Mechvent Management

A ventilator pressure-volume loop shows no identifiable inflection point on the lower portion. What does this imply?

• Air trapping

• Overdistention

• Poor lung compliance

• Optimal PEEP not reached

Answer explanation

Rationale: Absence of a lower inflection point suggests alveolar collapse – PEEP may need to be increased to keep alveoli open.

A patient is intubated after cardiac arrest. ABG: pH 7.58, PaCO₂ 25 mmHg, HCO₃ 22. What should you do?

• Increase RR

• Decrease RR

• Increase VT

• Increase FiO₂

Answer explanation

Rationale: Respiratory alkalosis → decrease ventilation by reducing RR.

A patient on volume-controlled ventilation suddenly develops a high-pressure alarm. You auscultate wheezing and observe increased PIP with unchanged plateau pressure. What’s the likely cause?

• Circuit leak

• Bronchospasm

• Pneumothorax

• Decreased lung compliance

Answer explanation

Rationale: Wheezing and elevated PIP with stable plateau pressure = increased airway resistance → bronchospasm.

What setting change will directly increase minute ventilation?

• Increasing FiO₂

• Increasing PEEP

• Increasing respiratory rate

• Increasing inspiratory time

Answer explanation

Rationale: Minute ventilation = RR × VT. Increasing RR increases minute ventilation directly.

A patient has sudden desaturation, high PIP, and absent breath sounds on the right. Suspected cause?

• Left lung atelectasis

• Mucus plug in left bronchus

• Tension pneumothorax left side

• Tube migration into right mainstem

Answer explanation

Rationale: ETT in right mainstem bronchus leads to left lung collapse → desaturation + unequal breath sounds.

On the pressure-volume loop, overdistention is observed at the top of the loop. What should be done?

• Add PEEP

• Increase VT

• Increase inspiratory time

• Reduce VT or inspiratory pressure

Answer explanation

Rationale: Overdistention (bird beak pattern) means excessive volume/pressure—reduce to avoid lung injury.

A patient develops hypotension after starting high PEEP. What is the likely cause?

• Hypovolemia

• Reduced venous return

• Increased cardiac output

• Decreased intrathoracic pressure

Answer explanation

Rationale: High PEEP raises intrathoracic pressure, reducing venous return and cardiac output → hypotension.

You notice the flow-time waveform does not return to baseline before the next breath. What does this indicate?

• Auto-PEEP

• Normal flow

• Inspiratory hold

• Excessive tidal volume

Answer explanation

Rationale: Incomplete flow return before exhalation = air trapping = auto-PEEP.

A patient on pressure-controlled ventilation has reduced tidal volume over the past hour. Lung compliance has decreased. What ventilator adjustment is most appropriate?

• Increase FiO₂

• Decrease PEEP

• Increase respiratory rate

• Increase inspiratory pressure

Answer explanation

Rationale: In pressure-controlled ventilation, decreased compliance reduces volume delivery—raising inspiratory pressure restores adequate tidal volume.

A patient receiving mechanical ventilation has the following ABG values:

pH 7.54

• PaCO₂ 26 mmHg

• HCO₃ 24 mEq/L

• PaO₂ 102 mmHg

All of the following ventilator changes may help correct the problem except:

• Switch to SIMV mode

• Increase the respiratory rate

• Add mechanical dead space

• Decrease the tidal volume (VT)

Answer explanation

Rationale:

• -Increasing the respiratory rate would worsen the alkalosis by causing more CO₂ loss.

• -Decreasing tidal volume would lower minute ventilation, retaining more CO₂ → helps correct alkalosis.

• -Switching to SIMV (Spontaneous Intermittent Mandatory Ventilation) allows some spontaneous breathing and can reduce hyperventilation → helps correct alkalosis.

• -Adding mechanical dead space (such as extra tubing) promotes CO₂ retention → helps correct alkalosis.

Thus, the only incorrect action (the one that would make the problem worse) is increasing the respiratory rate.