basics

Question 1

alveolar ventilation

Answer 1

the volume of air that enters and exits the alveoli per minute

Question 2

relationship between PaCO2 and alveolar ventilation

Answer 2

PaCO2 ~ (volume produced by body)/alveolar ventilation

therefore, to maintain a constant partial pressure of CO2 in the blood, if the amount of CO2 produced by the body increases, alveolar ventilation must also increase

an increase in the alveolar ventilation, which is a rate, will mean moving greater volume of air into and out of the lungs per minute

Question 3

hypercapnic PaCO2

hypocapnia PaCO2

Answer 3

> 42mmHg

Question 4

how do you calculate PACO2 (partial pressure of oxygen in the alveolus)?

Answer 4

PACO2 = FIO2 x [Pb-Ph2o] - PaCO2/R

= (fraction of oxygen in inspired gas…. usually = 0.21) x (barometric pressure 760-water vapour pressure when gas is fully saturated 47) - (partial pressure of CO2 in the artery)/0.8

(R=0.8… ratio of 2 produced to CO2 consumed)

Question 5

why do we care about the A-a gradient

Answer 5

because it provides a measure for the efficiency of oxygen moving from the alveolus into the blood (measure of the efficiency of gas exchange)

it can help clinicians determine the cause of hypoxemia

Question 6

what is hypoxemia

Answer 6

low partial pressure of oxygen in the blood

Question 7

what is a range of normal A-a difference values?

Answer 7

can range between 5-15mmmHg in A-a gradient, and tends to increase with age