Pressure-Volume & Flow-Volume Loops

Question 0

Simple changes to what 3 things can create discrepancies between set and delivered TVs?

Answer 0

1. Fresh gas flow (FGF)
2. Respiratory rate (RR)
3. I:E ratio

Question 1

Compliance of the breathing circuit: For every 1 cm H20 pressure in the circuit ______ ml of volume is lost per breath r/t tubing distention and compressible volume.

Answer 1

2-8 ml

Question 2

The greatest TV augmentation occurs at the ….?

Answer 2

• Highest FGF (10L/min)
• Highest I:E (1:1)
• lowest RR (8)

Question 3

The lowest TV augmentation occurs at the …?

Answer 3

• Lowest FGF (0.25 L/min)
• Lowest I:E (1:3)
• Highest RR (16)

Question 4

The magnitude of delivered TV augmentation is ____________?

Answer 4

• Independent of the volume control TV setting

* Thus, the percent increase is much larger for pediatric settings

Question 5

What 2 methods increase TV accuracy?

Answer 5

1. Fresh gas decoupling

2. Fresh gas compensation

Question 6

What is fresh gas decoupling?

Answer 6

• Fresh gas is diverted by a decoupling valve to the manual breathing bag, and is thus not added to the delivered tidal volume.
• This helps ensure that the set and delivered tidal volumes are equal.

Question 7

What is fresh gas compensation (volume/flow sensors)?

Answer 7

The volume and flow sensors provide feedback which allows the ventilator to adjust the delivered tidal volume so that it matches the set tidal volume in spite of changes in the total fresh gas flow.

Question 8

How is MV (Minute Ventilation) calculated?

Answer 8

MV = RR x TV

Question 9

A pause at the end of inspiration is a ventilator option to…?

Answer 9

• Benefit alveolar gas distribution from the compliant to the less-complaint alveoli while maintenance of lower airway pressures.

Question 10

What is the usual I:E ratio?

Answer 10

1:2

Question 11

Longer inspiratory times generally improve oxygenation by:______?

Answer 11

1. Increases the mean airway pressure (longer period of high pressure increases mean airway pressure over entire respiratory cycle)
2. Allows re-distribution of gas from more compliant alveoli to less compliant alveoli

Question 12

What are the disadvantages of longer inspiratory times?

Answer 12

1. Increases the risk of gas trapping, intrinsic PEEP, and barotrauma by reducing expiratory time
2. Less well tolerated by the patient - requires deeper sedation levels
3. Decreases peak pressure by decreasing inspiratory flow

Question 13

What is compliance?

Answer 13

• change in volume/change in pressure
• measurement (ml/cmH2O) of how well the lung-thoracic system can change its total volume as changing pressure is applied

Question 14

Compliance = ?

Answer 14

• Expiratory TV / (pressure at the end of inspiration - pressure at the end of expiration)

Question 15

What is normal adult compliance?

Answer 15

35-100 ml/cmH2O

Question 16

What is normal pediatric compliance?

Answer 16

> 15 ml/cmH2O

Question 17

Compliance can easily be viewed via ___________?

Answer 17

Pressure-Volume Loops

Question 18

How will decreased compliance be represented on pressure-volume loops?

Answer 18

• The slope of the pressure-volume loop will move toward the horizontal/x-axis (more pressure is required to fill the lungs to a given volume)

Question 19

How will increased compliance be represented on pressure-volume loops?

Answer 19

The slope of the pressure-volume loop will move towards the vertical/y-axis (less pressure is required to fill the lungs to a given volume)

Question 20

What is resistance (Raw)?

Answer 20

• The relationship between the pressure difference across the airway (between the mouth and the alveoli) and the rate at which gas flows through the airway

Question 21

What is the most probable reason for a non-closing loop on the Flow-Volume Loop?

Answer 21

Leak

Question 22

On a Pressure-Volume Loop, spontaneous ventilation is represented how?

Answer 22

• negative pressure

Question 23

What do pressure-volume loops provide?

Answer 23

• information on dynamic trends of respiratory compliance

Question 24

What do flow-volume loops provide?

Answer 24

- information on dynamic trends of respiratory resistance

Question 25

Pressure-Volume Compliance Loop: Static?

Answer 25

- ICU vents can provide rapid airway occlusion at end-inspiration. During the pause, flow rapidly drops to zero and TV is briefly trapped inside the lung, at this point static airway pressure can be measured. - Absence of flow equals alveolar pressure, which reflects the elastic retraction of the entire respiratory system

Question 26

Pressure-volume compliance loop: Quasi-static?

Answer 26

- Obtained when inspiratory pause is shorter than 2 seconds & does not always reflect alveolar pressure

Question 27

Pressure-volume compliance loop: Dynamic?

Answer 27

- Obtained without flow interruption

Question 28

What is static compliance?

Answer 28

- Mirrors the elastic features of the respiratory system | - Only affected by variations in volume and/or complaince

Question 29

What is dynamic compliance?

Answer 29

- Provides information on both elastic & resistive (flow-dependent) components of the airways and endotracheal tube - Affected by variations in volume, compliance, airway secretions, bronchospasm, diameter of OET

Question 30

Plateau pressures greater than _____ cm H2O are associated with shear lung damage.

Answer 30

35

Question 31

What is normal lung and chest compliance?

Answer 31

50-80 ml/cm H2O

Question 32

What are the advantages of PEEP?

Answer 32

- Improved PaO2 - Reduces right --> left intrapulmonary shunting (PEEP expands collapsed, but perfused alveoli) - Increases FRC through maximal alveolar recruitment - Prevents airway & alveolar closure at end-expiration

Question 33

What are disadvantages of PEEP?

Answer 33

- Excessive distention of alveoli may cause compression of pulmonary vasculature * decreased preload * increased CVP * increased risk for barotrauma * redistribution of pulmonary blood flow * promotion of pulmonary edema-impeding lymphatic drainage from lungs

Question 34

What is "Best" PEEP?

Answer 34

- level of PEEP that produces maximal PaO2 with an FiO2 less than or equal to 0.5 with the least decrement in CO and over distention of alveoli