36. Respiratory Failure Flashcards
Define respiratory failure
failure of the resp system to do its job: delivery of adequate 02 to arterial blood, removal of C02 from mixed venous blood
what is the onset of resp failure?
can be acute, sub-acute or chronic
what causes resp failure?
a wide variety of diseases
Two types of resp failure?
hypoxemic v hypercapnic (ventilatory)
what are the general mechanisms that cause hypoxemic resp failure?
shunt, VQ mismatch, hypoventilation, diffusion impairment, decr FI02.
usually shunt or low VQ!
with VQ mismatch, what happens to the Aa difference?
widens
with hypoventilation, what happens to the Aa difference?
normal
with a shunt, what happens to the Aa difference?
widens
with diffusion impairment, what happens to the Aa difference?
widens
what is the most common clinical syndrome associated with hypoxemic resp failure?
ARDS
what are VA, VE, and VD?
VA = alveolar ventilation VE = overall ventilation VD = dead space ventilation
what is the formula involving VA, VE, VD?
VA = VE-VD
when will VA be low?
when VE is decreased (hypoventilation) or when VD is high (high amt of dead space)
why does hypercapnic resp failure occur?
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
how do we treat hypoxemia?
- hypoventilation and diffusion impairment –> supplemental 02
- VQ mismatch –> supp 02 possibly
- hyperventilation if problem is due to hypoventilation
- PEEP
which is worse: hypoxemia or hypercapnia?
hypoxemia. we can tolerate a lot of hypercapnia and acidosis.
what is the difference between positive pressure and negative pressure ventilation?
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
what is the difference between volume targeted and pressure targeted ventilation?
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.
what is PEEP? what does it do?
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
adverse consequences of PEEP?
increased thoracic pressure decr venous return.
