Mechanical Ventilation - Basics

Question 1

What determines the pressure required to push a flow of gas through a tube?

Answer 1

Resistance
Flow rate

Question 2

What determines the pressure required to inflate a balloon?

Answer 2

Volume
Compliance

Volume/compliance

Question 3

What is the formula for the pressure required to inflate the lung?

Answer 3

(Flow x resistance) + (volume/compliance)

Question 4

What is the formula for the AIRWAY pressure required to inflate the lungs?

Answer 4

Inflation pressure plus baseline pressure of the balloon.

Therefore

(Flow x resistance) + (volume / compliance) + PEEP

Question 5

Of these variables, which can be set independently?

Pressure, flow, volume

Answer 5

These three variables are dependent on one another.

Therefore, only two can be independently changed. The third will change in response

Question 6

How do you increase oxygenation by changing parameters on a ventilator?

Answer 6

You can:
- increase FiO2

Or, you can reduce shunt by:
- increasing PEEP
- Or increasing inspiratory time

Question 7

How do you increase CO2 removal by changing parameters on a ventilator?

Answer 7

Increase respiratory rate

Or

Increase tidal volumes

Question 8

What is a normal inspiratory to expiratory time ratio?

Answer 8

1:2

Or 30%

Question 9

Three complications if mechanical ventilation

Answer 9

Nosocomial pneumonia
Gas trapping
Ventilator-associated lung injury

Question 10

What can cause gas trapping?

Answer 10

High respiratory rates

Long inspiratory times (and therefore short expiratory times)

Large tidal volumes

Plus:
- Asthma
- COPD

Question 11

What can you do on a ventilator to measure total PEEP?

Answer 11

Press the inspiratory hold button and allow the pressures to equilibrate.

Then measure airway pressure

Question 12

Why does mechanical ventilation affect cardiac preload?

Answer 12

Normally venous return is enhanced by negative intrathoracic pressure produced on inspiration.

Positive pressure ventilation has the opposite effect.

Question 13

What effect does mechanical ventilation have on afterload?

Answer 13

Afterload is the tension in the left ventricular wall during systole.

Mechanical ventilation decreases afterload by reducing transmural pressure

Question 14

What is the overall effect of mechanical ventilation on cardiac output?

Answer 14

Decreasing preload and decreasing afterload have opposite effects on cardiac output.

Therefore, the overall effect can vary from patient to patient.

If their heart has reduced contractility by baseline, ventilation will increase output.

If their heart has normal contractility by baseline, ventilation will decrease output.

If they’re heart has