Modes of Mechanical Ventilation Flashcards
(98 cards)
1
Q
What is the fundamental waveform of volume controlled breathing?
A
square wave
2
Q
What is the fundamental waveform of pressure controlled ventilation?
A
ramp wave
3
Q
What is peak inspiratory pressure (PIP or Paw)?
A
peak pressure in the airway as a product of airway resistance
4
Q
What is plateau pressure (Pplat)?
A
pressure needed to distend the lung as a product of lung compliance
5
Q
What occurs during the slight drop in pressure from PIP to Pplat?
A
air dissipates out of the lungs and causes a slight drop in pressure
6
Q
What are mechanical ventilation variables?
A
elements of a breath that a ventilator can control during delivery of the breath
7
Q
What are the two kinds of mechanical ventilation variables?
A
Control variables
phase variables
8
Q
What is a control variable?
A
the primary variable that the ventilator control circuit manipulates to cause inspiration; controls the “shape” of the delivered breath
9
Q
What are the 3 variables that a ventilator can control?
A
Pressure
Volume
Flow
10
Q
Can more than one variable be directly controlled at a time?
A
No, can only be pressure, volume, or flow controlled
11
Q
What is volume controlled ventilation?
A
volume and flow waveforms remain unchanged with changes in respiratory mechanics but pressure will vary
12
Q
What is pressure controlled ventilation?
A
pressure waveform will remain unchanged with changes in respiratory system mechanics but volume and flow will vary
13
Q
What are the 4 phases of a complete breath or respiratory cycle?
A
- start of inspiration
- inspiration itself
- ending of inspiration
- expiration
14
Q
What are phase variables that control the conventional phases of the respiratory cycle?
A
Trigger variable
Limit (target) variable
Cycle variable
Baseline variable
15
Q
What is the role of the trigger variable?
A
starts inspiration
16
Q
What is the role of the limit (target) variable?
A
ensures limit is reached and maintained at preset level before inspiration ends
17
Q
What is the relationship between the cycling variable and respiratory cycle?
A
ends inspiration and begins expiration
18
Q
What is the role of the baseline variable?
A
ensures baseline condition controlled at end expiration, most often controls pressure at end-exhalation
19
Q
What occurs with pressure as a trigger variable?
A
pressure drop in the circuit as a result of the patient’s attempt to inhale is sensed by the ventilator delivers a breath in response to it (patient effort required)
20
Q
What occurs with flow as a trigger variable?
A
the flow into the circuit as a result of the patient’s attempt to inhale is sensed by the ventilator, and the ventilator delivers a breath in response to it (patient effort required)
21
Q
What occurs with volume as a trigger variable?
A
the volume change in the circuit as a result of the patient’s attempt to inhale is sensed by the ventilator and the ventilator delivers a breath in response to it (patient effort required)
22
Q
What occurs with time as a trigger variable?
A
the breath is triggered according to a preset frequency , and is delivered at regular intervals of time, independent of patient effort
23
Q
What occurs with pressure as a limit variable?
A
the set upper pressure limit cannot be exceeded during inspiration (used with pressure control ventilation)
24
Q
What occurs with volume as a limit variable?
A
the set volume cannot be exceeded during the inspiration (used with volume controlled ventilation)
25
What occurs with flow as a limit variable?
the flow limit cannot be exceeded during inspiration (used with volume control ventilation)
26
What occurs with volume as a cycling variable?
the ventilator cycles from inspiration to expiration by delivering flow until a preset volume has been delivered (e.g. volume control mode)
27
What happens with volume as a cycling variable when an inspiratory pause has been set?
expiration does not immediately follow the delivery of a breath and becomes time cycled rather than volume cycled
28
What happens when time is a cycling variable?
ventilator cycles from inspiration to expiration by delivering flow until a preset inspiratory time has elapsed (e.g.pressure control mode); related to I:E ratio
29
What happens when flow is the cycling variable?
when flow during inspiration falls to a certain level (typically 25% of the peak inspiratory flow), the ventilator cycles from inspiration to expiration (e.g. pressure support ventilation)
30
What happens when pressure is the cycling variable?
flow is provided until airway pressure reaches the set maximum airway pressure limit, the ventilator will cycle to expiration regardless of the tidal volume that has been delivered (pressure controlled ventilation)
(tidal volume and flow are dependent the pressure setting)
31
How is the baseline variable achieved?
Closure of the expiratory valve before lung has completely emptied
32
What is ZEEP?
Zero end expiratory pressure, baseline pressure set to zero relative to atmospheric pressure
33
What is PEEP?
positive end expiratory pressure, baseline pressure set positive relative to atmospheric pressure
34
What is a ventilator mode?
Refers to how the ventilator initiates a breath, how the ventilator delivers the breath, and how the breath is terminated
35
What are some considerations when choosing a vent mode?
Clinician familiarity
Institutional preferences
Surgery
Patient status
36
What are the different volume controlled modes?
Volume control ventilation (VCV)
Volume assist/control ventilation (ACV)
Intermittent mandatory ventilation (IMV)
Synchronized intermittent mandatory ventilation (SIMV)
Synchronized intermittent mandatory ventilation + pressure support ventilation (SIMV + PSV)
37
What are some indications for volume control?
- desire for constant tidal volume or minute ventilation (reduce atelectasis or maintain desired PaCO2)
- desire for steady-state inspiratory flow and maximum inspiratory pressure is not a concern (tidal volume and inspiratory flow are preset and fixed; airway pressure is variable and dependent on those settings and respiratory system resistance and compliance)
38
What is volume control ventilation?
a set tidal volume is delivered at a constant flow rate and set RR
39
What is the trigger, limit, cycle, and baseline for VCV?
Trigger: time
Limit: flow
Cycle: volume
Baseline: PEEP if desired
40
What are the typical initial settings for VCV?
tidal volume: 6-12 mL/kg
RR: 8-12 BPM
I:E ratio: 1:2
PEEP: 5 cm H2O
41
When is inspiration terminated in VCV?
when set tidal volume is delivered (or when excessive pressure is achieved and high pressure alarm sounds...usually 60-90 cm H2O)
42
In VCV, ____ is adjusted to reduce atelectasis and ____ is adjusted to maintain a desired PaCO2.
tidal volume, RR
43
With VCV, what happens to PIP when compliance decreases?
PIP increases, PIP is monitored but NOT controlled in VCV
44
What is volume assist-control ventilation (ACV)?
a set tidal volume is delivered at a constant flow rate and set RR, pt can breathe above the set rate and trigger the ventilator (by reduction in pressure or flow rate)
45
What is the trigger, limit, cycle, and baseline for ACV?
Trigger: Time (controlled ventilation) or pressure/flow (assisted ventilation)
Limit: Flow
Cycle: Volume
Baseline: PEEP if desired
46
Which vent mode is most often used in ICU ventilatory support?
volume assist-control ventilation (ACV)
47
What are some advantages of ACV?
- minute ventilation is guaranteed
- set tidal volume is guaranteed
- patient can choose to over-breathe the set RR
- each breath is delivered in synchrony with the patient's spontaneous effort; this makes for more comfortable breathing
- mode affords rest to the patient and unloads the respiratory muscles
48
What are some disadvantages of ACV?
- breathing schedule is relatively rigid; alkalosis may occur if the set RR is too high
- airway pressures may rise if lung mechanics are poor; dynamic hyperinflation can occur
- work of breathing can be high if the trigger sensitivity or flow settings are not appropriately adjusted
- sedation often required
- due to prolonged unloading of the respiratory muscles, ATROPHY IS POSSIBLE
49
What are the typical initial settings for ACV?
- present tidal volume and RR
- ventilator or patient triggered breath is delivered at the preset tidal volume
- patient determines own RR as long as spontaneous RR EXCEEDS the ventilator set rate
- if patient RR falls below the set rate the patient will be ventilated at the set rate
50
What is intermittent mandatory ventilation?
a set tidal volume is delivered at a constant flow rate and set RR; inbetween mandatory breaths patient can breathe spontaneously at their desired RR
51
Which volume controlled vent mode is principally used for weaning?
Intermittent mandatory ventilation (IMV)
52
What is the trigger, limit, cycle, and baseline for IMV?
Trigger: time (mandatory breaths occur at equal time intervals)
Limit: Flow
Cycle: Volume
Baseline: PEEP if desired
53
In IMV mode, are spontaneous breaths supported?
no
54
What are some disadvantages of IMV?
- Tidal volume depends on patient's inspiratory muscle effort
- Hypoventilation can occur if mandatory rate does not meet most of the minute ventilation requirements
- Asynchrony between mandatory and spontaneous breaths can produce "breath stacking"
55
Which volume control vent mode is used to allow exercising of the respiratory muscles?
SIMV
56
What is synchronized intermittent mandatory ventilation (SIMV)?
a set tidal volume is delivered at a constant flow rate and set RR; minimum number of mandatory breaths are synchronized with the patients respiratory effort
57
Are the patient's spontaneous breaths during SIMV mode assisted?
No
58
What is the trigger, limit, cycle, and baseline for SIMV mode?
Trigger: time/patient
Limit: Flow
Cycle: Volume
Baseline: PEEP if desired
59
What the primary advantage of using SIMV over IMV?
Allows the patient to breath spontaneously between mandatory breaths but synchronizes the mandatory breaths with the patient's spontaneous breathing effort (IMV does not synchronize the mandatory and spontaneous breaths)
60
What are other advantages of SIMV?
in between mandatory breaths patient can breathe at their predetermined RR, VT, and flow
allows patient to exercise respiratory muscles during mechanical ventilation and disuse atrophy is less common
61
What are some disadvantages of SIMV?
- work of breathing can be high if the trigger sensitivity and the flow are inappropriate to the patient's needs
- hypoventilation can occur if the patient cannot sustain spontaneous respirations and the mandatory rate has not been set high enough
- excessive work of breathing is possible during spontaneous breaths unless an adequate level of pressure support is applied (SIMV + PSV)
62
What is synchronized intermittent mandatory ventilation + pressure support ventilation? (SIMV + PSV)
- a set tidal volume is delivered at a constant flow rate and a set RR
- a minimum number of mandatory breaths are synchronized with the patient's respiratory effort
- spontaneous breaths taken between the mandatory breaths are support with positive inspiratory pressure
63
What is the trigger, limit, cycle, and baseline for SIMV + PSV?
Trigger: time/patient
Limit: flow/pressure
Cycle: volume/flow
Baseline: PEEP if desired
64
What are the different pressure controlled modes?
```
Pressure control ventilation (PCV)
SIMV + PSV
Pressure support ventilation (PSV)
PSV-Pro
Pressure control ventilation with volume guarantee (PCV-VG)
```
65
What are some indications for pressure control?
- desire to limit inspiratory pressure
- airway pressure waveform is preset by setting PIP and PEEP
- tidal volume and inspiratory flow are dependent on these settings and on respiratory system resistance and compliance
66
In which patient populations would you want to prevent high PIP?
emphysema
neonates/infants
LMA
67
Which patient populations would pressure control be a concern due to low compliance?
pregnancy
laparoscopic surgery
morbid obesity
ALI/ARDS
68
What is pressure control ventilation (PCV)?
- preset pressure limited breath is delivered at a set RR
| - supports apneic patient or unreliable respiratory drive
69
What is the trigger, limit, cycle, and baseline for PCV?
Trigger: time
Limit: pressure
Cycle: time
Baseline: PEEP as desired
70
What is not guaranteed with PCV?
tidal volumes, tidal volume given is based on airway resistance and lung compliance
71
What are some advantages of PCV?
- ability to maintain a desired peak airway pressure and inspiratory time
- DECELERATING FLOW PATTERN promotes more rapid alveolar filling and more even gas exchange (results in improved gas exchange, decreased work of breathing, and avoids overdistention of alveoli)
72
What is a disadvantage of PCV?
inability to maintain a fixed tidal volume and minute ventilation due to changes in respiratory compliance
73
What are the typical initial settings of PCV?
- preset pressure limit and RR
- initial RR 6-12 BPM
- I:E ratio of 1:2
- Initial pressure limit 20 cm H2O (recommended maximum distending pressure of 30 to 35 cm H2O)
- target tidal volume of 6 mL/kg IBW at these settings
- PEEP 5 cm H2O if desired
74
What is PSV useful for?
weaning/augment tidal volume during maintenance and emergence
75
What is required to use PSV?
spontaneously breathing patient, pt sets RR
76
What is PSV?
pt sets RR with spontaneous respirations and vent provides additional support to achieve optimal consistent tidal volume
77
What is the trigger, limit, and cycle for PSV?
Trigger: patient (pressure or flow)
limit: pressure
cycle: flow (decreases to a % of maximum value)
78
What does the patient control with PSV?
- depth, length, and flow of each breath
- for a given inspiratory effort a greater tidal volume is achieved but tidal volume and minute ventilation are NOT guaranteed
79
What are some advantages of PSV?
- patient can control the depth, length, and flow of each breath
- tends to be relatively comfortable and well tolerated
- patient triggering produces a greater volume and better synchronization with the ventilator
- minimizes the WOB; unloads the respiratory muscles
- low level of PSV negates the ETT resistance
80
What are some disadvantages of PSV?
- only pressure is assured, not tidal volume (with bronchospasm, pulmonary edema, or tube obstruction, tidal volumes will fall)
- excessive levels of support can result in:
respiratory alkalosis
hyperinflation
ineffective triggering
apneic spells
81
What can occur when PSV is used with COPD patients?
1. narrowed airways result in slow filling of lungs during inspiration
2. late into inspiration, flow rate remains high, well above the cycling threshold
3. ventilator fails to cycle to expiration even though patient's neurological inspiratory time has been completed
4. patient attempts to exhale while the ventilator is yet delivering the breath
5. patient-ventilator ASYNCHRONY
82
What is different about PSV-Pro mode?
- if no breaths are detected (PSV) an adjustable apnea delay period (10-30 secs), the ventilator switches to the back-up mode (PCV)
- if resumption of spontaneous breaths occurs, the ventilator will return to PSV mode
83
Which AGMs have PSV-Pro?
Datex
Ohmeda
Aisys
84
What can occur if the trigger setting is too sensitive during PSV-Pro mode?
- ventilator may deliver a pressure support breath as a result of surgical manipulation, cardiogenic oscillations or condensation in the breathing circuit
- RR could appear to be considerably higher than the patient's actual spontaneous RR
85
What can occur if the trigger setting is not sensitive enough with PSV-Pro mode?
the machine will fail to trigger and work of breathing will increase perhaps producing coughing and bucking
86
What are the two goals of PEEP?
improve oxygenation and re-expansion of collapsed alveoli
87
What is intrinsic PEEP?
secondary to incomplete expiration, referred to as auto-PEEP
88
What is extrinsic PEEP?
also known as applied PEEP, PEEP that is provided by a mechanical ventilator
89
What is physiologic PEEP?
3-5 cm H2O
| most surgical patients
90
What is supra-physiologic PEEP (excessive PEEP)?
ARDS/ALI
| pulmonary edema
91
What are some indications for PEEP?
intrapulmonary shunt
| decreased FRC
92
What are some physiologic effects of PEEP?
decreased venous return
increased ICP
altered renal function
barotrauma
93
What is auto-PEEP?
incomplete expiration prior to the initiation of the next breath causes progressive air trapping
94
What are causes of auto-PEEP?
high minute ventilation
expiratory flow limitation
expiratory resistance (secretions, small/kinked ETT, etc)
95
What is the dual mode of pressure regulated volume controlled mode? (PRVC)
- pressure controlled ventilations with volume guarantee (PCV-VG)
- created in response to variation in tidal volume with pressure control mode and changing lung compliance
- inspiratory pressure is continuously adjusted to ensure delivery of the set tidal volume using the LOWEST possible pressure
96
Describe how PCV-VG works.
1. ventilator delivers a volume breath at the set tidal volume
2. vent determines if the pressure applied during the breath is adequate to produce the set tidal volume
3. if not, the vent adjusts the pressure applied during the next breath to generate the desired tidal volume
4. vent effectively auto-regulates the inspiratory time and flow rate so the set tidal volume generates a smaller rise in the Pplat (plateau) pressure
97
What is the formula to determine airway resistance (Raw)?
R = PIP - Pplat/ inspiratory flow or time/min on vent
98
What is the formula to calculate lung compliance?
C = delta V/delta P
C = tidal volume/ Pplat - PEEP
