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Anesthesia Equipment Exam 2 > Airway Pressure, Volume, and Flow Monitoring > Flashcards

Airway Pressure, Volume, and Flow Monitoring Flashcards

1
Q

What do pressure, airflow, and volume measurements quantify?

A

Basic physiologic properties of the respiratory sytem such as resistance, compliance, and breathing as well as pulmonary physiology

  • Interpretation of these variables is essential to ventilator managment with the ultimate gola of optimizing ventilation or the process by which oxygen and CO2 are exchanged
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2
Q

Tidal Volume (mL)

A
  • based on weight
  • volume of gas entering (insp) or leaving (exp) a patient during the inspiratory or expiratory phase
    ie: VC w 70kg pt, start w 5-7mL/kg so 500 -700 TV (some staff say 10 mL/kg but lower TV w higher RR is more lung-protective)
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3
Q

Minute Volume (mL/min)

A
  • AKA Minute Ventilation
  • sum of all TVs in one minute (volume/min)
    ie: TV x RR (so TV 500 and RR 10, my MV is 500mL/min)
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4
Q

Peak Pressure (cm H2O)

A
  • maximum pressure during the inspiratory phase time
  • set in pressure control. Start w 20 or 15 w 5 of PEEP for a total of 20. Most people with 20 PP will get normal TV.
  • Peak pressure varies w VC if you have a patient end with resistance or compliance
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5
Q

Inspiratory/Expiratory Flow Rate (mL/min)

A

- P vs V control

  • rate at which gas is inspired/exhaled
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6
Q

Inspiratory/Expiratory FLow Time (sec)

A

- Insp rise time

  • period between the beginning and end of inspiration/expiration
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7
Q

Inspiratory Pause Time (sec)

A

- Increased or Decreased

  • the portion of inspiratory phase at which the lungs are held inflated at a fixed pressure or volume
  • a delay in the onset of expiration after inspiration is complete
  • Why would we want this? It helps improve gas distribution in small airways of the lungs and can measure static compliance or Pplat…
  • -* can be applied either by an inspiratory pause control on vent or by occluding expiratory port at end-expiration
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8
Q

Expiratory Pause Time (sec)

A

- I:E, change RR

  • time from the end of expiratory flow to the start of inspiratory flow
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9
Q

Inspiratory/Expiratory Phase Time (sec)

A

- I:E, change RR

  • entire time between start of inspiratory/expiratory flow to the start of expiratory/inspiratory flow
  • set by RR. Higher rate = shorter insp/exp time and vice versa
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10
Q

What setting gives you better volume for your pressure?

A
  • Pressure Control.
  • so if you hvae problems w peak pressure you can switch from volume to pressure control
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11
Q

Which setting is best for asthma patients?

A
  • PCV with its rapid delivery of decelerating flow is more efficient at overcoming the high resistance of the asthma pts lungs. The decelerating flow pattern decreaes peak pressure needed to deliver an identical volume as a square flow (volume) waveform breath.
  • distribution of ventilation should also improve as the large airways full with the initial peak flow and the smaller airways fill with the smaller flow
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12
Q

VC vs PC Graphic

A
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13
Q

PCV-VG

A
  • delivers preset tidal volume w lowest possible pressure using decelerating flow
  • 1st breath is VC visible on screen as a “square” flow waveform and “shark-fin” pressure wave form for 1st breath
  • pt’s compliance determined from this 1st breath and pressure is then established for subsequent PCV-VG breaths.
  • have characteristic decelerating flow waveform and square pressure waveform
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14
Q

PCV-VG Graphic

A
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15
Q

How to Determine I:E Ratio

A
  • If pt is breathing 20 breaths/min means total cycle time is 3 seconds (60 sec/min divided by 20 breaths/min)
  • 1 L TV delivered @ 60L/min (1L/sec) takes 1 sec to deliver, leaving 2 seconds for exhalation.
  • I:E ratio is 1:2
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16
Q

When would you want a longer expiration?

A

With obstructions because you have impaired exhaltion so you want plenty of time to exhale. You can cause air trapping, barotrauma, and pneumo ????

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17
Q

When would you want to INCREASE inspiratory time?

A
  • relisten to heathers lecture for this answer :(
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18
Q

Air trapping graphic

A
  • normally you will return to baseline if you have a normal expiratory time. If it doesn’t return to baseline you may have air trapping.
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19
Q

Inverse I:E

A
  • prolonged inspiratory phase allows recruitment of “long time-constant” alveoli
  • short expiratory phase = auto-PEEP
  • no studies have proved efficacy, reserved only w severe respiratory failure
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20
Q

Peak Pressure

A
  • max pressure during inspiratory phase
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21
Q

Plateau Pressure

A
  • resting airway pressure during inspiratory pause
  • lowering of airway pressure from the peak pressure as airway resistance is overcome and the alveoli and small airways are held inflated at a fixed volume
  • gaol is plateau pressure <30 mmH20
  • represents static compliance
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22
Q

Total Airway Resistance

A

peak pressure - plateau pressure = total airway resistance

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23
Q

Inspiratory Pause Time

A

portion of inspiratory phase at which the lungs are held inflated at a fixed pressure or volume

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24
Q

Resistance

A
  • impedence to flow
  • ratio of the change in driving pressure to the change in flow rate: R= change in pressure/change in flow
  • expressed as cmH2O/L/sec
  • in there is an increase in resistance the P needed to deliver a given TV will increase
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25
Q

How to overcome higher resistance for a given TV?

A
  • usig lower flow for longer time or higher driving pressure
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26
Q

Compliance

A

ratio of a change in volume to a change in Pressure

  • total compliance = elasticity of the lungs, thorax, abd and breathing system
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27
Q

How do muscle relaxants effect compliance?

A
  • Using muscle relaxants will increase chest wall and abdominal compliance but not lung tissue compliance
  • relaxed chest wall easier to inflate
  • in paralyzed patients, changes in compliance reflect changes in lung tissue compliance
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28
Q

What does the plateau pressure represent?

A
  • plateau pressure represents the toal respiratory system elastic recoil at end-inflation volume

static compliance = tidal volume/plateau pressure-PEEP

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29
Q

Static Compliance

A
  • refers to the P/V relationship when air is NOT moving
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30
Q

What increases static compliance?

A
  • decreases w conditions that make it difficult to inflate (obesity, fibrosis, vascular engorgement, external compression like surgeons elbow)
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31
Q

What increases static compliance?

A
  • emphysema because it destroys the lung tissue and therefore reduces elastic recoil, resulting in lung air trapping
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32
Q

Dynamic Compliance

A

refers to the P/V loop when air IS moving

  • dynamic compliance decreases w airway obstruction such as foreign bodies and bronchospasm
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33
Q

Determining Compliance vs Resistance in VC Ventilation

A
  • increase in difference between peak and plateau pressures = increase in resistance
  • increase in plateau pressure = decrease in compliance
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34
Q

Total Airway Resistance

A
  • estimated by difference between peak and plateau pressures (normally 2 to 5 cm H20)
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35
Q

What happens if there is an increase in resistance?

A
  • higher peak pressure will be necessary to produce the same flow
  • plateau pressure depends ONLY on compliance and will not be affected by resistance
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36
Q

Interpreting Pressure-Time Waveforms (visual)

A
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37
Q

High peak pressures are due to what?

A
  • increases in airway resistance
38
Q

High peak pressure with a high plateau pressure and a normal plateau to peak pressure difference indicates what?

A
  • that high peak pressures are due to compliance issues
39
Q

High Peak Pressure Alarm Visual

A
40
Q

Static Compliance Calculation

A

tidal volume / (plateau P - PEEP)

  • normal is 35 - 100
41
Q

Resistance calculation

A

peak P - plateau P

42
Q

Ways to increase compliance and decrease resistance

A
  • decrease TV (increase RR)
  • increase compliance (muscle relaxant)
  • increase respiratory time (increase I:E, decrease RR, decrease inspiratory flow time, change from VC to PC)
  • reduce resistance (pouiselles = increase ETT size, decrease density w heliox, decrease length of circuit)
  • reduce PEEP
43
Q

D-Lite Gas Sampler & Flow Sensor

A
  • measures flow via measuring pressure differenc eacross a flow resistor (capillary tube) in a tube.
  • 2 sensing tubes, one facing direction of flow (total pressure), and the other facing opposite way to measure static pressure
  • difference in pressure between total and static pressures is the dynamic pressure, which is proportional to the square of gas flow
44
Q

Dynamic Pressure

A
  • difference in pressure between total and static pressures, which is proportional to the square of gas flow
45
Q

Airway Pressure & Volume Alarms

A
  • high/low pressures = major cause of adverse incidents
  • warn providers of these conditions when set volumes are not reached or are too high
  • often turned off by providers (SAFETY ISSUE!)
  • problem w volume monitors is you will often induce a low minute volume to get a patient to breath at the end of a case
46
Q

Disconnect Alarm

A
  • ASA/AANA standard state than when using a vent there shall be a means to detect a disconnection between breathing system components in continuous use
  • low insp peak pressure alarm
  • apnea
  • loss of CO2
  • spirometry loop changes
  • smell of volatile gases
  • text states there is no such thing as a disconnect alarm… this is true! you must detect this
47
Q

Low Peak Pressure Alarm

A
  • activated when vent turned on
  • disconnect/leak in circuit
  • leaking tracheal cuff
  • malfunctioning scavenger (suction too high)
  • gas/power supply loss
  • obstruction upstream of sensor
48
Q

Negative Pressure (sub-atmospheric) Alarm

A
  • pt w deep inhalation agent against a collapsed reservoir bag or increased resistance
  • suction too high on scavenging
  • suction placed within berathing system (endobronchoscope)
49
Q

Sustained Elevated Pressure Alarm

A
  • continuous pressure monitor activates an alarm if the pressure does not fall below a certain level during part of the respiratory cycle
  • accidental 02 flush valve activation
  • obstructed limb
  • partially closed APL in spont mode
  • scavenging occlusion
  • mafunctioning PEEP
50
Q

High Pressure Alarm

A
  • activated if pressure exceeds 50-80 cmH20
  • most machines have pressure limiting valve that opens
  • airway/breathing circuit obstruction
  • 02 flush during inspiration
  • punctured pneumatic bellows
  • pt coughing/bucking/bronchospasm
51
Q

Spirometry Loops

A
  • pressure and flow volume loops provide real time info about airway and breathing circuit problems
  • can help guide interventions to optimize ventilation
52
Q

Compliance Loop (P-V)

A
  • p-v relationship reflects pulmonary and tracheal tube mechanics
  • line from zero point through end inspiration represents compliance
  • compliance is determined by dividing TV/pressure at end inspiration
  • good compliance forms an angle of 45 degrees or less
  • horizontal loop = decreased compliance
53
Q

PCV Flow-Volume Loop

A
  • varies from VC as inspiratory flow is NOT constant
  • flow rapid @ beginning of insp then decreases
  • rapid initial increase in pressure until set pressure reached
  • TV rises slowly until set pressure is reached then increases rapidly until max point
  • flat exhaltion results from residual pressure which slows exhalation
54
Q

PC vs VC Pressure Volume Loop (visual)

A
  • in PC, flow is not constant and loop is wider
  • in VC, flow is constant
55
Q

VCV Flow-Volume Loop

A
  • loop in clockwise direction, monitor displays FLOW through ventilation cycle
  • flow rate increases (down/away from machine)
  • TV is point where flow returns to 0 and loop crosses horizontal axis
  • shape of insp side depends on type of ventilation, VC/PC or spont mode
56
Q

PC vs VC Flow-Volume Loop (visual)

A
57
Q

Spontaneous Breathing Loop

A
  • flow rate during insp varies more than w mechanical ventilation
  • insp/exp mirror each other
  • TV during spont is lower than with controlled ventilation
  • flow during exhaltion is similar to VC
58
Q

Methods of Display (visual)

A
  • may be upside down where inhalation point begins at 0 and not at FRC
59
Q

PEEP loop

A
  • what is the difference between 1st and 2nd loop? PEEP!
60
Q

Another PEEP loop

A
  • produces a decrease in expiratory flow
61
Q

PV Loop, Spontaneous with CPAP

A
  • loop starts at CPAP value and moves left
  • inspiration begins w negative pressure and TV increases quickly
  • during exhalation, loop moves right, flat at first as pt breathes against CPCP
  • large internal loop indicates decreased WOB
62
Q

How can you tell on a loop if the breath is spontaneous?

A
  • when the loop goes negative (the vent cannot go into negative pressure!)
63
Q

PV Loop with intermittent mandatory ventilation (visual)

A
  • both spontaneous and vent-controlled breaths
64
Q

PV Loop w Patient-Triggered Ventilation

A
  • as pt takes breath, loop becomes positive for duration of inspiration
  • loop negative (neg pressure) until vent kicks in (positive pressure)
65
Q

PV Loop Spontaneous-Assisted Ventilation

A
  • negative pressure as pt begins to inspire
  • bag is squeezed and pressure becomes positive
  • shape of inspiratory portion depends on how the bag is squeezed
66
Q

PV Loop w Decreased Compliance

A
  • loop moves closer to the horizontal axis
  • high compliance = closer to vertical axis
  • dotted line = normal compliance
67
Q

Increased Compliance PV Loop with PEEP

A
  • decreased compliance (dotted line) improved w use of PEEP
  • PEEP recruits more alveoli, increasing ability of lungs to expand
68
Q

What should you do if PEEP doesn’t improve compliance?

A
  • remove PEEP if not beneficial
  • problem may be reisistance so a bronchodilator should be used
69
Q

Pediatric PV Loop

A
  • compliance lower in peds due to lower TV and lung development
  • higher pressure required to overcome resistance of ETT
  • chest wall compliance greater in peds
  • PEEP beneficial due to low lung compliance
70
Q

Increased Resistance PV Loop

A
  • higher pressure needed to deliver same volume (solid curve)
  • TV may be reduced
  • PV loop shifted to the right and down w large internal area (increased WOB)
  • pressure falls rapidly after inspiration complete
71
Q

What does an open loop indicate?

A
  • air trapping
  • not getting out the volumes you put in
72
Q

Directional Flow of Spont vs Vent Breaths

A
  • spontaneous breaths = clockwise
  • ventilator breaths = counterclockwise
73
Q

PV Loop Spontaneous w Increased Resistance

A
  • normal loop = dotted line
  • w increased resistance, greater pressure (more negative during insp, more positive during exp) will be needed to move the same volume of gas (increased WOB)
74
Q

Pressure-Volume Loop Severe COPD

A
  • resistance during exp increased
  • open loop
75
Q

Flow-Volume Loop Severe COPD

A
76
Q

Flow-Volume Loop w Fixed Intra- or Extra-thoracic Obstruction

A
77
Q

Flow Volume Loop w Extrathoracic Obstruction

A
  • obstruction outside thorax will cause plateau during inspiration
  • expiratory portion close to normal (dotted line)
78
Q

Flow-Volume Loop w Intrathoracic Obstruction

A
  • may be tumor in trachea or mediastinal mass
  • inspiratory flow may be normal but during expiration, flow rises to plateu instead of peak
79
Q

Flow-Volume Loop w Restrictive Ventilatory Defect

A
  • increase in elastic recoil is associated w higher expiratory flows
  • as severity increases and volumes are decreased, loop becomes tall and narrow
80
Q

PV Loop w Secretions in Tracheal Tube

A
81
Q

Flow-Volume Loop w Secretions in Tracheal Tube

A
82
Q

Pressure-Volume Loop with Spontaneous Breath

A
83
Q

Flow-Volume Loop w Spontaneous Breath

A
  • spont breath occurs near end expiration
  • instead of returning to 0, flow increases and there is a small increase in volume
84
Q

PV and FV Open Loops

A
  • leak exists, so exhaled volume is 150mL less than inhaled volume
  • produces open loops
  • seen w uncuffed ETT in peds
85
Q

PV and FV Loops w Air Trapping/Intrinsic PEEP

A
  • gap in flow-vol loop indicates there was still expiratory flow when next breath commenced
86
Q

PV and FV Loops, Misconnection of Tubing

A
  • loop drawn backwards and upside-down
87
Q

PV and FV Loop w Disconect

A
  • no flow through sensor
88
Q

PV and FV Loop w Leak Between Sensor and Breathing System

A
  • loop has normal shape but TV, PP and Exp Flows are decreased
  • dotted = normal, solid = loop w leak
89
Q

PV Loop w Bronchial Intubation

A
  • results in decreased compliance
90
Q

PV and FV Loop, Esophageal intubation

A
  • varies greatly. Compliance may be increased, decreased, or normal
91
Q

PV Loop w Nearly Complete Obstruction

A
  • high pressure, little volume

Anesthesia Equipment Exam 2 (6 decks)

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