Compliance and Resistance

Question 1

What does compliance and resistance affect?

Answer 1

Has affect on mechanical ventilation and spontaneous ventilation.
Affects patient’s tidal volume and respiratory rate

Question 2

What is compliance

Answer 2

Measurement of the lungs ability to stretch

Compliance = change in volume (Vt)/ change in pressure (Ppleateau - PEEP)

Question 3

In volume targeted ventilation what happens to pressure in regards to compliance

Answer 3

When compliance increases, pressure decreases. When compliance decreases pressure increases

Question 4

In pressure target ventilation what happens to the volume in the lung in regards to compliance

Answer 4

When compliance increases, volume increases. When compliance degreases, volume decreases.

Question 5

What decreases compliance?

Answer 5

Intrapulmonary: Pulmonary edema
Extrapulmonary: Hemothorax (blood in the pleural space)
Extrathroaxic: Peritoneal fluid (fluid in the abdominal cavity)

Question 6

Calculations for static compliance and dynamic compliance

Answer 6

Static compliance = Vt/ (Pplateau - PEEP)

Dynamic compliance = Vt/ (Ppeak - PEEP)

Question 7

Normal values for resistance and what would increase resistance

Answer 7

Normal values for resistance are: 
Spontaneous ventilation = 0.6-2.4 cmH2O/L/sec
Mechanical = 6 cmH2O/L/sec
Anything that narrows the airway will increase resistance.
- Mucosal edema
- Bronchospasm
- Retained secretions
- Small ETT

Question 8

What would happen to the ventilator pressure waveform if compliance decreased?

Answer 8

If compliance decreases it takes more pressure to deliver the same amount of volume so Ppleateau and Ppeak will increase

Question 9

What would happen to the ventilator pressure waveform if resistance increased?

Answer 9

If resistance increases it will only affect Ppeak. Pplateau there is flow therefore no pressure due to resistance. Ppeak there is flow so the pressure due to resistance increases.

Question 10

How can you quickly determine if the compliance or the resistance has changed?

Answer 10

You can determine whether compliance or resistance has changed by measuring changes in Pplateau. If no pressure change in Pplateau then pressure increase is caused by resistance.

Question 11

If using pressure targeted ventilation, what would happen to the tidal volume if compliance decreased?

Answer 11

Since we are using pressure target ventilation, pressure will remain constant. If compliance decreases and the lung is stiffer the tidal volume will decrease.

Question 12

If lung compliance stays the same, and you increase VT, what happens to:

• Pplateau
• Ppeak
• Ppeak – Pplateau?

Answer 12

Pplateau = increases
Ppeak = increases
Ppeak - Ppleateau = stays the same

Question 13

What is dynamic compliance and how can you determine it?

Answer 13

Dynamic compliance is a combination of compliance and resistance.
It is reflected in Ppeak
Perform an inspiratory pause to differentiate between compliance and resistance if Ppeak changes.

Question 14

What is the pressure volume loop

Answer 14

Compares pressure to volume during inspiration and expiration
If it is measured with no flow, the increased pressure is due to recruiting alveoli or air liquid forces in alveoli

Question 15

What is hysteresis

Answer 15

The difference between inspiratory and expiratory pressure curves is called hysteresis
During active ventilation it can be affect by flow and resistance