Mod 5 Vent Variables Flashcards
how do you determine if you match a patients O2 needs/requirements?
Good CNS function
good perfusion
etc. indeterminable without a mixed venous pressure/sample to get a better idea at the hemoglobin
i.e good LOC
What are the Vent. Mode basics?
volume control
Pressure control
pressure support
which pressure is maintain in all vent. modes?
PEEP (range 4-6;but set 5)
Keeps interalveolar airways open
What is oxygenation and ventilation controlled with?
Oxygenation: FiO2 and MAP
(hypoxic)
Ventilation: RR
(acidotic)
Vital capacity is a good measure of what?
our ability to cough (and help clear secretions
What is the purpose of ventilation?
-Supporting/manipulating gas exchange:
-Increase lung volume
-Reduce/manipulate WOB
-Minimize cardiovascular impairment
What are 2 types of respiratory failure?
Hypoxemic respiratory failure
Hypecapnic respiratory failure
What value is affected to be classified as hypoxemic respiratory failure?
PaO2 < 60mmHg on room air.
What values change to be classified as Hypercapnic respiratory failure?
PaCO2 > 45 mmHg
pH < 7.35
Also known as respiratory acidosis
when hypoxemic respiratory failure results in a normal (A-a) gradient; what is the usual cause?
decreased PiO2 or Hypoventilation
An increased (A-a) gradient will result when the hypoxemia is due to which defects/conditions?
True shunt
V/Q mismatch
Diffusion defects
What are classic indications for mechanical ventilation? (4)
- Apnea
- Acute ventilatory failure
- Impending ventilatory failure
- Severe refractory hypoxemia
What are signs of impending ventilatory failure?
WOB
Muscle strength and lung expansion critical numbers
What are common causes of hypoxemic failure?
V/Q mismatch
shunt
alveolar hypoventilation
diffusion impairment
decreased inspired FiO2
Causes of Apnea
Arrests
sedation (o.d)
paralytic drugs
high c-spine injury
head injury/trauma
Signs of impending vent. failure?
air hunger
tachypneic
diaphoretic
WOB
Neuromuscular failure
guilluain-barre
MS
refractory failure can be inferred by what factors?
an increase in PaO2 of less than 10mmHg after an FiO2 increase of 0.20 (or more)
OR
PaO2 < 60 of an FiO2 of > 0.40
slide 7 (mod 5 - A)
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Critical numbers indicating inadequate alveolar ventilation
(i.e needs mech. ventilation)
PaCO2 > 55mmHg
pH < 7.25 (or 7.20)
BOTH must be met to indicate mechanical ventilatory support.
mechanisms for increased PaCO2 when there is inadequate alveolar ventilation.
Increased deadspace
Increased CO2 production
Decreased alveolar ventilation (Va)
Critical numbers indicating inadequate lung expansion
(i.e needs mech. ventilation)
Tidal volume < 5 mL/kg
Respiratory rate > 35 bpm
Vital capacity < 10 mL/kg
Small volumes result in inadequate lung expansion; what are they complications and predicted outcomes if this is the case?
Complications: atelecasis and impaired gas exchange
result in increased RR to maintain Ve (minute ventilation)
Higher respiratory rates correspond to what?
lower volumes.
Can lead to respiratory muscle fatigue
what is vital capacity?
The volume of air exhaled after a maximal inspiration
why is vital capacity a important value when determining whether or not a patient needs mechanical ventilation?
Vital capacity indicates both muscle strength and lung expansion ability;
TLDR; reflects the ability to cough and clear the airway.
How much vital capacity is needed for an adequate cough?
2 x tidal volume (Vt)
How do you measure vital capacity?
typically with a wrights (turbine) or bedside spirometer.
which patients would test vital capacity for?
those with progressive muscle weakness.
(ALS, GBS, MG etc.)
Critical numbers that indicate inadequate muscle strength
(i.e needs mech. ventilation)
-Max inspiratory pressure (MIP) greater than or equal to -20 cmH2O
-Max expiratory pressure (MEP) less than 40 cmH2O
-vital capacity < 10 mL/kg
-max voluntary ventilation < (2 x Ve)
Normal tidal volume?
5 - 8 mL/kg
Normal vital capacity?
65 - 75 mL/kg
Normal max inspiratory pressure (MIP)
what is it a measure of?
-80 to -100 cmH2O
Measures patients muscle strength
How do you measure max inspiratory pressure (MIP)?
who would it be done for?
Uses nose plugs; a pressure gauge, and a one-way valve that allows for exhalation only.
patients with progressive neuromuscular disorders
(i.e MG, GBS, ALS)
Normal Max expiratory pressure (MEP)
Normal > 100cmH2O
How do you calculate minute ventilation (MV) and what is a normal range?
MV = RR x Vt
Normal = 5-6 lpm
Critical value for WOB
(i.e needs mech. ventilation)
Minute ventilation [MV (or Ve)] > 10 LPM
Deadspace to tidal volume ratio (Vd/Vt) > 0.60
what are complications with minute ventilation in relation to WOB?
edit
Ve needed to maintain a stable PaCO2 may become so high that it can’t be reached by the patient.
at > 10 LPM; increased probability of respriatory failure developing 2 degrees to muscle fatigue
Normal deadspace to tidal volume ratio (Vd/Vt)
0.25 - 0.40 (25 - 40 %)
It takes work to move the air in and out of deadspace.
Why does Deadspace increases WOB
to maintain alveolar ventilation; which is also increased
For a given PaCO2, what variables increase/decrease to maintain PaCO2?
Deadspace (Vd) and minute ventilation (Ve)
M5 slide 17 (left off)
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What is continuous mandatory ventilation (CMV)?
Every breath is controlled by the ventilator
-may be vent. initiated (mandatory)
-may be patient initiated (assisted)
-vent. does all the WOB after initiated.
FULL vent. support.
Define intermittent mandatory ventilation (IMV)
Goal is to only deliver set # of mandatory breaths
-all breaths delivered above set rate are spontaneous
what is continuous spontaneous ventilation (CSV)?
breaths may be supported or unsupported by the ventilator
What is the main difference in trigger variable for assisted vs. mandatory breaths?
Assisted breath: patient begins inspiration but the ventilator controls inspiratory phase and ends inspiration.
Mandatory breaths are triggered only by time.
What are spontaneous breaths?
breaths that are triggered and cycled by the patient.
it can be supported or non supported
Non-supported spontaneous breaths: can be defined as?
Breaths that are triggered, limited, and cycled by the patient (vent does nothing)
The vent controls the baseline only; all phases except the baseline are controlled by the patient
Define supported spontaneous breaths
Breaths that are triggered and cycled by the patient, but limit and baseline are controlled by the vent.
Amount of Vent support determines WOB the patient must do
Ventilators: control system - phase variables
Triggers: Time, Flow, Pressure
Limit: Pressure, Volume, Flow
Cycle: pressure, volume, flow, time
Baseline
Ventilators: What is a Time triggered variable?
Controlled or mandatory breaths.
Breath is delivered after an amount of time has passed.
-breath is mandatory because vents start it.
need a RR to get a time trigger
Ventilators : A/C refers to what?
breaths are either assisted or controlled.
-patient triggered or time triggered.
What is an advantage of assist/control (CMV) ventilation?
If patient doesn’t trigger the breath, there is backup of time triggered breaths.
Ventilators: What does max sensitivity mean?
Ease for patient to trigger a breath.
Ventilators :What is a limit variable?
a variable that can reach/maintain a parameter before inspiration ends but does not terminate inspiration
What are the 3 limit variables for Ventilators?
Pressure
Volume
Flow
Ventilators: 2 ways to Pressure limit inspiration?
When looking at a Ventilator, what are the 3 graphs displaying?
In descending order:
Pressure (cmH2O)
Flow (L/m)
Volume (mL)
What is PEEP?
Positive End-Expiratory Pressure:
Keeps airway pressure above atmospheric throughout breathing cycle.
What are the advantages of PEEP?
PEEP maintains a patients FRC and can help improve oxygenation.
-referred to as CPAP when using w/spontaneous breathes
What is VC-CMV?
What is the Trigger, limit, cycle, and baseline?
edit
add slide 56
Volume controlled; continuous mechanical ventilation
How could you go about increasing lung volumes on a ventilator?
End-inspiration
End-expiration
FRC
What affects can mechanical ventilation have on cardiac function?
Can reduce myocardial demand secondary to hypoxemia and increased WOB
what factors increase PIP?
Anything that increases Pr or Pc
Does Pplat have a direct or indirect relationship with Volume & PEEP?
Direct
Does Pplat have a direct or indirect relationship with compliance?
Inverse
Variable relationships:
If you have [I] time and Vt; what can you calculate?
Flow
[I]time = Vt / Flow (Litres per second)
Variable relationships:
What variable does RR affect?
Expiration time;
Explanation:
TCT = 60/RR –> TCT = I + E
TCT = Time cycled between breaths
What is Flow?
How fast gas/fluids are moving
Measurement:
Liters per minute
Positive airway devices: how do you increase pressure?
Increase flow = Increase pressure
What happens to CO2 when RR increases?
It decreases; you blow off CO2
When would you not want to increase RR given a high CO2?
When pH is still normal; Pt could have a abnormal normal
chronic condition; i.e emphysema or COPD are compensated by HCO3 so its normal.
In volume control; how would you decrease inspiratory time?
Increasing flow; air is delivered faster.
Will a decreased PiO2 result in a decreased or increased [A-a] gradient?
normal A-a
When would hypoxemic resp. failure result in a normal A-a gradient?
When it is due to a decreased PiO2 and Hypoventilation
Hypoxemic resp. failure will result in a high or low PaO2?
Low
Hypoxemic resp. failure will result in a high or low PaCO3?q
Normal to Low
Hypoxemic resp. failure will result in a high or low P(A-a)O2?
high or normal
(normal if decreased PiO2 or hypoventilation)
Hypercapnic resp. failure will result in a low or high PaO2?
Low
Hypercapnic resp. failure will result in a low or high PaCO2?
High
Hypercapnic resp. failure will result in a high or low P(A-a)O2?
Normal
Combined Type I and II resp. failure result in a high or low PaO2?
Low
Combined Type I and II resp. failure result in a high or low PaCO2
High
Combined Type I and II resp. failure result in a high or low P(A-a)O2?
High
When the vital capacity [VC] is below 15-20, what does it indicate?
A lack of muscle strength and lung expansion to produce a adequate cough.
How do you know if someone doesn’t have an adequate cough based on vital capacity?
VC < 15-20 mL/kg
VC of 2 x Vt is needed for an adequate cough
A normal MV is what? and when are we concenred?
Normal = 5-6 Lpm
Critical > 10LPM
What is a normal MIP? and when are we concerned?
-80 to -100 cmH2O
Critical >= -20 cmH2O
What does MIP measure?
Pt’s muscle strength
What is a normal MEP? and when are we concerned?
Normal > 100 cmH2O
Critical < 40cmH2O
Any circuit distal to the WYE is added what?
Mech. deadspace
What is the point of heated wires in vent. circuits?
(2)
Prevents rainout
Prevent condensation
Why are water traps on some ventilators?
To collect rainout
True or False:
Frequently changing the circuit is a good way to prevent contamination and decrease the risk of vat?
False.
There is an increased risk of VAP with frequnet circuit changes
(no more than q7d)
