AMDS Y1FA23 Flashcards
Lung Compliance Formula
ΔVolume/ΔPressure (mL/cmH2O)
Change in volume/ Change in pressure
Decreased compliance means what in terms of Ventilation?
a greater change in pressure is needed for
a given change in volume
Examples of decreased lung compliance
atelectasis, edema, fibrosis, pneumonia,
or absence of surfactant
Static Compliance
= Exhaled Tidal Volume (Vte)/Plateau Pressure (Pplat) – Positive End Expiratory Pressure (PEEP)
Dynamic Compliance formula
Exhaled Tidal Volume (Vte)/Peak Inspiratory Pressure (PIP) – Positive End Expiratory Pressure (PEEP)
Normal Adult Lung Compliance
40-70 mL/cmH
Normal Child lung compliance
About 1mL/cmH2O/kg
Lung Elastance formula
ΔPressure/ ΔVolume (cmH2O/mL)
Change in pressure over the change in volume
How are lung compliance and Elastance related?
Compliance and elastance are inversely related
* If compliance increases, then elastance decreases
* If compliance decreases, then elastance increases
Elastance Definition
A measure of the tendency of something to recoil toward its
original dimensions upon removal of a distending or
compressing force
Lung Compliance Definition
A measure of the ease of expansion of
the lungs and thorax, determined by
pulmonary volume and elasticity
A high degree of compliance in the lungs indicates
a loss of elastic recoil of the lungs, as in
old age or emphysema
Airway pressure formula
Δ Pressure/Flow (cmH2O/L/sec)
Change in pressure over flow
Airway Resistance
the friction caused by the movement of air throughout the respiratory system
Types of Flow:
Laminar
Turbulent
Tracheobronchial
Laminar Flow
Smooth, even non-tumbling flow
Turbulent Flow
Rough, tumbling uneven flow pattern
– The pressure gradient necessary to maintain turbulent flow is much higher than that necessary to maintain laminar flow
Tracheobronchial Flow
A combination of laminar and turbulent flow which is maintained throughout the respiratory system
Airway resistance decreases with
increased airway diameter, bronchodilation, laminar flow and increase in lung volume
Airway resistance increases with
decreased airway diameter, bronchoconstriction, turbulent flow and decrease in lung volume
Normal airway Resistance:
0.5-2.5cmH2O/L/sec at a flow rate of 0.5 L/sec
Types of Manual Ventilation
Control Modes
Synchronized Modes
Support Modes
Control mode of Ventilation
Positive pressure ventilation in which the ventilator is in control mode, with its cycle entirely controlled by the apparatus and not influenced by the patient’s efforts at spontaneous ventilation
Synchronized mode of Ventilation
Synchronized Intermittent Mechanical
Ventilation is a variation of IMV, in which
the ventilator breaths are synchronized
with patient inspiratory effort, with
added pressure support.
Support Mode of Ventilation
The patient initiates every breath and
the ventilator delivers support with the
preset pressure value. With support
from the ventilator, the patient also
regulates his own respiratory rate and
tidal volume.
VCV Primary Setting
Tidal Volume
Constant inspiratory Flow
PCV-VG primary Setting
Tidal Volume
Decelerating inspiratory Flow
PCV Primary Setting
inspiratory pressure
Decelerating inspiratory Flow
Synchronized Ventilation modes
SimV-VCG
SIM-V- PCVVG
SIM V- PCV
Support modes of Ventilation
CPAP/ PS (PEEP)
PSV-PRO (Pressure Support)
Trigger Window in Mechanical Ventilation
A percentage of end expiratory time that a patient
can trigger a mechanical breath – Adjustable from 0-80%
If the ventilator senses the beginning of inspiration
within the trigger window, what happens?
it delivers the next volume, pressure or PCV -VG breath and inspiratory time set on the ventilator
If the patient does not make an inspiratory effort
within the trigger window, what happens?
the ventilator will deliver a machine breath to the patient
Any breath outside of the trigger window will be
a pressure supported breath, if set
Trigger window settings are available on which ventilator modes?
all SIMV modes
Flow Triggering:
Synchronizes SIMV and
Pressure supported breath delivery with the
patient’s effort
Flow Trigger:
Adjustable negative flow (0.2 – 10
L/min) needed to trigger a mechanical breath
How is Flow trigger measured?
by the inspiratory flow sensor
How does the flow trigger work?
Improves synchronization of breaths
decreasing a patient’s tendency to fight the
ventilator
Volume Control Ventilation (VCV)
The ventilator delivers mechanical breaths of the set tidal
volume at intervals based on the set respiratory rate
– The amount of pressure required to deliver the tidal volume
depends on the patient’s lung compliance and resistance
VCV is ideal for what kind of patient?
a patient with normal compliance, low airway
resistance and need for consistent, non-synchronized
breaths
Pressure Control Ventilation (PCV)
The ventilator delivers mechanical breaths at the set
inspiratory pressure level during inspiration
* The ventilator calculates the inspiratory time from the
frequency and I:E ratio settings
– The tidal volume delivered depends on the patient’s
lung compliance
In PCV, the volume delivered depends on what?
patient’s lung compliance
Pressure Control Ventilation-Volume Guarantee (PCV-VG)
The ventilator delivers mechanical breaths of the set tidal
volume at intervals based on the set respiratory rate. For each
breath, the ventilator adjusts the inspiratory pressure to use
the lowest pressure required to deliver the tidal volume
– Delivers breaths with the efficiency of pressure controlled ventilation
– Compensates for changes in the patient’s lung characteristics
In PCV-VG, To determine the patient’s lung compliance, the ventilator
the ventilator
delivers volume-controlled breath
– Based on the patient’s lung compliance, the inspiratory pressure is
established for subsequent breaths
– When adjusting the inspiratory pressure the following pressure range is
used:
* Low end: PEEP+2 cmH2O
* High end: Pmax-5 cmH2O
– The difference in inspiratory pressure between breath
does not exceed +/- 3 cmH2O
Best clinical situations for PCV-VG
Laparoscopic
Major Trauma
Cardiac
SIMV VCV
Synchronized Intermittent Mandatory Ventilation
Volume Control Ventilation
SIMV VCV
- The ventilator delivers synchronized mechanical breaths of a set
tidal volume at intervals based on a set respiratory rate. All other
spontaneous efforts are delivered as pressure-supported breaths
– The amount of pressure required to deliver the tidal volume depends on
the patient’s lung compliance and resistance
– The ventilator will always deliver the specific number of breaths per
minute the clinician has set
– I:E is replaced by an inspiratory time (Tinsp)
– Between machine breaths, the patient can breath spontaneously at the
rate, tidal volume and timing that the patient desires
In SIMV-VCV, The ventilator calculates an inspiratory flow based on
the set tidal
volume, inspiratory time and Tpause, if set
– Flow is constant and maintained during the inspiratory phase while
airway pressure is below the pressure limit
– Adjustable pressure limit terminates the breath if peak pressure is
reached
In SIMV-VCV, a color change in the waveform indicates
Spontaneous breaths from the patient
Trigger window, Rise Rate, Flow Trigger and End of Breath are all
active in this mode of ventilation?
SIMV-VCV
SIMV-PCV-VG
SIMV-PCV
PSV-Pro
CPAP-PSV
SIMV PCV
Synchronized Intermittent Mandatory Ventilation
Pressure Control Ventilation
SIMV PCV
The ventilator delivers synchronized mechanical breaths at the set
inspiratory pressure level for a set inspiratory time at intervals based on
the set respiratory rate. All other spontaneous efforts are delivered as
pressure-supported breaths
– The tidal volume delivered depends on the patient’s
lung compliance
– The ventilator will always deliver the specific number of breaths per minute the clinician has set
– I:E is replaced by an inspiratory time (Tinsp)
– Between machine breaths, the patient can breath spontaneously at the rate, tidal volume and timing that the patient desires
In SIMV-PCV, the tidal volume delivered depends on what?
the patient’s lung compliance
True/False:
In SIMV-PCV, the patient cannot take spontaneous breaths
FALSE:
Between machine breaths, the patient can breath spontaneously at the rate, tidal volume and timing that the patient desires
SIMV PCV-VG
Synchronized Intermittent Mandatory Ventilation Pressure Control
Ventilation-Volume Guarantee
SIMV-PCV-VG
The ventilator delivers synchronized mechanical breaths of the set tidal volume at
intervals based on the set respiratory rate. For each mechanical breath, the
ventilator adjusts the inspiratory pressure to use the lowest pressure required to
deliver the tidal volume. All other spontaneous efforts are delivered as pressure supported breaths
In SIMV-PCV-VG
To determine the patient’s lung compliance, the ventilator does what?
delivers volume-controlled breath
In SIMV-PCV-VG
0.5 cmH2O less than the current breath’s pressure target
PSVPro
The ventilator provides a constant support pressure once it senses the
patient has made an inspiratory effort
PSVPro is intended for what type of patient?
Intended to be used on spontaneously breathing patients
What is the apnea mode as a backup to PSVPro
An apnea backup mode of SIMV PCV is provided if the patient stops
breathing
– Backup time can be set between 10-30 seconds
After the patient is apneic on PSVPro and goes into backup mode (SIMV-PCV), When does PSVpro resume?
PSVPro automatically resumes when the ventilator registers the number of
consecutive patient triggered breath set for Exit Backup
* Exit Backup range Off, 1-5 spontaneous breaths
* When Exit Backup is set to off, the user must reselect PSVPro mode to reactivate PSVpro
When in PSVPro and the vent is triggered to backup mode (SIMV-PCV), what setting prevents the ventilator from returning to PSVPRO?
When Exit Backup is set to off, the user must reselect PSVPro mode to reactivate PSVpro
CPAP + PSV
Continuous Positive Airway Pressure + Pressure Support
Ventilation
CPAP + PSV
The ventilator provides a constant support pressure once it senses the
patient has made an inspiratory effort
– Intended to be used on spontaneously breathing patients
– The clinician sets the pressure support and PEEP levels
– Patient initiates spontaneous breaths and determines respiratory rate, timing, and tidal volume
In CPAP- PSV
If the spontaneous inspiratory effort does not occur within the delay
period, the ventilator
delivers pressure controlled breaths at the preset
inspiratory pressure to meet the set minimum rate
– The delay period calculation is 60s/minimum rate + ([60s/minimum rate] –previous measured breath period)
PSVPro and CPAP + PSV indications
All operations where spontaneous breathing does not
interfere with surgical procedure
Cases with spontaneous breathing using an artificial
airway
Ideal for laryngeal mask (Ppeak reduced compared with
mechanical ventilation with equal TV)
Advantages of Volume Controlled Ventilation
- Constant tidal volume
- Consistent alveolar ventilation
- Easily identify changes in PIP and Pplat as respiratory
mechanics change
Advantages of pressure controlled ventilation
- PIP and peak alveolar pressures are constant
- Flow varies with patient demand
Advantages of Pressure Control Ventilation-Volume Guarantee
- Targeted tidal volume
- Pressure automatically adjusts based on
lung compliance and airway resistance - Decelerating waveform
- Variable inspiratory flow to meet
patient’s demand
Disadvantages of VCV modes
Constant flow rate
* Increase in potential asynchronies
* Varying pressures
Disadvantages of PCV modes
Varying tidal volumes
Disadvantages of PCV-VG Mode
Pressure adjusts based on the tidal volume
of the last breath
* Asynchronies may occur with variable
patient effort
How is tidal volume changed in reduced lung compliance?
Smaller Tidal Volume delivered
How do ventilators generate gas flow?
by creating pressure gradient between the proximal airway and the alveoli.
four phases of the ventilatory cycle:
Inspiration
◦ Transition from inspiration to expiration
◦ Expiration
◦ Transition form expiration to inspiration
Termination of the inspiratory phase can be triggered
by what and depends on?
Preset limit of time
◦Set inspiratory pressure that must be reached
◦Predetermined tidal volume that must be delivered
depending on the ventilators mode at that moment.
In the expiratory phase, flow out of the lungs is determined by
Airway resistance and lung compliance
This phase, together with the transition
from I to E phase, determine the
ventilator mode
transition from E: I
VCV
◦ Vt and RR are
Fixed
PCV
◦ PIP and RR are
Fixed
Double circuit system ventilator
Contains a free breathing valve that allows
outside air to enter the rigid drive chamber and the bellows to collapse if the patient generates negative pressure during mechanical ventilation.
Peak Inspiratory Pressure (PIP)
Is the highest pressure generated during an inspiratory cycle
PIP is an indication of
Dynamic Compliance
Plateau pressure (PP) is measured
during
an inspiratory pause (a time of no gas flow)
Plateau pressure is an indication of
static compliance
Pulmonary edema
◦ T-berg
◦ Pleural effusion
◦ Ascites
◦ Peritoneal gas insufflation
◦ Tension pneumothorax
◦ Endobronchial intubation
all indicators of
decreased pulmonary compliance
Kinked ETT
◦ Bronchospasm
◦ Secretions
◦ Foreign body aspiration
◦ Airway compression
◦ ETT cuff herniation
All indicators of
Increased airway resistance
Increased PIP and PP indicates
Increased Vt
◦ Decreased pulmonary compliance
Increased PIP and unchanged PP
◦ Increased inspiratory gas flow rate
◦ Increased airway resistance
A target variable
one that can reach and maintain a preset level before inspiration
ends, it does not end inspiration
◦ Also known as limit variables
In PCV, Tidal Volume (Vt) is
variable
In VCV, Tidal volume (Vt) is
Constant
In PCV, PIP is
Constant
In VCV, PIP/ Pplat is
Variable
In PCV, flow pattern and peak flow are
Variable
In VCV, Flow pattern and peak flow are
Set
In PCV and VCV, inspiratory time is
SET
