Anes Ventilators and Pulm Mgmt Flashcards
paralytics and a deepened anesthetic state cause what type of chest mvmts?
Uncoordinated/asynchronous chest movement
what type of ventilation is an unnatural process?
positive pressure ventilation
what 3 reasons are given as to why positive pressure ventilation is unnatural?
–Cyclic recruitment and de-recruitment of collapsed lung units
–Repetitive shear stress is shown to destroy cellular structures
–Inspiratory flow is directed to less resistant areas or areas qthat remain open resulting in overinflated alveoli
What 3 things happen to the lungs with anesthesia?
decrease in functional residual capacity
decrease in compliance
increased airway resistance
the loss of tone, reduced airway dimensions and smaller volumes result in what in the lungs?
airway closure and atelectasis
4 causes of ventilator-induced Lung Injury (VILI)
- volutrauma
- barotrauma
- atelectrauma
- biotrauma
Overdistention of alveoli
volutrauma
Excessive pulmonary pressures
Barotrauma
repeated opening and collapse of
atelectatic lung units
atelectrauma
nflammatory mediator release into
alveoli and surrounding bronchiole spaces (can be
caused by the 1st 3 traumas)
biotrauma
What is good for artificial positive pressure ventilation can be
detrimental to circulation and organ function because it:
- increases intrathoracic pressures and pvr
- cause distended lungs and cardiac septal shift
- decreased renal function from decreased CO
the Increased intrathoracic pressures and pulmonary vascular resistance causes what to happen in lungs?
Venous return (preload) is impeded decreased cardiac output
distended lungs and cardiac septal shift causes what in the lungs
- Alveolar distention may occur as well as air trapping
* Surfactant production may be impaired
Decreased cardiac output from pos pressure ventilation can lead to
decreased renal function, liver perfusion, low perfusion and ischemia to gastric mucosa
What causes the terminal bronchioles to collapse?
hyperinflated alveoli
what is the goal of protective mechanical ventilation?
to minimize injury to the lung
will large Vt and high fio2 prevent atelectasis?
NO
High FiO2 can accelerate atelectasis formation, does not help with gas exchange
what preserves lung mechanics
spontaneous ventilation
inspiration is terminated when
preset volume is reached.
Volume control:
inspiration is terminated when
preset pressure is reached.
Pressure control:
a change in volume for a given change in pressure
Compliance
when is compliance greater in the lung?
Compliance is higher at the beginning of inspiration because lungs are
empty, and the volume change is greater the given lower pressure
Low compliance results in
a smaller volume change for a given pressure change
High compliance results in
a larger volume change for a given pressure change
what determines how much time the respiratory cycle will last
respiratory rate
type of ventilator that will slow down flow as it nears the end of inspiration?
variable flow ventilator and is known as decelerating flow pattern
During inspiration a flow rate of 1 liter/ second
requires
2 cm H20 pressure
3 cm H20 pressure will distend lung to
500 cc
Occurs during times without gas flow, such as
during an inspiratory pause or at the end of
inhalation
Static Lung Compliance
Static Lung Compliance is measured by
plateau pressure which is mostly constant
what is the more accurate measure of compliance?
static compliance
Occurs during times of gas flow, during active
inspiration
Dynamic Lung Compliance
what does dynamic compliance measure?
lung compliance AND resistance
what contributes to a decrease in
dynamic compliance
airway resistance - it is measure by peak insp flow
Weight of ascending bellows adds
2-3
cmH20 PEEP
difference in descending bellows and ascending?
descending are not safe and ascend during
inspiration and descend during expiration so disconnect is not always caught
Initial Ventilator Settings
RR - 8-12 Vt - 6-8 ml/kg avoid high PiP >35-40 PEEP >4 cmh2o fio2 40-50% I:E 1:2
PEEP can decrease
venous return, CO, SBP but still USE IT
Circuit compliance (distensibility) =
5ml/cmH20
Gas sampling =
150 ml/min (2.5 ml/second)
Gas compression=
3%
what is the difference in set and delivered Vt?
basically, pt will not be getting Vt set because of loss from circuit compliance, gas sampling, and gas compression
goal of Vt?
keep alveoli open, expanded, recruited, control ETCO2
what do you want to keep Vt under?
10 ml/kg
safest way to ventilate?
low Vt and PEEP
most efficient way to ventilate?
Vt
Hypoventilation (↓ PAO2 /↑ PACO2) is common with
MAC anesthesia or when using an
LMA with spontaneous ventilating patient
Alveolar air equations
PAO2 = FiO2 x (760-47) – PACO2/0.8
what determines how fast the Vt is delivered
inspiratory flow
The higher the I:E ratio, the greater the
inspiratory time and the lower the inspiratory pressures
since the breath is delivered over a longer amount of time.
has been utilized to allow
longer inspiratory times under lower pressures in order for inspired volume to reach & recruit collapsed alveoli.
Inverse ratio ventilation(IVR)(ex:2:1)
Effect of I:E ratio on PiPs
the lower the ratio (1:4 vs 1:1.5), the higher the PiP because the Vt has to be delivered over a shorter period of time
I:E ratio reflects the
inspiratory time (time Vt is delivered) in relation to the expiratory time (end inspiration to start of next)
Effect of I:E ratio on ETCO2 with constant
tidal volume and rate
The longer you stay in expiratory phase, the more CO2 you can breathe out.
Ex: 1:2 to 1:4 - will spend more time breathing OUT and releasing CO2 with 1:4
Effect of I:E ratio on inspiratory flow and
pressure with constant Vt and rate
Pressure and flow will increase with a lower I:E ratio.
Ex: 1:2 vs 1:1 have a shorter time to get a tidal volume in at a ratio of 1:2 then at 1:1 because you are spending more time of the resp cycle in expiration phase
Laminar flow changes to turbulent flow when
- Critical velocity is reached
- Direction and/or diameter is changed
- Flow is obstructed or resistance increased
What leads to turbulent flow in lungs
bronchospasm
airway edema
mucous and secretions
Can adjusting the ventilator I:E ratio
lead to turbulent air flow?
Yes, the lower the ratio (1:4 vs 1:2) the higher the flow and pressure to get the tidal volume in during the inspiratory phase
Effect of rate on inspiratory flow and
pressure with constant I:E ratio
the lower the RR, the longer the resp cycle. The longer the resp cycle, the longer amount of time you have to get tidal volume into patient. Increasing the RR would increase inspiratory flow and pressure
Effect of increasing FGF on Vt and Vm
↑FGF = ↑Vt,↑ Vm and ↑ PiPs
FGF decoupling
(flow compensator) is used on most of the newer
anesthesia ventilators to combat the increase of flow from an increase in FGF
You are using a ventilator that only has rate and minute
ventilation. Turning the rate up and leaving the minute
ventilation unchanged will affect the tidal volume how?
the Vt will decrease because you are getting more breaths in per minute without changing the mV
Effects of rate and Vm adjustment on Vt in
ventilators with only Vm and rate controls
ex: Vm = 8000, rate 10 = Vt 800 mls
- If you lower the RR and do not change mV the Vt ↑
- If you lower mV and do not change RR, Vt will dec
- if you ↑ RR and do not change mV, Vt will decrease
Most common ventilation mode
•Advantages are that tidal volume is set and kept constant and delivered each breath
Volume controlled Ventilation (CMV or VCV)
Volume controlled Ventilation (CMV or VCV) is best for patients and why?
Best for patients with no respiratory effort and little expected change in airway resistance and intra-thoracic pressure bc you PiP is variable which could lead to barotrauma
How Inspiratory flow affects I:E ratio
increasing inspiratory flow decreases the I:E ratio because you are blowing the air in FASTER causing a decrease in the length of the inspiratory cycle
Tidal volume delivered is based on preset
pressure target being reached
Pressure Controlled Ventilation (PCV)
how are inspiratory times and tidal volumes effected with Pressure Controlled Ventilation (PCV)?
- Inspiratory times are longer
- Tidal volume can vary breath to breath
how are tidal volumes set with pressure controlled vent?
based on desired pressure
not volume so that peak airway pressure is
controlled.
NOT guaranteed
when does expiration occur during pcv?
when the inspiratory time and
airway pressures are reached.
Indications PCV?
•Useful when high PiPs are not appropriate:
–LMA, emphysema, neonates and children
•Useful when low compliance is present:
–Laparoscopy, pregnancy, morbid obesity, ARDS
what type of lung damage can happen?
volutrauma r/t an increase in Vt
Volume vs. Pressure Flow Patterns
volume = constant flow rate, will have flat line and look like a box pressure = decelerating flow pattern, will have a peak and then a slope downward
If you are using pressure
control ventilation and compliance changes
from low to high how will volume change?
your volume is going to increase r/t lungs being able to more easily expand
If you are using pressure
control ventilation and resistance changes
from low to high how will volume change?
lower resistance, higher volumes, increased resistance = lower volumes
Ventilator’s attempt to guarantee a set volume in a pressure-controlled mode of ventilation
VG = Volume Guarantee
how does pressure support ventilation work?
When patient’s effort reaches the set inspiratory flow
trigger (sensitivity) (≈ 2L/min) the pressure supported
breath is initiated and delivered throughout inspiration.
describe flow, RR, and inspiratory phase of pressure support vent
- When flow decreases expiration begins
- Only inspiratory pressure is set.
- Respiratory rate is determined by the patient.
Pressure Support Ventilation (PSV) indications:
•Designed to augment Vt in spontaneously
breathing patients.
•To decrease WOB & increase patient comfort
•Weak inspiratory effort
–Deep level of anesthetic
–Residual muscle paralysis
•Obstructed airway breathing
Senses negative pressure inside the chest cavity created by diaphragm and
knows the patient initiated a patient driven breath
Synchronized Intermittent Mandatory Ventilation (SIMV)
If patient does not inspire within trigger synchronization window waiting
time, what happens?
ventilator then will deliver a breath
Ensures enough mandatory breaths if patient’s breathing efforts fall
outside time frame of breath
Advantages of SIMV
more pt control of ventilations, backup for spontaneous breathing pt that may be too weak to stay normocarbic
AC
will deliver set breaths no matter what the pt does so could result in some serious lung trauma
