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Intro To Anesthesia > Ventilators and Airway monitors > Flashcards

Flashcards in Ventilators and Airway monitors Deck (47):


  • In expiratory limb
  • exhaled TV sensor
    • activated automatically once breaths are sensed and always active during mechanical ventilation
  • gas flow converted to electrical pulses
  • apnea- if sufficient breath (based on TV setting) not achieved within 30 seconds
  • low minute volume


Expiration phase- bellows ventilator

  • drive gas exits the bellows chamber via ventilator pop off valve and pressure in chamber drops to zero
  • exhaled pt gas fills the bellows before any scavenging occurs 
    • b/c valve ball produces a 2-3 cm H2O back pressure.
    • relief (pop off) valve is ONLY open during expiration when all scavenging takes place



  • Pressure support ventilation
    • aid in normal breathing with predetermined level of positive pressure
    • pt spontaneously breathing
    • senses pt insp effort and gives pressure support
    • results in larger TV than pt would produce independently
    • useful to support MV and control arterial CO2 for spontaneously breathing patients during maintenance or emergence


Pressure controlled

  • cuts off inspiration when pressure meets the predetermined level.  TV and inspiratory time vary


possible issues with bellows

  1. leaks, improper seating
  2. hole in bellows
    1. hyperinflation of the lungs
    2. O2 concentration can change
  3. ventilator relief valve problems
    1. hypoventilation- gas goes to scavenger rather than drive
    2. caused by- disconnection, ruptured valve, or other damage
    3. valve stuck in closed position- additional peep and excess pressure
    4. excess suction from scavenge can also cause the valve to remain closed.


Ventilator settings

  • TV: 5-6 ml/kg (ideal weight)
  • RR: 8-12
  • Flow rate: about 4-6 x minute ventilation
  • I:E ratio: physiologic is 1:2
    • Time Inspired= TV/ Flow rate


drive gas

  • either air or oxygen
    • using oxygen depletes supply quickly because so much goes to scavenge.
  • some machines can entrain air, reducing the need for oxygen
    • used in austere conditions (military)


Ventilation VOLUME

  • measure of the tidal volume delivered by ventilator to patient
  • volume of gas pt breaths
  • expressed in mls
    • Liters for minute volume



ICU vents Vs anesthesia vents

  • ICU
    • more powerful- greather insp pressures and tidal volumes
    • more modes of ventilation
    • gas supplied by the ICU ventilator directly ventilates the patient
  • Anesthesia
    • CO2 absorber
    • driving gas never reaches the patient
      • 100% O2 in older machines
      • air/100% O2 in newer models


To Select Ventilation mode:


  1. Push the Ventilator key
  2. Review the settings for the new mode.
  3. Select Mode
  4. Select desired mode (mode is changed immediately upon selection)

*Ventilator is electonically controlled and pneumatically driven.



possible issues with pistons

  1. refill even if a circuit disconnection occurs
  2. if a circuit leak is present, piston ventilators may entrain RA through the leak, diluting O2 and anesthetic
  3. risk of hypoxemia and awareness
    1. an alarm will sound
  4. a positive-pressure relief valve on the ventilator prevents excessively high breathing circuit pressure (60-80 cm H2O)


TI equation

TI = TV/ Flow rate


feedback mechanisms for Pneumatic bellows ventilators

  • help administer more stable tidal volume
  • circuit compliance compensation and measure tidal volume as a feedback signal.




MV = TV x RR



  1. ETCO2- capnography- best for revealing disconnect.
  2. Oxygen analyzer- most important monitor on the machine.  Calibrate at 21%
  3. Respirometer- measures exhaled volumes
  4. PAP monitors- peak airway pressure
  5. vigilence is the best monitor


For each mmHg of PO2 ...

...there is .0031 ml O2/100ml of blood

*normal arterial blood with a PO2 of 100 mmhg contains 0.3 ml of O2/100 ml


Maquet FLOW-i Anesthesia System With Volume Reflector

  • uses "volume reflector"
    • volume reflector is functional and "in circuit" during all modes
  • expired gas gets "balanced" by Reflector gas


TE equation

TE = total time for each breath - TI

Total time for each breath:

60 sec/ RR (12 bpm) = 5 sec/breath



Ventilation TIME

  • divided into inspiratory and expiratory
  • expressed in seconds
  • OR by relation of insp to exp.  I:E ratio
  • used to define the number of respiratory cycles within a given time period.


modes of ventilation

  1. CV
  2. IMV
  3. SIMV
  4. AC
  5. PSV
  6. HFV
  7. PCV
  8. CPAP


Ventilator relief valve

aka pop-off valve

  • closes during inspiration so that pressure can be maintained and can push down the bellows.
  • opens during expiration so driving gases can leave casing and go to scavenge and make room for bellows to expand.



  • SIMV- like IMV but synched with pt's effort

    • Pt breaths spontaneously and at interval the breath is supported by the machine


one gram of pure hemoglobin...

...can combine with 1.39 ml of O2


Parameters used to describe ventilation

  1. time
  2. volume
  3. pressure
  4. flow rate


Ventilation PRESSURE

  • impedence to gas flow rate
  • impedance encountered in:
    • breathing circuit
    • pts airway and lungs
  • amount of backpressure generated as a result of:
    • airway resistance
    • lung-thorax compliance
  • expressed in cmH2O, mmHg, or kPa


How much O2 do we give?

PaO2 = (PIO2 - PaCO2)/R

R = extraction ratio (0.8)

** Hypoventilation reduces PaO2 except when the subject breathes enriched O2 mixture


ventilation FLOW RATE

  • rate at which the gas volume is delivered to the pt
    • from the pt connection of the breathing system to the patient
  • refers to the volume change/time
  • expressed in L/sec or L/min


Modes of ventilation newer machines

  • Patient can trigger
    • thus, "Non-controlled ventilators"
  • Synchronized intermittent mandatory ventilation (SIMV)
  • Assist control (AC)
  • Pressure support (PSV)


Increased FiO2

  • each time you increase FiO2 by 10%, you increase PaO2 by about 50 mmHg


Oxygen content equation

oxygen content = (hemoglobin x saturation x 1.4 ml O2) + (PaO2 x .0031 ml O2)



  • High frequency ventilation
    • Jet ventilator- used for lithotripsy so that the kidney stones dont move every time pt takes breath
    • low volumes, high rate, less dead space
    • typical settings 
      • BPM 100-200
      • IT 33%
      • Drive pressure 15-30 PSI
    • goal to maintain pulm gas exchange at lower mean airway pressures



Controlled ventilation



  • Almost always pneumatic
  • Ascending- bellows ascends during expiratory phase
  • Descending- bellows descends during expiratory phase


Pneumatically driven bellows ventilator

  • bellows separates driving gas from pt. circuit gas
    • double circuit
  • bellows serves as reservoir for pt breathing gas
    • bellows is kind of equivalent to provider squeezing bag.
  • force driving the bellows during inspiratory phase is pressurized gas. Increasing pressure causes 2 things to occur.
    • ventilator relief valve closes off so no gas can escape into scavenge
    • the bellows are then compressed and the gasses in bellows are delivered into patient.



  • Assist control
    • Intermittent positive pressure ventilation
    • pts insp effort creates a sub-baseline pressure in the inspiratory limb of circuit that triggers the vent to deliver a predetermined TV
    • if pts rate drops below a preset min, machine takes over with controlled vent mode
    • Can be pressure controlled or volume controlled


Piston Ventilators

  • use computer controlled stepper motor instead of drive gas
  • single circuit
  • less gas used-great for remote locations
  • more accurate TV delivery


Modes of Ventilation on older machines

  • Time triggered and time cycled
  • cycle to the exp phase once a predetermined interval elapses from the start of inspiration
  • TV is a product of the set insp time and insp flow rate
  • "Controller Ventilators"- has only one mode



  1.  Low pressure alarm (disconnect)- detected by a drop in peak circuit pressure
  2. sub atmospheric pressure alarm- pressure of < or = -10 cm H2O
  3. Sustained/continuing pressure alarm- 15 cm H2O for more than 10 secs
    1. Pt in bag mode and you havent opened relief valve
  4. High peak airway pressure alarm- detects excess pressure in system about 60 cm H2
  5. Low O2 supply alarm
  6. ventilator setting alarm- vent's inability to deliver the 


Expiratory phase- piston ventilator

  • Step 1: pt exhales into the breathing bag. FGF flows backward toward bag and CO2 scrubber.
  • Step 2: Piston returns to starting position, pulling gas from breathing bag and FGF.  
    • once piston reaches bottom of stroke, FGF flows backward toward breathing bag and absorber again. 
  • **gas flows through CO2 scrubber during exhalation for this machine


Inspiratory phase- bellows

  • driving gas enters the bellows chamber, increasing pressure and thereby compressing the bellows which delivers the gas to the patients lungs.


Classification of Ventilators

  • Classified according to the type of reservoir the ventilator has
    • Bellows
    • Piston
    • Volume
  • And how it delivers the gas (drive mechanism)
    • pneumatic
    • mechanical


Inspiratory phase- Piston ventilator

  • during inspiration the PEEP valve is held closed.  
  • The pressure in the breathing circuit that is generated by the ventilator closes the fresh gas decoupling valve
    • this directs the FGF toward the breathing bag during inspiration so it does not interfere with TV accuracy
  • excess gas flows past the APL valve, through the exhaust check valve, and to the scavenger
  • ***reservoir bag is integral to funtion during mechanical ventilation.



  • IMV- intermittent mandatory volume
    • pt breaths spontaneously while the vent delivers a preset TV at a predetermined interval through a parallel vent circuit.  Used for weaning.
    • fixed rate, not synched with patient


Volume controlled

  • cuts off inspiration when preselected TV is delivered. 
    • most have a second limit for inspiration and pressure limit to prevent barotrauma.
    • a percentage of TV is always lost to the compliance of the system (4-5cc/cmH2O)



  • Pressure control ventilation
  • pt or time triggered pressure limited, support
  • gas flow decreases as airway pressure rises and ceases when airway pressure equals the set peak inflation pressure
    • TV not fixed
    • used in situations where pressures can be high
    • used in neonates/premies



  • Continuous positive airway pressure
    • positive pressure is maintained during both inspiration and expiration
    • can be provided with a mask
      • if pressure > 15 cm H2O, can cause regurgitation and aspiration


Oxygen delivery equation

Oxygen delivery = CO x O2