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N928 - Basics of Anesthesia > Ventilator Settings > Flashcards

Ventilator Settings Flashcards

1
Q

fraction of inspired oxygen (FiO2)

A

concentration of oxygen in the inspired gas; can be set from 0.21 (room air) to 1.0 (100%)

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2
Q

tidal volume (Vt)

A

volume of gas, either inhaled or exhaled, during a breath and commonly expressed in mL; Vt generally set between 8-12 mL/kg (better practice for LPV is 6-8 mL/kg to prevent lung overdistention and injury)

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3
Q

respiratory rate (RR) or frequency

A

number of breaths per minute that the ventilator delivers; commonly set between 10-20 breaths per minute; if patient is making spontaneous respiratory efforts, RR will be higher

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4
Q

minute ventilation (VE)

A

average volume of gas entering, or leaving, the lungs per minute; commonly expressed in L/min; Vt x RR = VE; normal VE is between 5-10 L/min

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5
Q

peak flow rate OR peak inspiratory flow

A

the highest flow or speed that is set to deliver the Vt during inspiration; usually measured in L/min; when flow rate is high, the speed of gas delivery is faster and inspiratory time is shorter

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6
Q

inspiratory time

A

time spent in the phase of inspiration

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7
Q

expiratory time

A

time spent in the phase of expiration

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8
Q

I/E ratio

A

the speed at which the Vt is delivered; setting a shorter i time results in a faster inspiratory flow rate; average adult inspiratory time is 0.7 to 1.0 s; I/E is usually 1:2 or 1:3

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9
Q

peak airway pressure (Paw)

A

represents the total pressure that is required to deliver the Vt and depends upon various airway resistance, lung compliance, and chest wall factors; expressed in cm H2O

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10
Q

plateau pressure (Pplat)

A

the pressure needed to distend the lung, which can be measured by applying an end-inspiratory pause setting on the ventilator; it is expressed in cmH2O

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11
Q

sensitivity or trigger sensitivity

A

effort or negative pressure required by the patient to trigger a machine breath, commonly set so that minimal effort (-1 to -2 cmH2O) is required to trigger the breath; some vents may have flow triggering which is more sensitive than pressure triggering if flow setting is set correctly; a decrease in flow is sensed when patient makes a spontaneous effort and triggers the machine to deliver the breath

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12
Q

Positive end expiratory pressure (PEEP)

A

amount of positive pressure that is maintained at end-expiration; expressed in cmH2O; purpose is to increase end-expiratory lung volume and reduce air-space closure at end-expiration

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13
Q

continuous positive airway pressure (CPAP)

A

continuous pressurization of the breathing circuit when a patient breaths spontaneously; may be used as a last step in the weaning process or as a noninvasive method of providing a pneumatic splint to the upper airway in OSA

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14
Q

mandatory breath

A

a breath in which the timing and/or size of the breath is controlled by the ventilator; the machine triggers and/or cycles the breath

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15
Q

spontaneous breath

A

a breath in which both the timing and size are controlled by the patient; the patient both triggers and cycles the breath

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16
Q

A/C

A

assist control

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17
Q

CMV

A

controlled mechanical ventilation OR continuous mandatory ventilation

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18
Q

PSV

A

pressure support ventilation

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19
Q

PCV

A

pressure control ventilation

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20
Q

SIMV

A

synchronized intermittent mandatory ventilation

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21
Q

VCV

A

volume controlled ventilation

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22
Q

volume targeted mode of ventilation volumes

A

volume constant –> guarantees volume at expense of variable airway pressure

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23
Q

volume targeted mode of ventilation inspiration

A

inspiration terminates when present Vt is delivered

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24
Q

volume targeted mode of ventilation preset Vt delivered

A

unless a specified pressure limit is exceeded (upper airway pressure alarm is set) or patient’s cuff or ventilator tubing has air leaks that cause a decrease in Vt delivered

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25
Q

volume targeted mode of ventilation peak airway pressure

A

variable; determined by changes in airway resistance, lung compliance, or extrapulmonary factors; the peak airway pressure increases as needed to deliver prescribed Vt

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26
Q

volume targeted mode of ventilation inspiratory flow rate

A

fixed; if patient inspires faster or more vigorously, work of breathing increases; clinician needs to promptly correct airway resistance and/or lung compliance problems, readjust flow-rate setting higher to match inspiratory demands

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27
Q

examples of volume targeted vent modes

A

CMV, VCV, A/C, SIMV

28
Q

pressure targeted modes volume

A

volume variable; guarantees pressure at expense of letting Vt vary

29
Q

pressure targeted modes inspiration

A

inspiration terminates when preset pressure reached; preset pressure delivered and volume is variable and determined by the set pressure level, airway resistance, and lung compliance factors, specified time or flow cycling criteria

30
Q

pressure targeted modes peak airway pressure

A

fixed; determined by set pressure level; volume delivered is variable and decreases with increased airway resistance, decreased lung compliance, or extrapulmonary factors

31
Q

pressure targeted modes inspiratory flow rate

A

variable; if patient inspires faster or more vigorously, variable flow rate may match change in inspiratory demand or may be insufficient; clinician needs to promptly correct airway resistance and/or lung compliance problems, may need to readjust pressure support or I/E settings

32
Q

goals of mechanical ventilation in OR

A
  • maintain homeostasis
  • ensure adequate oxygenation
  • ensure adequate CO2 removal
  • safe and effective surgery
33
Q

PiP

A
  • peak inspiratory pressure
  • total pressure required to distend lungs and airways
  • pressure used to calculated dynamic compliance
34
Q

Pplat

A
  • plateau pressure
  • distending pressure to expand only the LUNGS
  • measure’s redistribution of air flow through lungs
  • Pplat is used to calculate static compliance
  • performed with an inspiratory hold in VCV only
  • tells us about the intrinsic pressure in the lungs
35
Q

4 parts of a breath

A
  • start of inspiration
  • inspiration itself
  • end of inspiration
  • expiration
36
Q

components of a breath

A
  • Ti = inspiratory time
  • Te = expiratory time
  • TCT = total cycle time
37
Q

total respiratory cycle variables

A
  • trigger variable (start of inspiration)
  • limit [or target] variable (maintenance of inspiration)
  • cycling variable (transition of expiration)
  • baseline variable (end expiration)
38
Q

trigger variable

A
  • represents start of inspiration

- can be affected with or without patient inspiratory effort by either pressure, volume, flow, or time

39
Q

pressure as trigger variable

A

pressure decrease in circuit stimulates ventilator to deliver breath

40
Q

volume as trigger variable

A

volume change in circuit can stimulate ventilator to deliver breath

41
Q

flow as trigger variable

A

change of flow in circuit stimulates ventilator to deliver breath

42
Q

time as trigger variable

A

set time interval triggers ventilator to deliver breath; this occurs independent of patient effort; this is what we see most common because we are using NMBDs

43
Q

limit [or target] variable

A

controls how an inspiratory breath is maintained, once threshold is reached variable will not exceed set limit; this does NOT cause termination of inspiration

44
Q

pressure as limit variable

A

sets upper pressure limit that cannot be exceeded

45
Q

volume as limit variable

A

sets upper volume limit that cannot be exceeded

46
Q

flow as limit variable

A

sets maximum airflow that cannot be exceeded; most common in assist control mode in ICU

47
Q

cycling variable

A

transition from inspiration to expiration; based on volume, pressure, flow or time

48
Q

volume as cycling variable

A

ventilator delivers flow until set volume achieved; if inspiratory pause set (typically 10-20%), this variable changes to a time-based cycling variable

49
Q

pressure as cycling variable

A

once pressure is achieved, flow will transition to expiration

50
Q

flow as cycling variable

A

once inspiratory flow drops below set threshold (default at 25%) ventilator will transition to expiration; noted in pressure support ventilation mode

51
Q

time as cycling variable

A

ventilator terminates inspiratory breath after predetermined inspiratory time has been delivered; most common because we use NMBD

52
Q

baseline variable

A
  • pressure maintained in the circuit at end expiration (PEEP)
  • must be individualized to patient
  • used to prevent atelectasis
53
Q

PEEP

A
  • alveolar pressure above atmospheric

- goal = improved oxygenation and ventilatory mechanics

54
Q

intrinsic PEEP

A
  • secondary to incomplete expiration; referred to as auto-PEEP; incomplete expiration prior to initiation of next breath; causes progressive air trapping
  • causes –> high minute ventilation; expiratory flow limitation; expiratory resistance
55
Q

extrinsic PEEP

A

provided by a mechanical ventilator; referred to as applied PEEP

56
Q

volume control ventilation (VCV)

A
  • delivers set tidal volume at respiratory rate
  • time is trigger variable
  • volume is the limit variable
  • time is the cycling variable
  • airway pressure (PIP/Pplat) will change on a breath-by-breath basis during this mode of ventilation based on changing respiratory compliance
  • airflow will remain constant
  • *NOTE airway pressure on VCV will be upside down V
57
Q

why choose VCV?

A
  • maintenance of set minute ventilation through direct manipulation of Vt and RR
  • must set individualized alarms for airway pressure to protect patient
  • increasing airway or lung resistance will stimulate generation of higher pressure to deliver set Vt
58
Q

pressure control ventilation (PCV)

A
  • delivers set inspiratory pressure at set RR
  • time is trigger variable
  • pressure is the limit variable
  • time is the cycle variable
  • airway pressures are controlled by the user, Vt can change on a breath-by-breath basis depending on total respiratory system compliance
59
Q

why choose PCV?

A
  • set pressure limit to avoid barotrauma from delivery of excessive pressure
  • decelerating flow pattern allows for homogenous distribution of inspired gas throughout lungs; theoretically improves ventilation pattern and decreases WOB
  • must set patient appropriate high and low Vt alarms as change in respiratory compliance can affect Vt delivered
60
Q

pressure control-volume guarantee (PCV-VG)

A
  • respiratory cycle variables mirror PCV, however ventilator adjusts pressure delivered if current volume is not set volume
  • adjustments take 3-5 breaths to complete; vent will switch in to a volume mode to determine the pressure it needs to deliver
  • can allow for atelectasis development if compliance decreases and ventilator is delayed in providing adequate pressure to distend lungs
61
Q

synchronized intermittent mandatory ventilation (SIMV)

A
  • delivers set Vt at set RR in conjunction with patient initiated breaths
  • time or patient stimulate the trigger variable
  • flow is the limit variable
  • time or volume is cycle variable; most likely time in the OR
  • patient initiated breaths are not supported (unless in SIMV-PSV)
62
Q

why choose SIMV?

A
  • useful when weaning from controlled mechanical ventilation to spontaneous respiration; less dyssynchrony with patient initiated breaths
  • hypoventilation can occur if set Vt and RR are too low and patient’s spontaneous respiration effort inadequate
  • hyperventilation can also occur if using SIMV-PSV and pressure support level too high
63
Q

pressure support ventilation (PSV)

A
  • supported mode of ventilation for spontaneously breathing patient
  • pressure support level set by user
  • patient is the trigger variable
  • pressure is the limit variable
  • flow is the cycle variable
  • patient controls most aspects of ventilation, but anesthetist can adjust certain variables to augment or limit support given to prepare patient for extubation
64
Q

why choose PSV?

A
  • great for end of case in preparation for extubation; patient must be breathing spontaneously or ventilator will switch to backup mode
  • just like PCV pressure is controlled, changes in respiratory system compliance will alter Vt delivered
65
Q

flow trigger

A

L/min required for the ventilator to sense that a patient is triggering a breath; the lower the flow trigger is set at, the more sensitive the ventilator is to any adjustment in flow through the circuit; if flow of any kind is sensed a breath will be triggered

66
Q

trigger window

A

backup mode of SIMV-PSV; the percentage of time that the patient’s breath will be supported; if the patient initiates a breath within that % window, then the breath will be supported; if it is outside the % the breath will not be supported

67
Q

backup time

A

when you change patient from PCV to PSV, how long the patient is allowed to be apniec before the backup mode on the ventilator is triggered

N928 - Basics of Anesthesia (17 decks)

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