Assessment of V/Q Flashcards
Normal V/Q averages to _______.
0.8
Upper lobes have more _________.
ventilation, with a V/Q of roughly 2.5
Lower lobes have more __________.
perfusion, with a V/Q of roughly 0.6
There are local regulators of V/Q mismatch: ______________.
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
High V/Q does not ____________.
cause hypoxemia or low P(a[CO2]) until extreme disease states
High V/Q is relieved with __________.
exercise
Minute ventilation increases in response to ___________.
increased P(a[CO2]) or increased dead space
V(A)–the ventilation rate–is equal to ________.
RR x (V[t] - V[D])
Alveolar ventilation does not depend on _______.
minute ventilation
Alveolar ventilation is increased with _________.
increased tidal volume
List five causes of increased dead space.
(1) pulmonary embolism
(2) rapid shallow breathing
(3) decreased cardiac output
(4) mechanical ventilation
(5) emphysema
Low V/Q can be distinguished from shunts by ____________.
administering 100% oxygen; low V/Q will correct, while shunts won’t
The most common method of detecting shunts is ________.
calculation of the A-a gradient; it is normally supposed to be less than 10
Hypoxemia is __________, while desaturation is __________.
low P(a[O2]); low Sp(O2)
Pulse oximetry calculates ___________.
oxy-hemoglobin / (oxy- + deoxy-hemoglobin)
Met-hemoglobin can be caused by __________.
benzocaine, lidocaine, dapsone, and primaquin
Remember, _________ is the treatment for met-hemoglobinemia.
methylene blue
What are two causes of hypoxemia with a normal A-a gradient?
Being at altitude and hypoventilation
What are three causes of hypoxemia with an increased A-a gradient?
Diffusion limitations (from extreme exercise or interstitial lung disease), shunts, and low V/Q
Dead space can lead to high P(a[CO2[). How?
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.
With shunts, _______ and _______ decrease.
P(O2); P(CO2)
What are some causes of shunts?
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
Normal A-a gradient is ________
.
Percent dead space = __________.
(P[aCO2] - P[eCO2]) / P[aCO2]
A shunt does not usually lead to increased _________.
P(a[CO2])
If a patient is breathing 100% oxygen, then their shunt will be _____ percent of _______.
1; cardiac output per every 20 Torr difference in the A-a gradient
