Ventilation

Question 1

Aim of ventilation:

Answer 1

• To allow gas exchange to happen  want to give oxygen to patient & take away carbon dioxide
• We want to generate flow & volume to provide adequate alveolar ventilation & to allow for effective gaseous exchange

Question 2

Negative pressure ventilation

Answer 2

patient is breathing spontaneously

Question 2

When ventilation is needed

Answer 2

• When there is respiratory depression because of the anaesthetic and the analgesia
• To facilitate surgery
• Any patient who has received a muscle relaxant must always be ventilated!
• Any open cavity surgery
• Patients with respiratory disease who have poor underlying lung function / associated diseases

Question 3

Positive pressure ventilation

Answer 3

we are providing ventilation for the patient
Exhalation still occurs passively  we take away the positive pressure and then the gradient reverses itself

Question 4

PEEP = positive end expiratory pressure. What is it’s aim?

Answer 4

provides positive pressure at the end of expiration
Aim of peep is to prevent atelectasis
> improved FRC and improved
gas exchange. Keeps lungs open.

**NB Go look at these breathing curves

On the pressure graph, you can see that the line doesn’t go back to
the baseline with expiration because we are providing positive
pressure

Question 5

CPAP > continuous positive airway pressure:

Answer 5

• PEEP is only applied at the end of expiration, whereas CPAP is applied throughout respiration (I+E)
• We usually use it for patients who are breathing spontaneously & often in patients who have some degree of upper airway obstruction  CPAP will open the airway & allow the patient to ventilate themselves
• Can be used in the emergency setting when there isn’t an ET tube or LMA available
• It is part of the treatment for laryngospasm (with suxamethonium)

Question 6

Compare CPAP with PEEP

Answer 6

CPAP
1. Spontaneously breathing pt
2. To counter upper air obstruction
3. Inspiration & Expiration

PEEP
1. Intubated & Ventilated pts
2. To splint alveoli open
3. Expiration only

Question 7

CPAP and PEEP both do the following:

Answer 7

• Improve lung compliance
• Improve gas exchange
• Reduce venous return
• May decrease the cardiac output

Question 8

Controlled mechanical ventilation / intermittent positive pressure ventilation (IPPV)

Answer 8

we are doing the breathing for the patient
**NB NB go look at these curves

Question 9

Volume controlled vs pressure controlled ventilation

Answer 9

Vol controlled: as the ventilation starts giving the set tidal volume, it will reach a certain peak pressure, and then you expire. It will give that tidal volume by force if it needs to & this can be harmful for patients

Pressure controlled: you are setting the pressure and then the machine achieves that pressure & holds that pressure for a set time period before allowing exhalation. pressure-controlled = plateau on graph. Once pressure reached expiration will occur passively. Tidal volume here varies though. Stiff lungs will get to the pressure quickly with a low tidal vol

Question 10

SIMV > synchronised intermittent mandatory ventilation:

Answer 10

intermittent mandatory ventilation that attempts to synchronise with the patient
In a patient who is breathing spontaneously (indicated by the negative pressure created in the chest), the machine will give one breath in response to the patient’s attempt to breathe
Negative pressure on the graph indicates spontaneous breathing.

time window / threshold during which the patient needs to breathe.

Question 11

PSV > pressure support ventilation:

Answer 11

the patient triggers the ventilator, and then we give them a certain amount of pressure to assist with breathing
This is often used towards the end of anaesthesia when trying to get the patient to start breathing.
Plateau thus pressure support ventilation

Question 12

NIV > non-invasive ventilation:

Answer 12

ventilation that is given via a mask (usually to patients with respiratory disease) as a bridge to avoid intubation

Question 13

Lung-protective ventilation

Answer 13

We need to attempt to limit the pressure changes that the lung experiences. The lungs aren’t used to being ventilated / having those pressure changes, so harmful mediators get released in response to this > inflammatory mediators are released which may cause MODS.

• Avoid barotrauma > limit the driving pressure (limit the pressure changes that the lung experiences)
• Avoid atelectrauma > PEEP
• Avoid volutrauma > limit volume

Question 14

Hazards of giving too much oxygen:

Answer 14

• Absorption atelectasis
• Hypoventilation (COAD)
• Pulmonary toxicity
• Oxygen free radical formation
• Retinopathy of prematurity  preterm neonates