Mechanical Ventilation

Question 1

What are the goals of mechanical venilation?

Answer 1

• Improve ventilation
• Improve oxygenation

Question 2

What are common indications for mechanical ventilation

Answer 2

• Failure to maintain/protect airway
• Failure to ventilate/oxygenate
• Anticipation of need based on clinical course/likely deterioration

Question 3

Define compliance

Answer 3

• Amount of work required to inflate the lungs (i.e. stretch)

Question 4

Define resistance

Answer 4

• Amount of work required to move air through the lungs (i.e. airway diameter)

Question 5

Define elasticity

Answer 5

• Ability of lungs to recoil and expand

Question 6

Define deadspace

Answer 6

• Inhaled air that does not take part in gas exchange

Question 7

Define FiO2

Answer 7

• O2 concentration of air

Question 8

Define I:E

Answer 8

Inspiratory/Expiratory ratio
- Inspiratory Time compared to expiratory time

IE TE = total cycle time

Question 9

Define tidal volume

Answer 9

• Volume of gas moved in/out of lungs in single inspiration (VTI) or expiration (VTE)

Question 10

What is tidal volume roughly equal to?

Answer 10

6-8mLs/kg

Question 11

Define expired minute volume

Answer 11

• Total volume of gas moved out of the lungs in a minute

Question 12

Define rate

Answer 12

• Mandatory breaths to be delivered in a minute

Question 13

Define total rate

Answer 13

(fTotal)
- Total breaths taken in a minute
= rate + spontaneous breaths

Question 14

Define flow trigger

Answer 14

• Inspiratory flow in L/min that triggers ventilator to deliver a breath

Question 15

Define expiratory trigger sensitivity (ETS)

Answer 15

• % of peak inspiratory flow that triggers ventilator to cycle from inspiration to exhalation

Question 16

Define peak airway pressure (Ppeak)

Answer 16

• Highest pressure reached during last breath
  (affected by airway resistance and compliance)

Question 17

Define Pressure control (Pcontrol)

Answer 17

Amount of pressure applied during inspiration in addition to PEEP

Question 18

Define Pressure support (Psupport)

Answer 18

Amount of pressure delivered to support spontaneous breaths

Question 19

What does VC SIMV+ stand for

Answer 19

Volume Controlled Synchronised Intermittent Mandatory Ventilation

Question 20

How does VC SIMV+ work

Answer 20

• Ventilator delivers a set tidal volume at specific rate and supports patient’s own breathing
• Ventilator detects patient’s spontaneous breath and either augments this and synchronises it with the pre-set breath OR supports breath with pre-set pressure support

Question 21

What does PC SIMV+ stand for?

Answer 21

Pressure Controlled Synchronised Intermittent Mandatory Ventilation

Question 22

How does PC SIMV+ work

Answer 22

• Pressure and rate are set
• Patient determines their own tidal volume to reach pre-set pressure target and can take spontaneous breaths

Question 23

What are the benefits of VC SIMV+

Answer 23

• Less change of respiratory muscle atrophy as patient can self-ventilate
• Level of sedation can be lower
• Less haemodynamic compromise as lower pressures are used
• Decreased risk of barotrauma

Question 24

What are the benefits of PC SIMV+

Answer 24

• Reduces risk of barotrauma
• Compensates for air leak when using uncuffed ETT tube (such as in paeds)
• Can be used with patients requiring higher airway pressures (i.e. non-complaint lungs ARDS, chronic lung diseases)