Mechanical Ventilation

Question 1

Bellows Ventilator

Answer 1

• pneumatically (gas) driven, electronically controlled
• pneumatic force compresses a bellows, which empties its contents (gas from flometers and vaporizer) into circuit

Question 2

Driving Gas

Answer 2

oxygen, air, or venturi mix of both (injector)

Question 3

Venturi Mechanism (injector)

Answer 3

gas flows through constricted area at high velocity, pressure around it drops below atmospheric pressure and air is entrained.

net result = increase in total gas flow leaving outlet

Question 4

Bellows Ventilator 2

Answer 4

• pneumatically (gas) driven
• inner and outer compartment
• driving gas enters outer compartment and depresses bellows
• inner compartment delivers gas to patient breathing circuit

Question 5

Movement of bellows is controlled by what?

Answer 5

• Movement is controlled by drive gas which enters outer chamber and pushes bellows containing circuit gas into breathing circuit.
• During exhalation the bellows fills w gas from breathing circuit and fresh gas from flow meters
• Excess gas and pressure is vented out to scavenging system via spill valve

Question 6

Why can drive gas go to atmosphere and not scavenging system?

Answer 6

Drive gas is not contaminated (oxygen and air to compress bellows) so it can go to atmosphere.

Question 7

Hanging/Descending Bellows

Answer 7

• weighted
• causes PEEP
• safety: if there is a leak the bellows will descend anyways (weighted) and entrain air

Question 8

Ascending Bellows

Answer 8

• filing is dependent on exhaled gases from tight circuit
• failure to rise if leak is > than FGF

Question 9

Piston Ventilator

Answer 9

• do NOT require driving gas!
• driven by electric motor (no electricity = no ventilation)
• computer determines how far piston needs to move to deliver set TV or pressure (more accurate than bellows)
• at end inspiration, piston retracts and cylinder is filled w fresh (from flometers) and exhaled gases that have passed through CO2 absorber

Question 10

2 Factors that May Effect Delivered TV

Answer 10

1. FGF
2. Compliance of circuit

Question 11

FGF

Answer 11

• changes in flow rate, I:E ratios, or RR can alter delivered volume
• modern machines adjust for this (FGF compensation, FG decoupling)

Question 12

Fresh Gas Decoupling

Answer 12

prevents FGF from entering the breathing system during inspiration so that FGF does not contribute to TV

Question 13

Compliance of Circuit

Answer 13

modern machines calculate for this and compensate for it

Question 14

Ventilator Modes: Mandatory Ventilation and Support Ventilation

Answer 14

Mandatory: VC and SIMV

Support: PSV

Question 15

Vent Settings

Answer 15

• PEEP
• RR
• I:E ratio
• Pressure
• Volume

Question 16

Normal TV

Answer 16

500-700 mL

Question 17

Normal Minute Ventilation

Answer 17

5-6 L/min

Question 18

Normal Setting for TV

Answer 18

7-10 mL/kg

Question 19

MV

Answer 19

TV x RR

ie: 500 TV at 6 breaths/min = MV of 3L /min

Question 20

Volume Control Ventilation - VCV

Answer 20

• most common (good for new CRNAs)
• you set TV and RR, peak pressure varies
• minute ventilation remains constant

Question 21

Pressure Control Ventilation - PCV

Answer 21

• you set peak pressure and RR, TV varies based on pt resistance and compliance
• MV will vary (because TV varies)
• you can underventilate the pt w this setting, but barotrauma is avoided because you’ll never overpressure them (supraglottic airway)

Question 22

PC vs VC

Answer 22

• square wave pattern in VCV results in higher peak pressure for same TV
• pressure control gets you better volume for your pressure but there is a greater risk of underventilating

Question 23

Pressure Control - Volume Guarantee - PCV-VG

Answer 23

• based on the fact that PC gives you better volume
• smart mode: you set desired TV and max pressure you will tolerate to get to that TV
• delivers preset TV w lowest pressure using decelerating flow pattern (like PC)
• pt’s compliance determined from 1st breath which is VC and inspiratory pressure is established for all subsequent breaths
• • VG ensures that for all mandatory breaths the set TV is applied w minimum pressure required*
• if resistance/compliance changes, pressure gradually adapts over several breaths to restore set TV

Question 24

Pressure Support Ventilation - PSV

Answer 24

• used for pts spontaneously breathing
• you set PS for machine to deliver during spont breathing
• once ventilator senses inspiratory effort from pt, it provides constant pressure to the airway to relieve WOB
• 2 different ways vent can sense spont breaths: pressure changes (negative pressure) or flow past fow sensor during exhaltion

Question 25

PSV-Pro (GE Healthcare Machines)

Answer 25

• back up ventilation in case pt stops breathing
• back up mode is SIMV-PC
• you set min mandatory RR and pressure
• in between mandatory breaths, pt receives pressure support

Question 26

Synchronized Intermittent Mandatory Ventilation (SIMV)

Answer 26

• combo of spont and mandatory ventilation
• machine breaths delivered in set intervals
• SIMV-VC: you set TV and RR
• SIMV-PC: you set pressure and RR

Question 27

VC vs PC Table

Answer 27

Question 28

Hazards

Answer 28

• electricity failure (powers BOTH vents)
• machines have 30 min backup
• gas supply lost on bellows (less gas required in piston because it doesn’t require drive gas)

Question 29

Incorrect Vent Settings

Answer 29

• know default on vent (500TV on baby = bad)
• check settings before induction
• can cause barotrauma, hypo or hyperventilation

Question 30

Alarm Failure

Answer 30

• know alarm settings and NEVER turn them off

Question 31

Schematic of hos gas flows through patient and to machine

Answer 31