Resp failure

Question 1

definition of resp failure

Answer 1

resp system fails to achieve an arterial pressure of O2 that is sufficient to meet the needs of the body

Question 2

categories of resp failure

Answer 2

type I: Low O2 with normal or low CO2. usually a problem with the lungs themselves
type II: Low O2 with high CO2. usually a problem with ventilation of the lung (ie. central resp drive defect, paralysis of diaphragm).
There are also non-pulmonary causes of ischemia, but these aren’t considered resp failure

Question 3

when does PaO2 become clinically significant. why.

Answer 3

usually below 60 mmHg. below this point on the hemoglobin saturation curve, we see linear precipitous drop in Hb-O2 binding

Question 4

Equation for PAO2 at sea level

Answer 4

PAO2 = 150 - (1.25 *PCO2) at sea level

Question 5

4 main mechanisms of hypoxemia in type I resp failure

Answer 5

1. Inadequate O2 supply
2. V/Q mismatch (ventilation perfusion mismatch)
3. Right to left shunt
4. Diffusion abnormalities

Question 6

Resp failure and inadequate O2 supply. Include equation. change in PaO2-PAO2 gradient?

Answer 6

may be inadequate inspiratory O2 supply. PAO2 = FIO2 (Pb-PH2O). fraction of inhaled oxygen is rarely changed but barometric pressure may be reduced (high altitudes).
Inadequate inspiratory O2 does NOT cause a change in PaO2-PAO2 gradient.

Question 7

Ventilation/perfusion mismatch. What happens. What does body do. change in PaO2-PAO2 gradient?

Answer 7

maldistribution of ventilation and perfusion within regions of the lung. Low alveolar O2 concentrations in areas that aren’t sufficiently ventilated. this blood then mixes with well ventilated, well perfused areas, and they can’t compensate, so overall O2 is lower than it needs to be. Note that body sometimes compensates by constricting blood supply to non-ventilated areas.
change in PaO2 and PAO2 gradient seen.

Question 8

V/Q mismatch treatment

Answer 8

treat with supplemental O2. this will allow more O2 into the poorly ventilated areas. this O2 will get into the blood, bc these patients DON’T have a problem with diffusion.

Question 9

Right to left shunt. change in PaO2-PAO2 gradient.

Answer 9

blood enters the arteries without passing though the lungs. some examples are normal (bronchial arteries, pulmonary veins, coronary veins bringing blood into L ventricle), but many are pathological (patent formaen ovale + HTN; VSD, arteriovenous malformations). may decrease PaO2-PAO2 gradient
Does NOT respond to supplemental O2.

Question 10

DIffusion abnormalities. Important factors

Answer 10

Alveoli is perfused and ventilated, but gas exchange is dysfunctional.
decreased surface area, increased thickness, decreased pressure gradient.
Supplemental O2 helps.

Question 11

Type II resp failure types

Answer 11

imbalance btw resp. pump and the load on the resp pump. Increased CO2.
May be pump problems: hypoventilation
or Load problems: increased resistance, or decreased compliance

Question 12

Hypoventilation. causes. change in PaO2-PAO2 gradient.

Answer 12

can’t deliver O2 b/c patient isn’t breathing enough. may be a NMJ disease, narcotics, brainstem prob, hypothyroidism, side effect of some corticosteroids which cause muscle atrophy.
A-a gradient is unchanged.

Question 13

What are resistive and compliance loads?

Answer 13

resistive: resistence is very high, so flow into lungs is decreased. think of bronchospasm, secretions, edema, etc
Or, compliance load: if lungs less compliant, hard to move air in and out because lungs won’t get bigger/smaller. think pneumonia, pleural effusion, pneumothorax.