Mechanical Ventilation in ARDS article Flashcards
Low tidal volume ventilation (LTVV) is also referred to as what? And what is the rationale behind it?
- lung protective ventilation
- smaller tidal volumes are less likely to generate alveolar overdistension, one of the principal causes of ventilator-associated lung injury
Define auto-PEEP in relation to low tidal volume ventilation (LTVV).
- in theory, the higher respiratory rates that are used to maintain minute ventilation during LTVV may create auto-PEEP by decreasing the time available for complete expiration
Can breath stacking increase the benefits of LTVV?
- no, breath stacking undermines the benefits of LTVV.
How is the plateau airway pressure measured?
- by using a 0.5 second inspiratory breath hold
- this is checked at least every 4 hours and after each change in PEEP or tidal volume
- the goal plateau pressure is < 30 cm H2O
What is a reasonable oxygenation goal during LTVV? (PaO2 and SpO2)
PaO2: 55 - 80 mmHg
SpO2: 88 - 95 %
(these numbers are achieved by adjusting the FiO2 and the PEEP)
Is permissive hypercapnia okay when you’re using LTVV?
- yes
(LTVV frequently requires permissive hypercapnic ventilation (PHV), a ventilatory strategy that accepts alveolar hypoventilation in order to maintain a
low alveolar pressure and minimize the complications of alveolar overdistension (eg,
ventilator-associated lung injury). Hypercapnia and respiratory acidosis are a consequence of this strategy)
How can the degree of hypercapnia be minimized during LTVV?
2 ways
- by using the highest respiratory rate that does not induce auto-PEEP
- shortening the ventilator tubing to decrease dead space
Open lung ventilation is a strategy that combines what two things?
- low tidal volume ventilation (LTVV)
- enough applied PEEP to maximize alveolar recruitment
(The LTVV aims to mitigate alveolar overdistension, while the applied PEEP seeks to minimize cyclic atelectasis. Together, these effects are expected to decrease the risk of ventilator-associated lung injury)
The high PEEP approach is a type of open lung ventilation that does not require what?
- pressure-volume curves
(This is advantageous because pressure-volume curves are difficult to construct and generally require neuromuscular blockade)
What is the rationale for delivery of a high level of applied PEEP?
- the applied PEEP opens collapsed alveoli, which decreases alveolar overdistension because the volume of each subsequent tidal breath is shared by more open alveoli.
- If the alveoli remain open throughout the respiratory cycle, cyclic atelectasis is also reduced.
Define recruitment maneuver.
- A recruitment maneuver is the brief application of a high level of continuous positive airway pressure, such as 35 to 40 cm H2O for 40 seconds.
What is the purpose of recruitment maneuvers?
- to open alveoli that have collapsed
Can ARDS patients be supported with a volume limited mode, a pressure limited mode, or both?
- both
(In most patients with ARDS, a volume limited mode will produce a stable airway pressure and a pressure limited mode will deliver stable tidal volumes, assuming that breath to breath lung mechanics and patient effort are stable)
If refractory hypoxemia occurs even with optimized PEEP and FiO2, what can you do to improve oxygenation?
- increasing the I:E ratio by prolonging inspiratory time may improve oxygenation
(Prolonging the inspiratory time can be an effective means of improving oxygenation in
some patients with ARDS because the parenchymal abnormalities are heterogeneous, with different areas of the lung requiring more time to open and participate in gas exchange)
When you prolong the inspiratory time, what deleterious effects may occur? (5 things)
- air trapping
- auto-PEEP
- barotrauma
- hemodynamic instability
- decreased oxygen delivery
