36. Respiratory Failure

Question 1

Define respiratory failure

Answer 1

failure of the resp system to do its job: delivery of adequate 02 to arterial blood, removal of C02 from mixed venous blood

Question 2

what is the onset of resp failure?

Answer 2

can be acute, sub-acute or chronic

Question 3

what causes resp failure?

Answer 3

a wide variety of diseases

Question 4

Two types of resp failure?

Answer 4

hypoxemic v hypercapnic (ventilatory)

Question 5

what are the general mechanisms that cause hypoxemic resp failure?

Answer 5

shunt, VQ mismatch, hypoventilation, diffusion impairment, decr FI02.
usually shunt or low VQ!

Question 6

with VQ mismatch, what happens to the Aa difference?

Answer 6

widens

Question 7

with hypoventilation, what happens to the Aa difference?

Answer 7

normal

Question 8

with a shunt, what happens to the Aa difference?

Answer 8

widens

Question 9

with diffusion impairment, what happens to the Aa difference?

Answer 9

widens

Question 10

what is the most common clinical syndrome associated with hypoxemic resp failure?

Answer 10

ARDS

Question 11

what are VA, VE, and VD?

Answer 11

VA = alveolar ventilation
VE = overall ventilation
VD = dead space ventilation

Question 12

what is the formula involving VA, VE, VD?

Answer 12

VA = VE-VD

Question 13

when will VA be low?

Answer 13

when VE is decreased (hypoventilation) or when VD is high (high amt of dead space)

Question 14

why does hypercapnic resp failure occur?

Answer 14

failure of resp muscles to provide adequate alveolar ventilation. usually due to CNS depression (low VE), resp muscle weakness (low VE) or imbalance between ventilatory supply and demand

Question 15

how do we treat hypoxemia?

Answer 15

• hypoventilation and diffusion impairment –> supplemental 02
• VQ mismatch –> supp 02 possibly
• hyperventilation if problem is due to hypoventilation
• PEEP

Question 16

which is worse: hypoxemia or hypercapnia?

Answer 16

hypoxemia. we can tolerate a lot of hypercapnia and acidosis.

Question 17

what is the difference between positive pressure and negative pressure ventilation?

Answer 17

pos pressure: raise pressure at the mouth or airway. neg pressure vents lower pressure at the alveoli. either way a pressure gradient develops which drives inspiration

Question 18

what is the difference between volume targeted and pressure targeted ventilation?

Answer 18

volume targeted: set a tidal volume and generate whatever pressure is needed to deliver that volume.
pressure targeted: set a fixed pressure, and the volume delivered depends on a lot of factors incl patient characteristics.

Question 19

what is PEEP? what does it do?

Answer 19

positive end-expiratory pressure. maintains expiratory pressure at a level sufficient to keep alveolus from collapsing so that during the next breath, a greater volume change can occur

Question 20

adverse consequences of PEEP?

Answer 20

increased thoracic pressure decr venous return.