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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
What is the effect of positive pressure on the failing heart?
Increased cardiac output (reduced afterload effect dominant, preload likely to be excessive)
26
Define closing pressure
The transpulmonary pressure at which distal airspaces begin to collapse
27
Give two examples of disease states increasing closing pressure
COPD ARDS
28
What are the two possible alveolar effects of increasing PEEP?
* Alveolar recruitment * Alveolar overdistension (Dependent on recruitable lung volume)
29
What two observations can indicate PEEP is promoting alveolar recruitment?
* increased lung compliance * improved oxygenation (e.g., A-a gradient; PAO2/FiO2 ratio)
30
List contraindications to non-invasive ventillation
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
List indications for mechanical ventillation (A to E then other)
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
Complications of NIV
* 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
What is the rationale for protective lung ventillation in ARDS?
* 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
What are the four targets for the ARDSnet lung protective ventillation strategy?
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 ## Footnote [Source](http://www.ardsnet.org/system/files/6mlcardsmall_2008update_final_JULY2008.pdf)
35
What are the three pathophysiological processes in ventillator-associated lung injury (VALI)?
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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