Ventilation

Question 1

What PaO₂ level indicates need for mechanical ventilation?

Answer 1

PaO₂ < 6.67 kPa (50 mmHg) on room air.

Question 2

What PaCO₂ level indicates ventilatory failure?

Answer 2

PaCO₂ > 6.67 kPa (50 mmHg) on room air in the absence of metabolic acidosis.

Question 3

What does an elevated PaCO₂ indicate clinically?

Answer 3

Ventilatory failure (hypoventilation).

Question 4

What is the PF ratio?

Answer 4

PaO₂ / FiO₂
(PaO₂ in mmHg, FiO₂ as a decimal).

Question 5

What PF ratio suggests need for mechanical ventilation?

Answer 5

PF ratio < 300.

Question 6

How is FiO₂ expressed in the PF ratio?

Answer 6

As a decimal (e.g. 40% = 0.4).

Question 7

What conversion factor is important for PaO₂ units?

Answer 7

1 kPa = 7.5 mmHg.

Question 8

What tidal volume suggests respiratory muscle failure?

Answer 8

Tidal volume < 5 mL/kg
(e.g. <350 mL in a 70-kg patient).

Question 9

What vital capacity suggests impending respiratory failure?

Answer 9

Vital capacity < 15 mL/kg
(e.g. <1050 mL in a 70-kg patient).

Question 10

Why are tidal volume and vital capacity important?

Answer 10

They assess respiratory muscle strength and reserve

Question 11

What respiratory rate suggests need for mechanical ventilation?

Answer 11

RR > 35 breaths/min (especially if sustained).

Question 12

What clinical signs suggest respiratory distress?

Answer 12

Nasal flaring

Use of accessory muscles

Increased work of breathing

Fatigue or altered mental status

Question 13

Why are clinical signs important even if ABGs are borderline?

Answer 13

Because clinical deterioration precedes ABG collapse

Question 14

Single most important principle when deciding to ventilate?

Answer 14

Treat the patient, not just the ABG.

Question 15

When should mechanical ventilation NOT be delayed?

Answer 15

When there is worsening respiratory distress, fatigue, or altered consciousness, even before ABGs worsen.