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Critical care > Mechanical Ventillation > Flashcards

Mechanical Ventillation Flashcards

1
Q

Patient Causes for high airway pressure (volume control modes) / low tidal volume (pressure control modes)

A

Patient

  • bronchospasm
  • reduced lung compliance
    • pulmonary oedema
    • ARDS
    • collapse
  • reduced pleural compliance (e.g., pneumothorax)
  • reduced chest wall compliance (e.g., massive ascites)
  • ventillator dyssynchrony
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2
Q

Equipment Causes for high airway pressure (volume control modes) / low tidal volume (pressure control modes)

A

ETT

  • kinking
  • blocked

Circuit

  • condesation in tubing
  • kinking
  • wet filter

Ventillator

  • inappropriate settings
  • malfunction
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3
Q

Approach to hypotensive patient immediately post intubation (three initial steps)

A
  1. Give fluid
  2. Disconnect from circuit and hand bag
  3. Consider needle thoracostomy
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4
Q

Causes of hypotension immediately post intubation

A
  1. Drugs
  2. Gas trapping
  3. Pneumothorax
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5
Q

Three immediate steps for hypoxic, intubated patient

A
  1. Confirm adequate pulse oximetry waveform
  2. Increase FiO2 to 1.0
  3. Confirm ventillation
  • tube fogging
  • end-tidal CO2
  • chest wall movements
  • auscultate for air entry
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6
Q

Approach to hypoxic, intubated patient with poor ventillation (e.g., chest wall not moving, low tidal volumes/high pressures)

A
  1. Confirm adequate pulse oximetry waveform
  2. Increase FiO2 to 1.0
  3. Confirm ventillation
    • tube fogging
    • end-tidal CO2
    • chest wall movements
    • auscultate for air entry
  4. Disconnect from circuit and manually ventillate
  5. Assess ease of manual ventillation
  • Difficult
    • ETT/patient problem
  • Easy
    • Ventillator problem
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7
Q

Approach to hyoxic intubated patient with adequate ventillation

A
  1. Confirm adequate pulse oximetry waveform
  2. Increase FiO2 to 1.0
  3. Confirm ventillation
    • tube fogging
    • end-tidal CO2
    • chest wall movements
    • auscultate for air entry
  4. Assess patient for:
    • pneumothorax
    • collapse
    • pulmonary oedema
    • bronchospasm
  5. Treat and adjust ventillator
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8
Q

Equation for total airway pressure (inspiratory)

A

Total airway pressure = airway pressure + alveolar pressure

Total airway pressure = flow x resistance + volume/compliance + PEEP

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9
Q

Define inspiratory airway pressure

A

The pressure during inspiration caused by airway resistance to flow and alveolar compliance

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10
Q

What determines mean alveolar pressure?

A
  • Tidal volume OR inspiratory pressure
  • Inspiratory time
  • PEEP
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11
Q

How can mechanical ventillation be adjusted to improve oxygenation?

A
  • Increase FiO2
  • Increased mean alveolar pressure
    • increase inspiratory time
    • increase tidal volume OR inspiratory pressure
    • increase PEEP
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12
Q

List adverse effects of mechanical ventillation

A

Barotrauma

Gas trapping

Oxygen toxicity

Cardiovascular depression

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13
Q

What factors contribute to barotrauma

A

High tidal volume

High maximum alveolar pressure

High shear forces

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14
Q

List five barotrauma related injuries

A
  1. Pneumothorax
  2. Pneumomediastinum
  3. Pneumopericardium
  4. Surgical emphysema
  5. Acute lung injury
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15
Q

Strategies for increasing carbon dioxide elimination

A
  1. increase tidal volume
  2. increase respiratory rate
  3. decrease dead space
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16
Q

What two factors is the arterial pCO2 dependent upon?

A
  1. Alveolar ventillation
  2. CO2 production
17
Q

What determines alveolar ventillation?

A

Alveolar ventillation (minute ventillation) = respiratory rate x (tidal volume - dead space)

18
Q

List three cardiovascular effects of positive pressure ventillation

A
  • Reduced venous return (preload)
  • Reduced afterload
  • Reduced myocardial oxygen consumption
19
Q

What factors reduce venous return (preload) in positive pressure ventillation?

A
  • high inspiratory pressure
  • high PEEP
  • prolonged inspiratory time
20
Q

Describe how afterload is reduced during positive pressure ventillation

A

Afterload = ventricular wall tension

Ventricular wall tension = ( transmural pressure x radius ) / ( 2 x wall thickness)

Transmural pressure = intraventricular pressure - intrapleural pressure

Positive pressure ventillation increases intrapleural pressure, thereby reducing transmural pressure.

21
Q

Define compliance

A

It expresses distensibility; that is, the tendency of a chamber to increase in volume when exposed to a given distending pressure

22
Q

State the equation describing static thoracic compliance

A

Cstat = VT / [Pplateau - PEEP(tot)]

( Compliance = ∆volume / ∆pressure )

23
Q

What are the four targets for the ARDSnet lung protective ventillation strategy?

A
  1. Tidal volume 6mL/kg (predicted body weight)
  2. Plateau pressure ≤ 30mmH2O
  3. pH 7.3 to 7.45 (permissive hypercapnia)
  4. I:E ratio ≤ 1

Source

24
Q

What is the effect of positive pressure ventillation on a volume depleted patient?

A

Reduced cardiac output (impaired filling due to raised intrathoracic pressure)

25
Q

What is the effect of positive pressure on the failing heart?

A

Increased cardiac output (reduced afterload effect dominant, preload likely to be excessive)

26
Q

Define closing pressure

A

The transpulmonary pressure at which distal airspaces begin to collapse

27
Q

Give two examples of disease states increasing closing pressure

A

COPD

ARDS

28
Q

What are the two possible alveolar effects of increasing PEEP?

A
  • Alveolar recruitment
  • Alveolar overdistension

(Dependent on recruitable lung volume)

29
Q

What two observations can indicate PEEP is promoting alveolar recruitment?

A
  • increased lung compliance
  • improved oxygenation (e.g., A-a gradient; PAO2/FiO2 ratio)
30
Q

List contraindications to non-invasive ventillation

A

A — unprotected airway, obstruction, oesophageal/max.facs surgery

B — untreated pneumothorax, (impending) respiratory arrest

C — shock

D — altered mental status (agitation vs. sedation), head trauma/surgery (esp. base of skull fracture — risk of pneumocephalus)

31
Q

List indications for mechanical ventillation (A to E then other)

A

A – protection and patency
B – respiratory failure (hypercapnic or hypoxic)
C – minimise oxygen consumption and optimize oxygen delivery (e.g. sepsis)
D – unresponsive to pain, terminate seizure, prevent secondary brain injury
E — temperature control (e.g. serotonin syndrome)

Other — safety for transport (e.g. psychosis), humanitarian reasons

32
Q

Complications of NIV

A
  • air swallowing with abdominal distension -> vomiting and aspiration
  • hypotension (if hypovolaemic)
  • raised ICP
  • increased intraocular pressure
  • claustrophobia/anxiety
  • agitation
  • pressure ulcers/necrosis (nasal bridge)
  • facial or ocular abrasions
33
Q

What is the rationale for protective lung ventillation in ARDS?

A
  • low tidal volume ventilation reduces ventilator-associated lung injury (VALI)
    • volutrauma (hyperinflation and shearing injury)
    • barotrauma (alveolar rupture and pneumothorax)
    • biotrauma (release of inflammatory mediators)
  • hypercapnia may also have directly beneficial effects in ARDS
  • clear evidence for benefit in ARDS in animals and humans
34
Q

What are the four targets for the ARDSnet lung protective ventillation strategy?

A
  1. Tidal volume 6mL/kg (predicted body weight)
  2. Plateau pressure ≤ 30mmH2O
  3. pH 7.3 to 7.45 (permissive hypercapnia)
  4. I:E ratio ≤ 1

Source

35
Q

What are the three pathophysiological processes in ventillator-associated lung injury (VALI)?

A
  1. volutrauma (hyperinflation and shearing injury)
  2. barotrauma (alveolar rupture and sequelae)
  3. biotrauma (release of inflammatory mediators)

Critical care (10 decks)

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