quickly -Low work of breathing -Spontaneous breathing any time -Supports all patients -Similar to high-end ICU respirators and performs all common ventilation modes that are used in the ICU
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How can different anesthesia ventilators be classified?
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-Power source -Drive mechanism -Cycling mechanism
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How are anesthesia ventilators classified by power source?
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Can be a compressed gas (older ventilators), electricity (piston), or a combination of both (modern)
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How are anesthesia ventilators classified by drive mechanism?
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Pneumatically driven double-circuit (gas drive circuit pushing the bellows and a patient circuit hooked up to the breathing system). Driving gas can be oxygen, air, or a combination of O2 and air
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How are anesthesia ventilators classified by cycling mechanism?
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Electronically timed cycle ventilator
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In this type of ventilator, a pneumatic source is squeezing bellows and emptying contents in the bellows into the patient's breathing circuit
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Pneumatic driven double circuit ventilators
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What drives a piston to compress gas in a piston driven ventilator?
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Electric motor is pushing a piston which is then used to send gases to the patient
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What type of ventilator is a piston driven ventilator (how many circuits)?
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Single-circuit because there is no driving gas
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What is unique about using the mechanical ventilator (reservoir bag) on a piston-driven ventilator?
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Reservoir bag will inflate and deflate during mechanical ventilation - fresh gas decoupling
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What are some of the advantages of the piston ventilator?
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-Accuracy in TV -Preserves cylinder O2 -Quiet -No PEEP
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How is the piston ventilator so accurate with VT?
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Due to leak and compliance compensation and fresh gas flow decoupling
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How does a piston ventilator preserve cylinder O2?
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Bellow ventilators used oxygen to drive the bellows, piston ventilators do not
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What are the differences between bellow ventilators and piston ventilator regarding intrinsic PEEP?
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Bellows circuit pneumatic ventilator provides an intrinsic 2-4 cmH2O of PEEP, piston ventilators do not
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What are some of the disadvantages of the piston ventilator?
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-Doesn't work well with non-rebreathing circuits (Mapleson circuit) -Potential for negative inspiratory pressure -Dilution of patient's inspired gases with room air -Loss of visual cues (can't see bellows and can't see the patient take a larger breath) -Quiet
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What ventilation modes do modern anesthesia ventilators have?
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-One or more (pressure control, volume control)
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What is the most common ventilator mode (All ventilators have this mode)?
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Volume Control Ventilation (VCV)
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How does a VCV deliver a breath? -What stops this breath?
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Preset TV delivered at a constant flow, inspiration will be terminated when tidal volume is reached or when pressure becomes too high - 60-100 cmH2O (this can be an issue for patient's that can't ventilate without a high pressure)
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What parameters does the provider set on a VCV?
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-VT, MV, RR
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What is the pulmonary inspiratory pressure (PIP) on a VCV? -When will it rise?
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-It is uncontrolled -PIP will rise when our lung compliance decreases or when our airway resistance increases
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What is the relationship between VCV and patient effort? -What about the flow rate?
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-Independent of patient effort (continuous mandatory ventilation) -Flow rate fixed
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What are the settings for a volume control ventilator? -VT -RR -I:E -PEEP
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-VT 5-7 mL/kg -RR 6-12 breaths per minute (bpm) - adjust based on end-tidal CO2 -I:E (Inspiratory:Expiratory time) = 1:2 (Might adjust to 1:3-4 for COPD patients) -PEEP 0 cm H2O to start - Can add if you have trouble ventilating patients
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How does PCV deliver a breath? -How is the inspiratory pressure set?
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-Allows inspired volume to vary so we can limit our peak inspiratory pressures -High initial flow early in the respiration to reach a set pressure, then less later to maintain pressure. This helps us reach our tidal volumes -Provider will set inspiratory pressure
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What would we adjust if we were unable to achieve our goal VT with a PCV? -What do we adjust the RR to?
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-If we are unable to achieve our goal VT, we increase our inspiratory time -Adjust the RR for ETCO2 32 - 36 mmHg
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What are some indications for PCV?
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-High PIP and/or low compliance -Excessive leaks
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When might a patient have a high pulmonary inspiratory pressure and/or low compliance?
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-Pregnancy or obesity -Laparoscopic surgery (pneumoperitoneum) or one lung ventilation (i.e. thoracotomy) -Positions: Trendelenburg and or Prone -ARDS
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When are leaks common (indicating the use of a PCV)
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Leaks are common with LMA's and with uncuffed ETT used in pediatrics
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What are typical settings for pressure control ventilation? -Pressure -RR -I:E -PEEP
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-Pressure limit = 20 cm H2O -RR = 6 - 12 -I:E = 1:2 -Start with PEEP of 0 cmH2O, might have to increase to 5 cmH2O
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What is fresh gas decoupling? -When is the reservoir inflated and deflated? -What ventilators use this feature?
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-Tidal volume used to be the sum of the tidal volume and the flow rate -Fresh gas decoupling: One-way valve diverts FGF to breathing bag during inspiration -Used with piston ventilators -Reservoir will inflate with inspiration (valve closed) and deflate with expiration (valve open)
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What is fresh gas compensation? -How long does it take to work?
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Sensors detect changes in FGF and adjust TV to match that set by anesthetist (can take several breaths to detect these changes)
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Why was the pressure-controlled ventilation with volume guarantee mode created? -How does it work?
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To address problem of VT varying with compliance changes -Provider sets same parameters set as with PCV with addition of TV and the ventilator uses lowest possible pressure. It determines compliance and adjusts pressure to supply the programmed VT
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How does Synchronized Intermittent Mandatory Ventilation (SIMV) work? -What parameters does the provider set? -When is this mode useful?
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-Detects inspiratory effort and synchronizes the mechanical breath with the patient's breathing (mechanical ventilation may be irregular) -Preset volume or pressure and rate while allowing spontaneous breathing. Provider also sets minimum respiratory rate to take over if pt. is hypoventilating -Useful for emergence
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How does pressure support ventilation (PSV) work? -What ability must the patient have? -What parameters does the provider set? -When is this mode useful?
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-Senses inspiratory effort and applies positive pressure for the patient initiated breath (respiratory rate is 0) -Patient must be breathing spontaneously -Set trigger sensitivity and inspiratory pressure -Excellent for use of the LMA or when you have a spontaneously breathing patient
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What is the most common ventilator?
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Bellows ventilator - basic pneumatic ventilator
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What do the bellows serve as an interface between in a basic pneumatic ventilator?
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Interface between breathing system and ventilator driving gas
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In a pneumatic ventilator: -Where are the bellows housed? -What is the inside of the bellows connected to?
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-Housed in a chamber -Inside of the bellows is connected to the breathing circuit
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How many circuits are in a pneumatic ventilator?
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-Double-circuit - Gas drive circuit pushing the bellows and a patient circuit hooked up to the breathing system
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What is the function of the spill valve? -What about the exhaust valve? -How do they work together?
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-Spill valve: Vents excess gases to the scavenging system -Exhaust valve: Lets the driving gases out -They close to allow pressurization of the chamber
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Where is the spill valve located?
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Inside the bellows
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When do the bellows expand? -Where does the extra air go?
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-Bellows expand during exhalation -Driving gas vents to the atmosphere via exhaust valve (pure O2 or air, not anesthetic gas) -After bellows expands completely, excess gases vents through spill valve into scavenger system (Spill valve does not open until the bellows are completely expanded)
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What are factors that can affect the delivered tidal volume?
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-Fresh Gas Flow - Fresh gas compensation on newer machines -Compliance and Compression Volumes -Leaks
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What is the driving gas volume equal to in a bellows ventilator? Does this mean the VT doesn't change?
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Driving gas volume = VT in a bellows ventilator. However, pressure in breathing circuit can vary between breaths, causing changes in the VT
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What gases are used as driving gas in a pneumatically powered ventilator?
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-Sometimes only O2, sometimes air and O2
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How is the driving gas supply provided? -What does the standard specify for pressure? -What safety feature does this system use for gas connections?
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-Pneumatically powered (electronically controlled) -Standard specifies a range of 55 psig +20% and -25% -Uses the Diameter Index Safety System (DISS)
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Explain the Venturi Bernoulli Principle -What is the purpose of using this principle in pneumatic ventilators?
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-Bernoulli: As the gas flow meets a restriction, its lateral pressure drops -Helps conserve O2
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What do the controls of the anesthesia machine do? -What type of controls can they be?
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-Regulate flow, volume, timing and pressure of the driving gas -Pneumatic: Uses pressure changes to initiate changes in the respiratory cycle OR -Electronic: Most newer ventilators
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What are the types of pressure alarms on anesthesia ventilators? -What does the standard mandate?
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-High priority, Medium priority, Low priority -Standard mandates alarm for high pressure and low pressure
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Who can adjust the high pressure alarm? -What is the default setting?
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-The provider -Default is set at 50 cmH2O
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What does the low pressure alarm indicate?
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Low pressure alarm indicates that pressure in the breathing circuit has not reached a minimum valve necessary to deliver our ventilation within a certain time period
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What are the two ways that the pressure-limiting mechanism can work? -What does the standard mandate about this component?
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-Maximum pressure is reached and holds pressure until exhalation begins -Terminates pressure when the pressure limit is reached -Standard mandates this to be user adjustable
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What are the risks of setting the pressure-limiting mechanism too low?
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If the limit is too low you risk insufficient pressure for ventilation
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What are the risks of setting the pressure-limiting mechanism too high? -How do you prevent this?
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-If the limit is too high you risk barotrauma -Set the high limit 10 cmH2O above the PIP to avoid barotrauma
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What is the function of the safety relief valve? -Who sets this? At what pressure?
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-Limits pressure of driving gas in bellows -Preset by manufacturer 65-80 cmH2O
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Are the bellows assembly attached or separate from the ventilator?
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May be either
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How are the bellows classified?
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-Bellows are classified according to the direction the bellows move during exhalation -Ascending bellows: The bellows expand (rise) during expiration -Descending bellows: The bellows expand (rise) during inspiration
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Which part of the ventilator physically separates the driving gas circuit from the patient circuit (double-circuit)? -Which is inside, which is outside?
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-Bellows -Patient circuit is inside the bellows -Driving gas outside the bellows
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How are bellows classified? -Which is which?
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According to which way they move during exhalation -Descending Bellows: Inspiration: Upward, Weighted negative pressure in breathing circuit during expiration to bring bellows down
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What are some other names for ascending and descending bellows?
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-Ascending: Standing, upright -Descending: Hanging, inverted
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What happens during a disconnect with descending bellows? -What feature do newer ventilators have regarding this?
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-Continues to function with disconnect by drawing in room air at the site of the disconnect (Ascending bellows won't do this) -Newer hanging bellow ventilators use software to alarm appropriately with disconnect
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What happens during a disconnect with ascending bellows? -What does this indicate?
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Safer - Bellows will not fill with a disconnect
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What is the pressure with ascending bellows? -Why?
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-Pressure always positive -2-4 cmH2O of PEEP is due to the weight of the spill valve prevents gases within the bellows from escaping into the scavenging system during expiration until the bellows have reached full excursion
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What are the components of the bellows assembly?
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-Housing or canister surrounds the bellows allowing observation -Scale on canister = rough estimate of TV (do not use)
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This part of the ventilator communicates with bellows housing and is not in patient circuit (part of driving gas circuit)
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Exhaust valve
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In what position is the exhaust valve in at various points of respiration?
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-Closed during inspiration - Allows driving gas to build up pressure & compress bellows -Opens during exhalation - To vent driving gas to atmosphere
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What happens if the exhaust valve is open during inspiration?
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You cannot pressurize the driving circuit, the bellows will not decompress
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What sizes are the patient gas port, exhaust port, and drive gas port?
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-Patient gas port = 22 mm -Exhaust port = 30 mm -Drive gas port = 17 mm
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In what position is the spill valve in during inspiration? -In what position is the spill valve in during expiration?
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-Closed during inspiratory phase -Closed during expiratory phase until bellows are fully expanded (probable exam question)
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This part of the ventilator vents excess respired gases to be ventilated into the scavenging system during exhalation
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Spill valve
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Which part of the ventilator is basically the APL valve while mechanically ventilating?
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Spill valve
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What is the purpose of the ventilator hose connection? -What might it contain? -What does the standard require about the ventilator hose connection?
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-Connects ventilator to the breathing system -May contain a filter (not required) -Standard requires the fitting connecting the ventilator to the breathing system be a 22 mm male fitting (different from scavenging system)
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How will ventilators allow you to program the tidal volume?
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Most ventilators allow direct setting, some will require minute ventilation and figure VT from there
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How will ventilators allow you to program the minute volume? -What does the standard require regarding minute volume?
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-May be set directly or indirectly as a product of tidal volume and respiratory rate -Standard requires volume must be available to operator and be accurate to +/- 15%
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How will ventilators allow you to program the frequency? -What does the standard require regarding frequency?
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-May be set directly or indirectly by varying the inspiratory time and expiratory pause. -Standard says it must be accurate to within one breath per minute or 10% of the set value, which ever is smaller
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How will ventilators allow you to program the I:E ratio?
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-May be determined directly or indirectly by setting other controls
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What must inspiratory and expiratory time be sufficient for? -What is the usual inspiratory time?
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-Sufficient inspiratory time entire tidal volume to be delivered, sufficient expiratory time for full exhalation -Inspiratory time is usually set at 1
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How will ventilators allow you to program the inspiratory flow rate? -What will too high or low flows result in?
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-May be set directly, or indirectly by setting the minute volume, respiratory rate, and I:E ratio -Too low flow prevents a complete excursion of the bellows -Too high flow may be too fast for the needed tidal volume
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What is the purpose of the inspiratory pressure limit? -When might this limit your tidal volume?
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-Limits pressure during inspiratory phase -May limit your VT, especially in obese patient or patient with compliance issues
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Type of Ventilator -Time-cycled -Can manually set VT, RR, I:E ratio, PEEP, inspiratory pause -SIMV on either volume or pressure mode -Computer will give recommendation for VT based on height and weight
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GE ADU (Anesthesia Delivery Unit)
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Type of Ventilator TV changes to compensate for adjustments in fresh gas flow, and breathing circuit compliance losses through the D-Lite sensor (flow sensors detect compliance issues)
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GE ADU (Anesthesia Delivery Unit)
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How do you use the PCV mode on the ADU ventilator?
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-Set pressure above PEEP and set inspiratory rise time -Tidal volume and inspiratory time determined by rise time and set pressure
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Type of Ventilator -Time-cycled -TV dialed directly -Ascending bellows -Several reported hazardous malfunctions (i.e., elevated airway pressures, etc.)
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Dräger AV-E Ventilator
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List the volume controlled ventilators (VCV)
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-Dräger AV 2+ -Ohmeda 7000 -Ohmeda 7800 series
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List the combination VCV/PCV ventilators
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-GE ADU (Anesthesia Delivery Unit) -Dräger Divan -Dräger Fabius GS -Dräger Apollo -TurboVent 2 (Perseus) -Ohmeda 7900 "Smartvent"
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List the piston ventilators
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-Dräger Divan -Dräger Fabius GS -Dräger Apollo
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List the pneumatically controlled ventilators
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-GE ADU (Anesthesia Delivery Unit) -Dräger AV 2+ -Ohmeda 7000 -Ohmeda 7800 series -Ohmeda 7900 "Smartvent"
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What is the main Turbine ventilator?
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-TurboVent 2 (Perseus)
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What type of ventilators have fresh gas decoupling?
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Only piston ventilators
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-Successor to the AV2 and AVE -Ascending bellows -Dial controls your tidal volume, turn it to increase/decrease bellows -20 minute battery backup
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Dräger AV 2+
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-Dräger Narkomed 6000/6400 machine -Piston drive, can't see the piston -SIMV, PSV -Warms breathing gases -Compensation for breathing system compliance
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Dräger Divan
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-Piston is located on left side with window to view piston -Electronically controlled
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Dräger Fabius GS
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-Electronically controlled -Automated checkout procedure -SIMV-Vol, SIMV-P, PSV
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Dräger Apollo
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-Electronically driven and controlled -Works without compressed gas -Inspiratory flow to 180 L/min (much higher than most -PEEP to 35 cm H2O -Breathing bag moves during mechanical ventilation -Turbine draws inspiratory volume from bag and FGF
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TurboVent 2 (Perseus)
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-Bellows (ascending) assembly -Control module -MV, RR, and I:E ratio control (not interactive) - If you increase RR without changing MV you will decrease VT -Uses oxygen only - using air or N2O will damage the ventilator -Very sick patients with low compliance may not be effectively ventilated because pressure limited to 65 cm H2O -Sigh control can be left on
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Ohmeda 7000
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Ohmeda 7800 Series -_____ can be a stand-alone ventilator -_____ & _____ have separate control module and bellow assembly. -_____ has a blank screen unless a control is altered or pressed.
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-7800 -7810 & 7850 -7850
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-Same bellows assembly as 7000 and 7800 series -Screen is integral contrast enhancement type (ICE) -First "modern" anesthesia ventilator
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Ohmeda 7900 "Smartvent"
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How can hypoventilation happen?
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-Ventilator dysfunction -Ventilator turned off - happens with "tube & turn cases) -Circuit disconnect -Obstruction -PEEP - Increasing PEEP might decrease VT because of high pressure
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What is the most common cause of critical incidents?
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Circuit disconnect
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What are general hazards of ventilators?
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-Hypoventilation -Hyperventilation -Hyperoxia -Excessive Airway Pressure -Negative pressure during expiration (hanging bellows) -Alarm fatigue
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What should you keep in mind about excessive airway pressure?
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-It requires immediate attention
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What are advantages of ventilators in anesthesia?
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-Allows other tasks/eliminates fatigue -Accurate regular respiratory rate -Simple in design
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What are disadvantages of ventilators in anesthesia?
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-Loss of contact between provider and patient (don't notice compliance issues) -False sense of security? -Older ventilators can lack appropriate alarms and monitors -Many cannot develop high enough flows, pressures or PEEP to ventilate critically ill patients. (That's changing somewhat) -Difficulty cleaning -Noisy
