Week 9 Ventilators and Airway Monitors Flashcards

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1
Q

Describe possible issues with piston ventilators.

A
  • refill even if a circuit disconnection occurs
  • if a circuit leak is present, piston may entrain RA through the leak → diluting oxygen and anesthetic agent
    • associated risks
      • hypoxemia
      • awareness
    • Alarm should alert the operator
  • positive pressure relief valve prevents excessively high breathing circuit pressure (60 to 80 cm H2O)
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2
Q

Distinguish ICU vents and anesthesia vents.

A
  • ICU ventilators are more powerful allowing for greater inspiratory pressures and tidal volumes
  • CO2 absorber - anesthesia vents
  • ICU ventilators support more modes of ventilation
    • Changing!!
  • Gas supplied by the ICU ventilator directly ventilates the patient
  • Anesthesia driving gas never reaches the patient
    • 100% O2 in old machines
    • Air/100% O2 in newer models
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3
Q

Describe Pressure Support Ventilation as a mode of ventilation.

A
  • aid in normal breathing with a predetermined level of positive airway pressure
  • pt spontaneously breathing
  • PSV senses patient inspiratory effort (volume or flow) and delivers pressure support
  • results in larger TV than the patient would produce on their own
  • PSV is useful to support MV and control arterial CO2 for spontaneously breathing patients during maintenance and emergence
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4
Q

How do you calculate the I : E ratio?

A
  • Time spent in inspiration
  • TI = TV / Flow rate
    • TV = IBW * 5-7 ml/kg = ____ mL
    • Flow rate = 4 - 6 X minute ventilation
      • MV = TV X RR
      • X 60 seconds
  • TE = (60 seconds / RR) - TI
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5
Q

What is the formula for oxygen delivery?

A

Oxygen delivery = CO x O2 content

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6
Q

Distinguish between ascending and descending bellows.

A
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7
Q

Bellows are classified by direction of bellows movement during _________.

A

EXPIRATION

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8
Q

How are we going to make sure that our ventilator settings are okay and that we are ventilating adequately?

A

PEtCO2

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9
Q

Discuss volume as a parameter used to describe ventilation.

A
  • measure of the tidal volume delivered by the ventilator to the patient
  • volume of gas patient breaths
  • expressed in mls
  • expressed in Ls for minute volume
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10
Q

Describe the disadvantage of the descending bellows type ventilator.

A

These bellows will continue regular upward and downward movement despite patient disconnection: the drive gas pushes the bellows upward during the inspiratory phase, and during the expiratory phase the bellows “fills” with entrained room air instead of the patient’s exhaled gas, because of the weighted bellows. The pressure monitor and the volume monitor may be fooled even if disconnection is complete.

**An essential safety feature of any anesthesia workstation that uses a descending bellows is an integrated CO2 apnea alarm that cannot be disabled while the ventilator is in use.**

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11
Q

Each time you increase FiO2 by _____ you increase PaO2 by _______.

A

10%; ~50 mmHg

  • PaO2 FiO2
  • 100 21%
  • 150 30%
  • 200 40%
  • 250 50%
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12
Q

Discuss time as a paramter used to describe ventilation.

A
  • divided into insp and exp periods
  • expressed in seconds OR by relation of insp time to exp time expressed as I:E ratio
  • used to define the number of respiratory cycles within a given time period
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13
Q

If ventilation is in adequate and we want to increase minute ventilation, in general, will we first increase RR or TV?

(think of Dr. E’s pearl in anesthesia, practical purposes)

A
  • Tidal volume first
    • recruit alveoli, not being ventilated as well as when patient is awake with negative pressure ventialtion
    • however, must consider pressures as well
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14
Q

Describe features of a piston ventilator.

A
  • use computer controlled stepper motor vs drive gas
    • analagous to pushing plunger of syringe
  • single circuit
  • less gas used
    • great for remote locations
  • more accurate TV delievery tied to piston movement
  • **However, feedback mechanisms that help maintain stable tidal volume delivery are becoming increasingly more common**
    • circuit compliance compensation
    • use of inspired tidal volume measurement
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15
Q

Discuss flow rate as a parameter used to describe ventilation.

A
  • 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

FR = 4 - 6 X Minute Volume

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16
Q

Describe the mechanism of the Maquest FLOW-i Anesthesia System with volume reflector.

A
  • newer vents, not commonly in use
  • uses a “volume reflector”
    • functional and “in circuit” during all modes of ventilation
    • gases are mixing
      • exhaled gases
      • FGF
  • breathing bag not in play during mech ventilation
  • PEEP/APL valve closed during inspiration, open during expiration for scavenging
  • during expiration, lots of CO2 and less oxygen in the volume reflector
  • during inspiration, gas from volume reflector THEN goes through CO2 absorber and mixes with FG to go to patient
  • at the end of exhalation, the volume reflector is filled at its proximal end (near the patient) with exhaled gas and is filled distally with a mixture of exhaled gases and reflector gas
  • during inspiration, reflector gas module pushes the exhaled gas back out of the volume reflector, much like a piston, through the CO2 absorber, to the patient. Fresh gas combines with the volume reflector outflow to maintain the desired oxygen and anesthetic concentration
  • The fresh gas modules and the reflector gas module work together in a coordinated manner to control gas flow and pressure in the breathing circuit so that operator determined ventilation parameters are maintained
17
Q

Discuss pressure as a parameter used to describe ventilation.

A
  • impedance to gas flow rate
  • impedance encountered in
    • breathing circuit
    • patients airways and lungs
  • amount of backpressure generated as a result of
    • airway resistance
      • ETT
      • bronchi
      • bronchioles
      • alveoli
    • lung-thorax compliance
  • expressed in cm H2O, mmHg, kPa
18
Q

Describe the flow of gas through the piston ventilator during expiration.

A
  • FIRST STEP OF EXHALATION
  • patient exhales into breathing bag
  • fresh gas continues to flow in retrograde fashion
  • SECOND STEP OF EXHALATION
  • ventilator returns to its starting position, drawing in gas stored within the breathing bag and fresh gas from the gas supply system
  • once the piston reaches the bottom of its stroke, fresh gas flow reverses course and flows in retrograde fashin toward the breathign bag and the absorber
  • excess gas vents through the exhaust valve to the scavenger
19
Q

Discuss possible issues with a bellows ventilator.

A
  • leaks
    • improper seating
  • hole in the bellows
    • hyperinflation of the lungs
      • think drive gas going to patient lungs
    • O2 concentration can change
  • ventilator relief valve problems
    • hypoventilation
      • gas goes to scavenger rather than drive
      • caused by disconnection, ruptured valve, or other damage
      • could be noted with PEtCO2
    • stuck valve in closed position
      • additional PEEP and excess pressure
      • excess suction from scavenging can also cause the valve to close and cause increased pressure
      • could be noted with pressure monitors/alarms
20
Q

Parameters used to describe ventilation.

A
  • time
  • volume
  • pressure
  • flow rate
21
Q

List 4 monitors discussed.

A
  • ETCO2 monitor/capnography
    • best for revealing disconnects
    • adequate ventilation?
  • oxygen analyzers
    • most important monitor on the machine
    • calibrate at 21%
  • respirometer
    • vent settings
    • PAP monitors
  • VIGILANCE
    • sweep check
22
Q

Many vents can operate in VC or PC modes. Distinguish between the two.

A
  • Volume controlled
    • terminates inspiration when a preselected TV is delivered
    • most adult vents are V cycled but have a second limin in inspiratory pressure to guad against barotrauma
    • a percentage of TV is always lost to the _compliance of the system (not patient)_
      • usually about 4 - 5 cm H2O.
  • Pressure controlled
    • cycle into expiratory phase when airway pressure reaches a predetermined level.
    • TV and inspiratory time vary
    • used in situations where pressures can be high
    • useful in neonates/premies

**All vents are under electric control**

23
Q

Explain the flow of gas through a piston ventilator during inspiration.

A
  • The PEEP/maximum pressure (Pmax) valve is held closed
  • The pressure in the breathing circuit that is generated by the ventilator closes the fresh gas decoupling valve
  • This directs gas flow tward the breathign bag during inspiration so it does not interfere with TV accuracy
  • Excess fresh gas flows past the open APL bypass valve, though the exhaust valve, and to the scavenger
  • **Note how the breathing bag is integral to cirucit function during mechanical ventilation**
24
Q

Describe CPAP as a mode of ventilation.

A
  • CONTINUOUS POSITIVE AIRWAY PRESSURE
  • positive pressure is maintained during both inspiration and expiration
  • can be provided with mask
    • CAUTION: if pressures > 15 cm H2O, can cause regurgitation and aspiration
25
Q

Describe the mechanism of expiration in the bellow ventilator.

A
  • the drive gas exits the bellows chamber
    • pressure within bellows and the pilot drop to zero causing the ventilator relief valve (pop off valve) to open
  • Exhaled pt gas fills the bellows before any scavenging occurs because the valve ball produces a 2 - 3 cm H2O back pressure
    • scavenging occurs ONLY when the bellows are filled completely
  • the relief/pop off valve is ONLY open during expiration, and any scavenging occurs at this point
26
Q

How much O2 do we give? Think of hypoventilation. What is the formula?

A
  • Factors to consider:
    • hypoventilation
      • reduces PaO2 except when the subject breathes enriched O2 mixture
      • from sedation
      • switching from NPV to PPV
        • derecruiting alveoli
    • PaO2 = PIO2 - PaCO2 / R + F
      • R = extraction ratio (0.8) for CO2
      • F = correction factor (small and negligble
      • THUS
        • PaO2 = PIO2 - PaCO2/R
27
Q

What is the breathing gas?

A

FGF + Anesthetic + what the patient exhales

28
Q

List 6 ventilator alarms discussed.

A
  • low pressure alarm (disconnect alarm)
    • detected by a drop in peak circuit pressure
    • circuit disconnect
    • bellows leak
  • sub atmospheric pressure alarm
    • pressure of < or = -10 cm H2O
    • pt trying to breathe against ventilator
  • sustained/continuing pressure alarm
    • 15 cm H2O for more than 10 seconds
  • high peak airway pressure alarm
    • detects excess pressure in system
    • activated at 60 cm H2O OR set by practitioner
  • low oxygen supply alarm
  • ventilator setting alarm
    • vent’s inability to deliver the desired MV set
      • older machines
29
Q

Describe the bellows ventilator and the mechanism during inspiration.

A
  • pneumatically driven
  • bellows separate the driving gas from the pt gas circuit
    • double circuit
    • like practitioner squeezing the reservoir bag
  • bellows serves as the reservoir for pt breathing gases
  • driving force is the pressurized gas that flows into the bellows housing
  • during inspiration phase, the driving gas enters the chamber and increases pressure
  • The above increase in pressure casuses 2 things to occur
    • the ventilator relief valve closes (pop off valve)
      • so no gas can escape into the scavenger
    • the bellows are then compressed and the gases in the bellows are delivered to the patient
      • (analagous to you squeezing the bag)
30
Q

Describe high frequency ventilation as a mode of ventilation.

A
  • low tidal volumes, less than dead space
  • high rate (60-300 bpm)
  • Typical settings
    • 100-200 bpm
    • IT 33%
    • Drive pressure: 15-30 psi
  • GOAL
    • maintain pulmonary gas exchange at lower mean airway pressures
    • Used in ESWL
31
Q

What is the respirometer and where is it located? What sensors, monitors and alarms are included?

A
  • TV sensor
  • in expiratory limb
  • gas flow converted to electrical pulses
  • exhaled Vt expect to measure
    • Vt = Vt set on vent + Vt FGF - Vt lost in system
  • Exhaled volume monitor
    • activated automatically once breaths are sensed and always active during mechanical ventilation
  • Apnea
    • If sufficient breath, based on TV setting, not achieved within 30 seconds
  • low minute volume
32
Q

Discuss ventilator settings: TV, RR, Flow Rate, and I:E ratio.

A
  • Tidal Volume
    • 5-7 ml/kg (older vents up to 10 ml/kg)
    • **use IBW**
  • RR
    • ~ 8-12/min
  • Flow rate (machine doing, not me)
    • 4 - 6 X minute ventilation
    • MV = TV X RR
  • I : E ratio
    • **physiologic is 1 : 2**
33
Q

Discuss the options for drive gas and the advantages/disadvantages of each.

A
  • Either oxygen or air
  • Advantage of O2
    • if there is a leak it prevents hypoxic mixture from being administered to patient
  • Disadvantage of O2
    • can deplete oxygen quickly if not hooked up to pipeline
  • some machines can entrain room air
    • reduces need for O2
    • ideal in austere conditions
34
Q

What is the formula for oxygen content?

A

(hgb x %sat x 1.39 ml O2) + (PaO2 x .0031 ml O2)

  • 1 gram of pure Hb combines with 1.39 ml O2
  • For each mmHg of PO2 there is .0031 ml O2/100 ml blood
    • normal arterial blood with a PaO2 of 100 mmHg contains 0.3 ml O2/100 ml