Vent, Resp Failure - Muthiah

Question 1

what specifically do the central chemoreceptors respond to and what is the effect?

Answer 1

they respond to increased [H+], or dec pH, in the CSF as a result of inc pCO2 - the result is in an increase in ventilation to exhale more CO2

Question 2

What is Muthiah definition of ventilatory failure

Answer 2

any time CO2 is retained (hypercapnia)

Question 3

respiratory failure can be of what two types

Answer 3

type I - pure hypoxemia

type II - hypoxemia + hypercapnia (this is ventilatory failure)

Question 4

What are 3 mechanisms of hypoxemic failure

Answer 4

1 - V/Q mismatch
2 - shunt
3 - exacerbated by low mixed venous O2

Question 5

what are 2 mechanisms of hypercapnic failure

Answer 5

1 - decreased minute ventilation (MV) relative to demand

2 - increased dead space ventilation

Question 6

recall the 3 mechanisms of hypoxic resp failure that cause a wide A-a

Answer 6

1 - V/Q mismatch
2 - R - to - L Shunt
3 - diffusion limitation

Question 7

recall the 2 mechanisms of hypoxic resp failure that causes normal A-a

Answer 7

1 - hypoventilation

2 - decreased PiO2

Question 8

what is the essential pathophys behind hypercapnia with regards to the alveoli

Answer 8

in order to have retained CO2, there must be a decrease in alveolar ventilation at some level

Question 9

what are 4 general causes of hypercapnic resp failure

Answer 9

1 - central hypoventilation
2 - neuropathies
3 - muscle (pump) failure
4 - airway obstruction

Question 10

what are 3 causes of a right shift in the hemoglobin binding curve (i.e. decreased affinity for O2)

Answer 10

1 - inc Temp
2 - acidosis (indication of inc CO2)
3 - inc 2,3 DPG

mnemonic TAP

Question 11

What 4 factors will cause a left shift of the hemoglobin binding curve (i.e. increased affinity for O2)

Answer 11

1 - dec Temp
2 - alkalosis
3 - dec 2,3 DPG or fetal hemoglobin (does not bind 2,3 DPG as well)
4 - CO (carbon monoxide)

Question 12

Formoterol is a long acting Beta 2 agonist with a rapid onset of action. Can it be used for rescue?

Answer 12

no

Question 13

What management strategy of respiratory failure should you not overlook and what is the methodology behind it

Answer 13

hydration - pt is losing water as moisture in their breath, and these pts are hyperventilating, so losing more water than nml

Question 14

What treatment strategy, as an alternative to intubation, can be applied to a pt with respiratory failure from and asthma or COPD exacerbation that is worsening?

Answer 14

BiPap - noninvasive way to provide pressure support and PEEP

Question 15

What is the Haldane effect?

Answer 15

Haldane effect: deoxygenated blood has a better capacity to carry CO2; oxygenated blood has a reduced capacity to carry CO2
In hypoxic individuals, some CO2 is bound to hemoglobin as carbaminohemoglobin. Supplemental O2 100%, will raise the PaO2 and the SaO2. CO2 must be displaced from Hb, and this readily happens in the presence of inc pO2 (This is the Haldane effect - inc O2 causes displacement of CO2 so O2 can bind, and vice versa) this displaced CO2 then can only dissolve in the blood and this raises the PCO2

Question 16

what are two indications that a pt is hypoxic? one physical exam finding, one lab finding

Answer 16

tachypnea and an O2 sat less than 90

Question 17

what is a good indication of hypercapnia (looking at blood)?

Answer 17

a bicarb higher than 30 on the serum analysis

Question 18

what is the evaluation of choice in pts suspected of PE?

Answer 18

helical CT

Question 19

when should you not do PFTs?

Answer 19

acute situations - ARDS, pneumonia, PE, other acute shit

Question 20

How do you treat the pt in hypoxic respiratory failure?

Answer 20

supplemental O2

Question 21

What is the most common mechanism of hypoxemia?

Answer 21

V/Q mismatch

Question 22

Again, how do we differentiate between V/Q mismatch and Shunt as mechanism for hypoxia?

Answer 22

give supplemental oxygen
if it corrects - V/Q mismatch
if not - shunt

Question 23

in what patients do anticholinergics work best in?

Answer 23

COPD - often times can have an inc vagal tone

Question 24

How do you know if the pt is getting tired (i.e. losing muscular ability to breathe?)

Answer 24

increased somnolence, decreased RR, etc.

Question 25

what is significant of an acute pt that is getting tired - what is the mechanism of this exacerbation? (I can’t think how to ask this)

Answer 25

CO2 acts as a narcotic - why fatigue and CO2 retention is a vicious cycle - as pt gets tired, they breathe less, and expel less CO2, which causes more fatigue and less breathing

Question 26

what will ABG show in pt that is getting tired

Answer 26

CO2 retention

Question 27

Should pts w/ COPD be given O2, since it causes the pt to retain CO2? and why? (What are the 2 reasons for inc CO2)

Answer 27

yes they should

the resultant V/Q inequality, along with the Haldane effect are the most significant causes of hypercapnea

Question 28

Supplemental oxygen given to a pt w/ chronic hypercapnia can cause an increase in PCO2. what is the mechanism behind the worsening V/Q mismatch?

Answer 28

worsening V/Q mismatch: supplemental O2 demolishes the hypoxic induced vasoconstriction of the pulmonary vasculature
release of hypoxic vasoconstriction in poorly ventilated areas of the lung is caused by an increase in PaO2
Consequnce: there is increased blood flow to low V/Q areas and a worsening of V/Q inequality which exaggerates the degree of CO2 retention