Assessment of V/Q

Question 1

Normal V/Q averages to _______.

Answer 1

0.8

Question 2

Upper lobes have more _________.

Answer 2

ventilation, with a V/Q of roughly 2.5

Question 3

Lower lobes have more __________.

Answer 3

perfusion, with a V/Q of roughly 0.6

Question 4

There are local regulators of V/Q mismatch: ______________.

Answer 4

high V/Q induces bronchoconstriction due to low alveolar P(CO2)–which lowers the V/Q ratio–and low V/Q induces pulmonary vasoconstriction through low P(a[O2])–which raises the V/Q ratio

Question 5

High V/Q does not ____________.

Answer 5

cause hypoxemia or low P(a[CO2]) until extreme disease states

Question 6

High V/Q is relieved with __________.

Answer 6

exercise

Question 7

Minute ventilation increases in response to ___________.

Answer 7

increased P(a[CO2]) or increased dead space

Question 8

V(A)–the ventilation rate–is equal to ________.

Answer 8

RR x (V[t] - V[D])

Question 9

Alveolar ventilation does not depend on _______.

Answer 9

minute ventilation

Question 10

Alveolar ventilation is increased with _________.

Answer 10

increased tidal volume

Question 11

List five causes of increased dead space.

Answer 11

(1) pulmonary embolism
(2) rapid shallow breathing
(3) decreased cardiac output
(4) mechanical ventilation
(5) emphysema

Question 12

Low V/Q can be distinguished from shunts by ____________.

Answer 12

administering 100% oxygen; low V/Q will correct, while shunts won’t

Question 13

The most common method of detecting shunts is ________.

Answer 13

calculation of the A-a gradient; it is normally supposed to be less than 10

Question 14

Hypoxemia is __________, while desaturation is __________.

Answer 14

low P(a[O2]); low Sp(O2)

Question 15

Pulse oximetry calculates ___________.

Answer 15

oxy-hemoglobin / (oxy- + deoxy-hemoglobin)

Question 16

Met-hemoglobin can be caused by __________.

Answer 16

benzocaine, lidocaine, dapsone, and primaquin

Question 17

Remember, _________ is the treatment for met-hemoglobinemia.

Answer 17

methylene blue

Question 18

What are two causes of hypoxemia with a normal A-a gradient?

Answer 18

Being at altitude and hypoventilation

Question 19

What are three causes of hypoxemia with an increased A-a gradient?

Answer 19

Diffusion limitations (from extreme exercise or interstitial lung disease), shunts, and low V/Q

Question 20

Dead space can lead to high P(a[CO2[). How?

Answer 20

P(a[CO2]) is given by the alveolar ventilation equation: P(a[CO2]) = k x (V[CO2] / V[A]). V(A), in turn, is equal to the following relationship: V(A) = RR x (V[T] - V[dead space]). Thus, increasing dead space decreases respiratory rate.

Question 21

With shunts, _______ and _______ decrease.

Answer 21

P(O2); P(CO2)

Question 22

What are some causes of shunts?

Answer 22

Fluid in the lungs (such as pneumonia exudate or heart failure transudate), regional resistance (airway narrowing, hypoventilation, or diffusion defects), and anatomical causes including tumors

Question 23

Normal A-a gradient is ________

Answer 23

.

Question 24

Percent dead space = __________.

Answer 24

(P[aCO2] - P[eCO2]) / P[aCO2]

Question 25

A shunt does not usually lead to increased _________.

Answer 25

P(a[CO2])

Question 26

If a patient is breathing 100% oxygen, then their shunt will be _____ percent of _______.

Answer 26

1; cardiac output per every 20 Torr difference in the A-a gradient