EDAIC MCQ (Multiple Choice Question) and answer. FREE UPLOADS BY WWW.TARGETEDAIC.COM (79)

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Question: Identify appropriate statements regarding the mechanics of positive pressure ventilation:
a Extrinsic positive end-expiratory pressure (PEEP) less than intrinsic PEEP reduces the elastic work of the respiratory
system.
b. Applying PEEP can reduce oxygen delivery (DO2).
c. A decelerating flow pattern is seen in volume-controlled ventilation.
d. The difference between peak and plateau pressures is greater with volume-controlled ventilation than with pressure-controlled ventilation.
e. Inspiratory hold is required to measure the plateau pressure in pressure-controlled ventilation.

Answers:

1. 1. True
   2. True
   3. False
   4. True
   5. False

Explanation:

Total PEEP is a sum of Intrinsic PEEP and extrinsic PEEP (PEEPi + PEEPe)

PEEP is an increase in the end-expiratory pressure. Ideally, at end-expiration alveolar pressure should equal atmospheric pressure and PEEP should be zero but this is not true always.

Intrinsic PEEPi occurs when the expiratory time is shorter than the time needed to fully deflate the lungs, preventing the lung and chest wall from reaching an elastic equilibrium point. This is sometimes referred to as ‘gas trapping’. During spontaneous ventilation, work must be done to overcome PEEPi before airflow can occur.

Extrinsic PEEPe is positive pressure applied to the expiratory limb of the circuit to maintain positive pressure at the end of expiration, aimed to increase oxygenation.

Applying PEEPe less than the PEEPi will reduce this elastic work required to initiate airflow.

Advantages of PEEP:

• Maintains recruitment of alveoli
• Increases functional residual capacity and
• Minimises intra-pulmonary shunt, thus improving oxygenation.

Disadvantages of PEEP:

• Reduces venous return and therefore cardiac output; oxygen delivery may therefore fall despite an improvement in oxygenation. PEEP must be titrated to achieve a balance between oxygenation and haemodynamic optimisation.
• Increased PVR
• Increased dead space
• decreased hepatic artery and portal venous flow
• increased intracranial pressure (ICP) (due to increased intrathoracic pressure)

Volume-controlled ventilation (VCV) delivers a constant flow and pressure increases linearly until a peak pressure is achieved. When inspiratory pause is added, the pressure falls to reach a plateau pressure (Pplat)

Pressure-controlled ventilation (PCV) produces a decelerating flow pattern and constant pressure is delivered.  In PCV this resistance dissipates during inspiration so that Ppk and Pplat are equal, and thus the difference between the two is minimal.

As the pressure is constantly maintained and equals the plateau pressure, the inspiratory hold is not required to measure the plateau pressure in PCV.

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‘EDAIC MCQ (Multiple Choice Question) and answer’ covers a different topic each day with the intent that candidates can prepare one small topic each day, making steady progress in their exam preparation.