Patient-Vent Asynchrony (Mod4)

Question 1

What is Asynchrony associated with?

Answer 1

• Increased length of mechanical ventilation
• Increased ICU and hospital length of stay
• An increased need for tracheostomy
• Increase in ICU and hospital mortality

Question 2

What are clinical changes that would cause asynchrony?

Answer 2

• Secretions, bronchospasm, and agitation
• Fever, hypoxemia, and hemodynamic compromise
• Artificial airway problems, leaky air pathologies, body position alterations , difficult drug admin, abdominal distension

Question 3

What risk does excessive lower airway secretion production have?

Answer 3

Increases risk of obstruction which:

1. Increases peak airway pressures during volume ventilation and…
2. Decrease tidal volume in pressure ventilation

Question 4

Why is assisted mechanical ventilation at a higher risk of asynchrony?

Answer 4

More variables to control

• vent has to meet neurologic output from resp center
• Dependent on some level of effort from the patient

Question 5

Why is volume ventilation more likely to cause asynchrony?

Answer 5

Volume vent controls volume, flow, and time. The patient determines pressure. PC only controls pressure and time.

Question 6

What mode has the most control over ventialtion?

Answer 6

Volume a/c

Question 7

In pressure support, is volume controlled?

Answer 7

No, only the pressure is controlled.

Question 8

Why is PAV and NAVA least likely to cause asynchrony?

Answer 8

PAV and NAVA don’t exert any control over the patient.

• They provide a proportional assist based on patient demand

Question 9

What is Flow Asynchrony?

Answer 9

When the flow from the vent does not match the flow demand of the patient

• Can occur in any mode of vent
• most common in volume ventilation

Question 10

Volume ventilation controls flow directly, how would pressure ventilation address flow?

Answer 10

Inspiratory pressure rise time or pressure slope control adjusts the rate at which flow increases from baseline to peak

Question 11

moderate to strong vent demands require how much peak flow?

Answer 11

60 L/min or greater

Question 12

What factor does flow have in volume ventilation?

Answer 12

Flow and peak flow is set, they determine the precise inspiratory time a selected tidal volume is delivered.

Question 13

How is flow asynchrony corrected in volume ventilation?

Answer 13

By increasing peak flow and decreasing inspiratory time

Question 14

How is flow asynchrony corrected in pressure ventilation?

Answer 14

Adjusting rise time

Question 15

5 types of trigger asynchrony?

Answer 15

1. Trigger delay
2. Missing Triggering
3. Double triggering
4. Auto triggering
5. Reverse triggering

Question 16

What is trigger delay?

Answer 16

Length of time between the beginning of neuro-inspiration and activation of the ventilator is excessive

• Should not exceed 100 milliseconds to avoid patient perception of the delay and an increase in ventilatory drive
• Inappropriate set sensitivity or when auto peep is insufficient causing mistriggers

Question 17

What is missed trigger asyronchy?

Answer 17

Patient is unable to trigger the ventilator with each inspiratory effort

Question 18

What id double triggering asynchrony?

Answer 18

Result of the patient’s ventilatory center wanting a larger breath or a longer inspiratory time than is set on the ventilator

• A consequence is that breaths may get stacked because pt can’t exhale between breaths

Question 19

What is auto triggering?

Answer 19

Seemingly automatic triggering of the ventilator without any patient inspiratory effort

Question 20

What is Reverse triggering?

Answer 20

A controlled mechanical breath results in simulation of the respiratory center triggering the subsequent breath

• This form of asynchrony occurs only during controlled ventilation
• usually found with ARDS w/controlled breaths

Question 21

What is cycle asynchrony?

Answer 21

When the vent ends the breath at a time different from when the pts respiratory center wants to end the breath

• More common in PC than VC
• Ti is either too long or short with asynchrony

Question 22

What are 2 forms of cycle asynchrony?

Answer 22

1. Asynchrony that results in an inappropriately long inspiratory time
2. Asynchrony that results in an inappropriately short inspiratory time

Question 23

What is mode asynchrony?

Answer 23

The selection of a mode of ventilation that is highly unlikely to meet a patient’s inspiratory demand

Question 24

How do you correct flow asynchrony?

Answer 24

• Change to decelerating flow
• Increase peak flow (>60 L/min)
• Match ventilator’s inspiratory time to patient’s inspiratory time
• Ensure that the airway pressure waveform is as similar as possible to
  the ideal airway pressure waveform during controlled volume ventilation
• Change to a pressure-targeted mode of ventilation

Question 25

When would you change a square waveform to a decelerating waveform?

Answer 25

when the patient’s ventilatory demand is high

• the patient can be doing a disproportionate amount of work if the ventilator is not set to meet the patient’s inspiratory demand.
• If the patient is triggering inspiration, we recommend a decelerating flow pattern, especially when a small VT is being delivered.

Question 26

What does changing from a square to a decelerating waveform do?

Answer 26

A decelerating flow pattern allows a high peak flow to be delivered but also ensures that the inspiratory time can be adequately set

• has little affect on sedated patients, depends on patients who trigger the vent (and their Ti and Vt)

Question 27

What is the purpose of rise time?

Answer 27

The purpose of rise time is to adjust the rate at which flow increases from baseline to peak

• should be set at a value that ensures adequate inspiratory gas flow (meeting or exceeding patient demand)
• A dog ear appears if demand on is not met (on the insp aka left portion)

Question 28

What does a slow or low rise time do?

Answer 28

Increases patients WOB

Question 29

What is the most common cause of missed triggers?

Answer 29

Auto peep

• Insp Triggers are below baseline
• 2 or more efforts on the flow will not show any triggers on the pressure waveform

Question 30

What usually causes auto peep?

Answer 30

Auto-PEEP is most commonly caused by dynamic airway obstruction.

• Also caused by an expiratory time that is too short (and inspiratory time that is too long)
• Or the delivery of excessive minute vent/Vt
• Insp Triggers are below baseline

Question 31

Why is dynamic airway obstruction a problem, and how is it related to auto peep?

Answer 31

Airway disease ruins the structural integrity of the airways = compromised.

• A loss of smooth muscle causes the airway diameter to change
  from inspiration to expiration.
• During expiration the elastic recoil of the lung and thorax causes these damaged airways to at least partially collapse and in some cases totally collapse, trapping gas behind the obstruction or limiting flow to the point that at end-exhalation there is gas in the lung periphery under pressure or the presence of auto-PEEP

Question 32

How do you reduce auto peep to prevent missed triggers (insp triggers are not reaching baseline)

Answer 32

Decrease MV and/or increase expiratory time

• in COPD applied peep is used to min effort needed to trigger the vent (raising PEEP to help patient trigger)
• In the presence of dynamic airway obstruction, the
  application of PEEP offsets the effect of auto-PEEP on missed triggering

Question 33

Techniques to minimize effects of auto peep?

Answer 33

Question 34

How can you correct trigger delay?

Answer 34

Question 35

How do you correct double trigger?

Answer 35

Question 36

What happens if Ti is excessive with cycle asynchrony?

Answer 36

Spike in pressure set above level

Question 37

What happens if Ti is too short with cycle asynchrony?

Answer 37

Double trigger will occur with each breath

Question 38

Dog ears at the end of a pressure waveform indicate what?

Answer 38

Ti set is too long; the ti setting should be decreased.

• Tiset is too high; Pt stopped inspiring.