Mechanical Ventilation & Hyperinflation

Question 1

What are the 2 reasons why patients need mechanical ventilation?

Answer 1

Respiratory failure
- Type 1 or 2

Airway protection

• Intubation due to airway compromise (e.g. stridor)
• Drug-induced coma

Question 2

Why do patients with respiratory failure require mechanical ventilation?

Answer 2

1. Pump stops working
   - diaphragm, rib cage, nerves, muscles
   - due to injury/pain or neural defect (e.g. brainstem infarct)
2. Gas exchange surface compromised
   - needs high level of pressure to guarantee adequate O2 into bloodstream
   - e.g. pneumonia, inflammation

Question 3

What are the causes of respiratory failure?

Answer 3

• Opioid drug use
• Cervical spinal cord injury
• Surgery/general anaesthetic
• Rib fractures
• APO
• PE
• Post-op atelectasis
• Pneumonia

Question 4

What is the function of a ventilator?

Answer 4

Inspiratory phase

• Provides required tidal volume
• Unloads respiratory muscles
• Reduces WOB
• Allows for CO2 removal

Expiratory phase
- Passive but has PEEP at the end of it

Question 5

What is positive end expiratory pressure (PEEP)?

Answer 5

Baseline pressure maintained in the lungs at the end of each exhalation

Question 6

Why is PEEP important?

Answer 6

• Prevents alveolar collapse (increases FRC)
• Overcomes resistance of tubing
• Reduces WOB (increases alveolar compliance)
• Never wean below 5cm H2O
• Holds open airways, but doesn’t make you take a breath

Question 7

What is pressure support?

Answer 7

If a patient can start a tiny breath, a ventilator will recognise it & boost it to make it a decent size breath

Question 8

What is the difference between pressure support & controlled ventilation?

Answer 8

• Support: Patient is in charge of starting the breath

- Controlled: Ventilator is in charge of starting the breath

Question 9

How does pressure support mode work?

Answer 9

• Baseline PEEP
• Recognises start of a breath
• Boosts each spontaneous breath to pre-set pressure

Question 10

What are the benefits of pressure support?

Answer 10

• Comfortable for patient

- Reduces WOB

Question 11

What are the two delivery modes of controlled mandatory ventilation (CMV)?

Answer 11

• Pressure controlled: Delivers set number of breaths to pre-set pressure
• Volume controlled: Delivers set number of breaths to pre-set volume
• Both ignore patient effort

Question 12

Why is CMV not commonly used?

Answer 12

• Patients require sedation/paralysis

- If patient wakes up it’s not comfortable or appropriate

Question 13

What is synchronised intermittent mandatory ventilation (SIMV)?

Answer 13

• Recognises patient effort (no breath-stacking)
• Gives controlled breaths as a minimum (even if no patient effort)
• Guarantees ventilation
• If patient starts spontaneous breathing, recognises these & behaves like pressure support

Question 14

What are the benefits of SIMV?

Answer 14

• Much more comfortable for patients who have any degree of alertness
• Good choice for transitional patients (e.g. waking from anaesthetic)
• Insurance policy: Will breathe even with no patient effort

Question 15

What are the other less commonly used modes of ventilation?

Answer 15

• Pressure control inverse ratio ventilation
• Airway pressure release ventilation (APRV)
• BiLevel ventilation
• High frequency/oscillation ventilation

Question 16

What is the meaning of the following terms:

• PIP
• ETCO2
• Vt
• Tinsp
• MV

Answer 16

• PIP: Peak inspiratory pressure (PEEP + PS)
• ETCO2: End-tidal CO2
• Vt: Tidal volume
• Tinsp: Inspiratory time (s)
• MV: Minute ventilation (RR x Vt)

Question 17

What role do physios have in ventilation?

Answer 17

• Pre-oxygenate prior to suction: 180s of 100% oxygen, then reverts to pre-set FiO2
• Coach deep breaths (ventilator provides feedback)
• Switch from one mode to another or increase PEEP (with medical permission)
• Perform ventilator hyperinflation (VHI)
• Put ventilator in stand-by mode (turn it off)
• Measure inspiratory muscle strength

Question 18

What are the complications of mechanical ventilation?

Answer 18

• Impaired V/Q matching
• Reduced surfactant production: Decreases sigh breaths, increases risk of atelectasis
• Reduced FRC: increases risk of atelectasis
• Impaired MC clearance: Drying effects, frequent atelectasis, high risk of pneumonia

Question 19

Why is impaired V/Q matching a complication of mechanical ventilation?

Answer 19

• Positive pressure: Ventilation goes to path of least resistance = airways already open (usually uppermost or non-dependent lung areas)
• Opposite of spontaneous breathing
• Increases risk of atelectasis in dependent regions

Question 20

What do the mechanical ventilation complications often lead to?

Answer 20

• Atelectasis/collapse

- Difficulty clearing sputum

Question 21

What are invasively ventilated patients unable to do?

Answer 21

• Truly cough/huff (ETT/trache prevents closure of glottis)
• Expectorate sputum easily (dependent on suction)
• Participate in PEP therapy

Question 22

What are some of the things that patients who are awake and invasively ventilated may be able to do?

Answer 22

• Take deep breathes
• Mobilise

If not, then hyperinflation treatment

Question 23

What are the 2 ways of performing hyperinflation treatment?

Answer 23

• Manual

- Ventilator

Question 24

What is manual hyperinflation (MHI)?

Answer 24

• Delivery of slow, deep inspiration greater than baseline tidal volume up to a PIP of 40cm H2O
• Followed by inspiratory hold up to 3s
• Followed by quick, unobstructed expiration

Question 25

What does MHI involve?

Answer 25

- Deep breathing | - Physically disconnecting patient from ventilator & control breathing through resuscitator bag

Question 26

How does MHI work?

Answer 26

- Slow deep inspiration re-expands areas of atelectasis - Inspiratory hold recruits lung segments via collateral changes (improved gas exchange & mobilises secretions - Quick release increases expiratory flow rates, mimics cough, mobilises secretions from distal to proximal segments

Question 27

What are the indications for MHI?

Answer 27

- Evidence of retained secretions - Evidence of collapse/loss of volume - Poor lung compliance (stretch produces surfactant) - Decreased oxygenation cause by one of the above

Question 28

What are the CIs for MHI?

Answer 28

- Undrained pneumothorax - ICC with continuous leak - Bronchopulmonary fistula - Recent oesophageal/lung surgery - Acute respiratory distress syndrome (ARDS)

Question 29

What are the precautions for MHI?

Answer 29

- Unstable CV system - Bronchospasm - PEEP > 15cm H2O - PEEP dependent or high risk of de-recruitment if disconnected from ventilator - Pressure support + PEEP >30cm H2O - FiO2 >60% - PIP >35cm H2O - Raised ICP - Florid APO - Restrictive/obstructive lung disease - Significant pulmonary hypertension - Right ventricular dysfunction

Question 30

What are the practical tips for safe MHI?

Answer 30

- Ensure bag has a filter attached - Attached PEEP valve is patient on PEEP >10cm H2O on ventilator - Ensure max flow from wall prior to disconnecting patient from ventilator - Slow inspiration, as quick a release as possible - Avoid sustained holds if increased intrathoracic pressure - Beware of blowing off too much CO2 (check for spontaneous breaths)

Question 31

How can MHI be used to blow off CO2 & reduce ICP?

Answer 31

- CO2 = acid (vasodilator) - Increase rate or volume to blow off CO2 & reduce ICP - But watch for rebound

Question 32

When is MHI not possible?

Answer 32

- When there is a CI - When risks of disconnecting from ventilator don't outweigh benefit of treatment (Even transient loss of PEEP can worsen atelectasis in some patients) Then consider ventilator hyperinflation

Question 33

What are the benefits of ventilator hyperinflation (VHI)?

Answer 33

- No disconnection from ventilator (no loss of PEEP, no risk of decruitment) - Physio provides deep breaths (with a hold) by manipulating ventilator settings

Question 34

What are the risks of prolonged mechanical ventilation?

Answer 34

- Ventilator associated pneumonia (VAP) | - Respiratory muscle weakness (esp > 7 days)

Question 35

What are the risks of failed extubation & reintubation?

Answer 35

Increased mortality, duration of ventilation & length of stay (more money)

Question 36

What role do physios have in assessing readiness to extubate?

Answer 36

- Know patients on a daily basis - Spend more time with patients - Consider global picture (reconditioning, alertness, cooperation/motivation)

Question 37

What does the assessment for extubation include?

Answer 37

- Overall mental capacity (alert, cooperating) - Coached ventilatory capacity (reliably take a deep breath on command) - Ability to clear secretions independently - Secretion load (can it be managed without suction)

Question 38

What do the results of extubation assessment indicate?

Answer 38

- 4/4: Ready to extubate - 3/4: Some risks, but likely to succeed - 2/4: Borderline, consider carefully (may need extra physio) - 1/4: High risk of failure

Question 39

What are the limitations of extubation?

Answer 39

- Neurological patients: May not be alert but may protect airway sufficiently - Palliation: One-way extubations - Self-extubations (pulling tube out)

Question 40

What did Hodgson et al 2007 find when comparing Laerdal circuit & Mapelson C circuit?

Answer 40

MC circuit cleared 0.89 more per treatment, but no effect on oxygen or compliance