W7: Ventilation

Question 1

What is PEEP?

Answer 1

Positive end expiratory pressure (PEEP)
PEEP, or Positive End-Expiratory Pressure, is a mode of mechanical ventilation used to help people with respiratory issues. When you breathe out, your lungs don’t empty completely; there’s always some air left in them. PEEP helps maintain a certain level of pressure in the airways at the end of exhalation to keep the alveoli (tiny air sacs in the lungs) open.

Question 2

Why is PEEP important? x4

Answer 2

Improves Gas Exchange: By keeping the alveoli open, PEEP allows for better oxygen and carbon dioxide exchange.

Prevents Alveolar Collapse: In diseases or conditions where the alveoli might collapse (atelectasis), PEEP helps keep them open, which prevents them from collapsing and promotes better lung function.

Reduces Work of Breathing: By keeping the alveoli open, the lungs are more effective at exchanging gases, which can reduce the effort needed to breathe.

Improves Lung Compliance: Compliance refers to how easily the lungs can expand and contract. PEEP can help improve lung compliance by keeping the lungs more inflated, which helps in easier breathing.

Question 3

What is low flow vs high flow oxygen systems?

Answer 3

• Low-flow systems provide lower oxygen flow than the actual inspiratory flow (∼30 L·min−1). When a patient breathes in, they draw in room air along with the supplemental oxygen
• High-flow systems deliver oxygen at a flow rate that is equal to or greater than the patient’s inspiratory flow rate. For instance, if the patient’s breathing rate is 30 L/min, the system might deliver oxygen at the same rate or higher.

Question 4

Are nasal prongs high/low flow?
What should the flow not exceed?
What is the max % of 02 they can deliver?

Answer 4

Low flow
4L
35-36%

Question 5

What is the concentration of 02 for a simple face mask/hudson mask?

It should never be used at flow rates of ….. Why?

Answer 5

Delivers concentrations of 35-65% depending on the patients respiratory and tidal volume

<6L. Rebreathing of C02 may occur (If it’s too low there is not enough air pushing out C02 )

Question 6

What concentration is a venturi mask ideal for?

Answer 6

Suited for patients who require 02 concentration between 24-50%. Fi02 is adjusted using the gas flow.

Question 7

What level of 02 does a rebreather mask deliver?

Answer 7

Delivers 90-100% 02 if there is not a leak in the system

Question 8

In what patients is NIV shown to be as effective as and better tolerated than intubation and mechanical ventilation?

Answer 8

COPD patients

Question 9

What does CPAP and BIPAP do?

Answer 9

Assists both the inspiratory and expiratory phases of breathing

BIPAP can actively assist respiration through augmentation of alveolar ventilation

Question 10

BIPAP
- Supports both ….
- How many pressures?
- What are they known as?

Answer 10

• Inspiratory and expiratory phases of spontaneous breathing
• 2 (Bi-level)
• IPAP (inspiratory positive airway pressure) & EPAP (expiratory positive airway pressure)

Question 11

BIPAP:
What does IPAP increase

What is EPAP? What is its purpose?

Answer 11

• IPAP increases the patient’s tidal volume and supports alveolar ventilation
• When exhalation commences a pressure is applied at end expiration (EPAP: expiratory positive airway pressure), otherwise known as PEEP – this is a lower pressure than IPAP that is provided throughout expiration
• EPAP increases functional residual capacity of the lungs and decreases airway closure. Areas of atelectasis can be re-expanded and fluid accumulation can be prevented /reduced. This aids in improved gas exchange and increase in arterial oxygen levels

Question 12

What is the difference between IPAP and EPAP?

Answer 12

The difference between IPAP and EPAP is commonly referred to as Pressure Support (PS).

Question 13

What is pressure support? BIPAP

Answer 13

IPAP - EPAP = PS. Pressure support is a preset amount of inspiratory pressure that augments the patient’s spontaneous inspiratory breath.

For example, if IPAP is 20 and EPAP is 10, then PS = 10. This support increases the amount of air the patient breathes in (tidal volume), helping them ventilate better and clear more CO2. The greater the pressure support, the larger the tidal volume.

Question 14

Simple explanation of pressure support?

Answer 14

Pressure support (PS) is like an extra boost given during inhalation.
When a patient takes a breath in, the machine adds extra pressure to make it easier for them to get air into their lungs.

In simple terms: PS helps make breathing less work for the patient. It supports their natural effort to breathe by pushing more air in, which helps them get a better breath and improve oxygen and CO2 exchange.

Question 15

What time of respiratory condition is BIPAP used?

How does BIPAP help minute ventilation?

Answer 15

• In type 2 respiratory failure (Low 02 & Pac02 > 45)

BiPAP can increase minute ventilation in two ways:

• Increasing Tidal Volume (TV): By providing pressure support (the difference between IPAP and EPAP), BiPAP helps the patient take deeper breaths, which increases the volume of air per breath.
• Increasing Respiratory Rate (RR): If the patient’s breathing rate is too slow, BiPAP can be set to give additional breaths, ensuring a higher rate of breathing.

So, BiPAP can help increase both TV and RR, which together boosts minute ventilation, leading to better oxygenation and CO2 clearance.

Question 16

How does airflow work in CPAP?

Answer 16

Air is being moved into the mask continuously regardless of whether the patient is inspiring or expiring

Question 17

How does the positive pressure in CPAP help improve lung compliance and decrease the WOB?

Answer 17

• Enabling the patient to take larger tidal volumes for the same amount of effort
• Increasing Functional Residual Capacity (FRC) i.e. preventing alveolar collapse and thereby increasing the surface area for oxygen exchange to occur
• Reducing ventilation/perfusion (V/Q) mismatch –> by restoring FRC by increasing baseline airway pressur

Question 18

When is CPAP used?

Answer 18

• CPAP is used when patients have type 1 respiratory failure resulting in low 02 (C02 is normal)
• Essentially its useful for those in hypoxemic respiratory failure (good option for CHF, increases intrathoracic pressure thereby decreasing preload, increasing CO, pressure inside the alveoli can help push the fluid out hence the congestion – really opening them up to gas exchange and most importantly recruit/open the alveoli to decrease WOB and provide more alveoli to be available for gas exchange

Question 19

Summary of CPAP purpose?

Answer 19

CPAP primarily works by keeping the airways open and ensuring that the alveoli (tiny air sacs in the lungs) remain inflated. This can improve ventilation and increase the surface area available for gas exchange, which can help with oxygenation indirectly.

Question 20

Outline the two methods through which invasive ventilation is provided?

Which method has less dead space?

Answer 20

• Endotracheal
• Short-medium term invasive ventilation (< 14 days)
• Sits 4cm above the carina

Tracheostomy
- When a patient needs to be ventilated for > 14 days (or to bypass an obstructed upper airway)
- Percutaneous tracheostomy or
Surgical tracheostomy
- This method has less dead space ventilation than an ET tube because its closer to the lungs

Question 21

Why is humidification required?

Answer 21

• Patients on mechanical ventilation are connected to wall air without any humidification – if you breath very dry air the secretions will start to dry out and the cilia will have issues functioning = sputum retention

Question 22

What is pressure support ventilation?

Answer 22

• PSV is a method of assisting spontaneous breathing in a ventilated patient
• Patients are weaned from SIMV to pressure support as soon as they are able to initiate spontaneous breaths and maintain adequate minute ventilation

Question 23

What aspects of breathing do patients on pressure support have control over?

Answer 23

Can control respiration rate and tidal volume

Question 24

Pressure support is active during what stage of breathing?

Answer 24

Inspiration

Question 25

In pressure support ventilation, the peak inspiratory pressure is equal to……

Answer 25

PS + PEEP

Question 26

How does pressure support ventilation work?

Answer 26

Once the ventilator detects the patient’s effort, it provides air at a set pressure, which is the “pressure support” (e.g., 10 cm H₂O as in your example). This pressure remains constant during the inspiratory phase.

Question 27

What is synchronised intermittent mandatory ventilation?

Answer 27

• When we breath in it creates a negative pressure
• The patients inspiratory effort (ie the negative pressure) triggers the ventilator to deliver a patient-initiated mandatory breath

Question 28

Distinguish between pressure support ventilation and synchronised intermitted mandatory ventilation?

Answer 28

Control of Breath: In PSV, all breaths are initiated and controlled by the patient with ventilator support to augment inspiration. In SIMV, the ventilator provides a combination of spontaneous breaths and mandatory breaths that can be controlled by the ventilator.

PSV provides pressure support to help the patient with their spontaneous breathing effort. SIMV provides both pressure support (for spontaneous breaths) and full control of the mandatory breaths.

Question 29

What are the three types of breaths delivered in SIMV?

Answer 29

Mandatory breath
Assisted breath
Spontaneous breath

Question 30

What is a mandatory breath SIMV?

Answer 30

if the patient doesn’t initiate sufficient inspiratory effort within the timing window, the mandatory SIMV breath is delivered at the scheduled time. The ventilator will then reset to respond to the next spontaneous inspiratory effort

Question 31

What is an assisted breath SIMV?

Answer 31

When a mandatory SIMV breath is due the assist or timing window opens and waits for the patients inspiratory effort. Upon sensing the patients inspiratory effort, the ventilator delivers the preset tidal volume or inspiratory pressure in synchrony with the patient. As soon as the mandatory breath has been triggered, the assist window closes

Question 32

What is a spontaneous breath SIMV?

Answer 32

In between these mandatory or assisted breaths, the patient may initiate spontaneous breaths in synchrony with the ventilator. The volume of the spontaneous breath is dependent on the respiratory muscular effort that the patient is able to generate, the level of pressure support set and resistance and compliance.

Question 33

What is controlled mechanical ventilation?

Answer 33

This mode delivers a preset number of breaths at a set volume or pressure, regardless of the patient’s efforts – the patient is unable to trigger the ventilator to take a spontaneous breath

Question 34

Who is CMV useful in?

Answer 34

CMV is useful in a relaxed / paralysed patients without muscle activity. Often used if a patient is unable to initiate breath or is paralysed.

Question 35

What is volume controlled ventilation (form of CMV)

Answer 35

Goal: Ensure that the patient gets a specific volume of air with each breath.

How it works: The machine delivers a set amount of air (tidal volume) to the lungs, no matter what.

Key points:
- The air volume is fixed for each breath, so the ventilator keeps pushing air until this set volume is reached.
- The pressure can change depending on how stiff the lungs are (lung compliance) or if there’s blockage in the airways.
- It’s useful when you want to control the exact amount of air a patient receives but need to monitor the pressure to avoid damage.

Class notes (AI simplified above)
* Fixed RR & Vt using a constant gas flow rate → volume dependent on inspiratory time
* Once the preset inspiratory time or tidal volume is reached inspiration ends and expiration will begin
* Conservative ventilation strategy Vt~6-8ml/kg (to prevent excessive lung stretch)
* Pressure limit can also be set
* I:E (inspiratory : expiratory time ratio)

Question 36

What is pressure controlled ventilation (form of CMV)?

Answer 36

Goal: Ensure that the patient gets air with a specific pressure with each breath.

How it works: The machine pushes air into the lungs until a certain pressure is reached, and then stops.

Key points:
- The pressure is fixed, but the amount of air (tidal volume) the patient gets depends on how easily the lungs expand (lung compliance) and the condition of the airways.
- It’s useful when you need to limit the pressure to prevent lung damage, but the volume of air delivered can vary depending on the patient’s lung condition.

Class notes (AI simplified above)

A volume of gas is delivered to the lungs at a constant pressure during a set inspiratory time

Once the inspiratory time is reached, inspiration ends and expiration will begin

Fixed RR (inspiratory time) & peak airway pressure

Question 37

When is pressure controlled ventilation used (form of controlled mechanical ventilation)

Answer 37

• Used in patients with poor lung compliance which exhibit high airway pressures and poor oxygenation while on volume controlled ventilation
• In these patients it is difficult to deliver adequate tidal volumes whilst limiting airway pressure to maintain a plateau pressure of < 30
• In PCV the clinician is able to gain control over airway pressures and prevent complications by predetermining the inspiratory pressure required by the patient to achieve ideal volumes and improve oxygenation

Question 38

Summary of controlled mechanical ventilation

• The ventilator performs all the …..
• Preset mandatory rate x …. …. or inspiratory pressure
• No ….. breathing
• An inspiratory effort by the patient ….. ….. produce a machine delivered breath
• The patient cannot …. the ventilator to take a spontaneous breath
• The patient should be ….. …… ….

Answer 38

WOB
Tidal volume
Spontaneous
Will not
Trigger
Sedated & paralysed

Question 39

What is assist control ventilation?

Answer 39

• Vt and RR are on a minimum setting (tidal volume and respiratory rate)
• Ventilator triggered breaths are time cycled
• Patients effort can trigger additional set CMV (controlled mandatory ventilation) breaths
• Flow-trigger
• Pressure sensitivity

**All breaths are assisted ie no spontaneous breaths

Two breaths = VIM = ventilator initiated mandatory & PIM = patient initiated mandatory

The little dip on a graph will indicate the drop in pressure which the ventilator recognises is the patient trying to inspire and then it delivers that patient initiated mandatory breath. The last one is a ventilator initiated mandatory breath because there is no dip ie no attempt from the patient, so the machine will just deliver that breath through a time cycle.

Question 40

PEEP of 10 and pressure support of 12, what is the maximum pressure the patient will get?

How does peep work?

Does peep minimise shunt or dead space?

Answer 40

• Maximum pressure the patient will get is 22
• That PEEP happens during the expiratory cycle it stops the alveoli from collapsing during expiration
• By keeping the airways and alveoli recruited or working – the alveoli stays open which minimises shunt or intra-pulmonary shunt (ie an area which has circulation or perfusion but no ventilation)
• Essentially having PEEP keeps the airway recruited so that way there is both ventilation and perfusion and reduced shunt

Question 41

What is manual hyperinflation?

Answer 41

• Manual hyperinflation using the bag can be used for patients who are mechanically ventilated. This can help with secretion clearance. Suctioning can also be performed to expectorate/clear the secretions.