Mechanical Ventilation & Hyperinflation Flashcards
What are the 2 reasons why patients need mechanical ventilation?
Respiratory failure
- Type 1 or 2
Airway protection
- Intubation due to airway compromise (e.g. stridor)
- Drug-induced coma
Why do patients with respiratory failure require mechanical ventilation?
- Pump stops working
- diaphragm, rib cage, nerves, muscles
- due to injury/pain or neural defect (e.g. brainstem infarct) - Gas exchange surface compromised
- needs high level of pressure to guarantee adequate O2 into bloodstream
- e.g. pneumonia, inflammation
What are the causes of respiratory failure?
- Opioid drug use
- Cervical spinal cord injury
- Surgery/general anaesthetic
- Rib fractures
- APO
- PE
- Post-op atelectasis
- Pneumonia
What is the function of a ventilator?
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
What is positive end expiratory pressure (PEEP)?
Baseline pressure maintained in the lungs at the end of each exhalation
Why is PEEP important?
- 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
What is pressure support?
If a patient can start a tiny breath, a ventilator will recognise it & boost it to make it a decent size breath
What is the difference between pressure support & controlled ventilation?
- Support: Patient is in charge of starting the breath
- Controlled: Ventilator is in charge of starting the breath
How does pressure support mode work?
- Baseline PEEP
- Recognises start of a breath
- Boosts each spontaneous breath to pre-set pressure
What are the benefits of pressure support?
- Comfortable for patient
- Reduces WOB
What are the two delivery modes of controlled mandatory ventilation (CMV)?
- 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
Why is CMV not commonly used?
- Patients require sedation/paralysis
- If patient wakes up it’s not comfortable or appropriate
What is synchronised intermittent mandatory ventilation (SIMV)?
- 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
What are the benefits of SIMV?
- 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
What are the other less commonly used modes of ventilation?
- Pressure control inverse ratio ventilation
- Airway pressure release ventilation (APRV)
- BiLevel ventilation
- High frequency/oscillation ventilation
What is the meaning of the following terms:
- PIP
- ETCO2
- Vt
- Tinsp
- MV
- PIP: Peak inspiratory pressure (PEEP + PS)
- ETCO2: End-tidal CO2
- Vt: Tidal volume
- Tinsp: Inspiratory time (s)
- MV: Minute ventilation (RR x Vt)
What role do physios have in ventilation?
- 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
What are the complications of mechanical ventilation?
- 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
Why is impaired V/Q matching a complication of mechanical ventilation?
- 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
What do the mechanical ventilation complications often lead to?
- Atelectasis/collapse
- Difficulty clearing sputum
What are invasively ventilated patients unable to do?
- Truly cough/huff (ETT/trache prevents closure of glottis)
- Expectorate sputum easily (dependent on suction)
- Participate in PEP therapy
What are some of the things that patients who are awake and invasively ventilated may be able to do?
- Take deep breathes
- Mobilise
If not, then hyperinflation treatment
What are the 2 ways of performing hyperinflation treatment?
- Manual
- Ventilator
What is manual hyperinflation (MHI)?
- 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
What does MHI involve?
- Deep breathing
- Physically disconnecting patient from ventilator & control breathing through resuscitator bag
How does MHI work?
- 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
What are the indications for MHI?
- Evidence of retained secretions
- Evidence of collapse/loss of volume
- Poor lung compliance (stretch produces surfactant)
- Decreased oxygenation cause by one of the above
What are the CIs for MHI?
- Undrained pneumothorax
- ICC with continuous leak
- Bronchopulmonary fistula
- Recent oesophageal/lung surgery
- Acute respiratory distress syndrome (ARDS)
What are the precautions for MHI?
- 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
What are the practical tips for safe MHI?
- 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)
How can MHI be used to blow off CO2 & reduce ICP?
- CO2 = acid (vasodilator)
- Increase rate or volume to blow off CO2 & reduce ICP
- But watch for rebound
When is MHI not possible?
- 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
What are the benefits of ventilator hyperinflation (VHI)?
- No disconnection from ventilator (no loss of PEEP, no risk of decruitment)
- Physio provides deep breaths (with a hold) by manipulating ventilator settings
What are the risks of prolonged mechanical ventilation?
- Ventilator associated pneumonia (VAP)
- Respiratory muscle weakness (esp > 7 days)
What are the risks of failed extubation & reintubation?
Increased mortality, duration of ventilation & length of stay (more money)
What role do physios have in assessing readiness to extubate?
- Know patients on a daily basis
- Spend more time with patients
- Consider global picture (reconditioning, alertness, cooperation/motivation)
What does the assessment for extubation include?
- 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)
What do the results of extubation assessment indicate?
- 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
What are the limitations of extubation?
- Neurological patients: May not be alert but may protect airway sufficiently
- Palliation: One-way extubations
- Self-extubations (pulling tube out)
What did Hodgson et al 2007 find when comparing Laerdal circuit & Mapelson C circuit?
MC circuit cleared 0.89 more per treatment, but no effect on oxygen or compliance
