V/Q Matching

Question 0

V/Q ratio locations

Answer 0

Are relative to gravity; higher at the top of the lungs, lower at the bottom

Question 1

A-a Gradient

Answer 1

PACo2-PaCo2

Should not be >15mmhg

*Determines the presence of low V/Q units

Question 2

Single Lung Transplants

Answer 2

Used to treat fibrosis pts.; ventilation will go to the transplanted lung w/ less recoil

*Bad for emphysema pts=> ventilation still goes to the more compliant lung whereas the perfusion goes to the transplanted lung

Question 3

Treatment for Right Heart Failure

Answer 3

NO inhalation; selective dilation of vessels participating in gas exchange will lower the workload of the right ventricle

• CANNOT BE GREATER than 20ppm
• Ingested NTP would dilate all vessels-even the ones not participating in gas exchange

Question 4

Anatomic Shunts

Answer 4

Shunts that dump unsaturated, venous blood into the systemic circulation

*Such as the bronchial arteries

Question 5

Intrapulmonary Shunts

Answer 5

Blood that travels thru the pulmonary circulation but acts w/ underventilated alveoli

Question 6

3 Findings of Low V/Q Unit

Answer 6

1. Decreased PaO2 (hypoxemia)
2. Increased A-a
3. Increased PCO2 (hypercapnia)

Question 7

Shunt Equation

Answer 7

Qs/Qt= CcO2-CaO2/ CcO2-CvO2

Question 8

Compensation mechanisms for a V/Q mismatch

Answer 8

1 Smooth muscle contraction

2. Hyperventilation
   * Chronic constriction off smooth muscle can lead to pulmonary hypertension and right heart failure

Question 9

Paradox of Compensation

Answer 9

PaCO2 is normal

PaO2 is still low; this is due to most of the air traveling to the pathway w/ less resistance which already had a normal pO2

Question 10

Diagnosing a Shunt

Answer 10

Give the pt. 100% O2 => the pO2 will not substantially rise

Question 11

Diagnosing a low V/Q mismatch

Answer 11

Give the pt. 100% O2 => pO2 will substantially rise

Question 12

Five Causes for Hypoxemia

Answer 12

Normal A-a:
Low PiO2
Hypoventilation

Increased A-a:
Shunt
Low V/Q
Diffusion issues

Question 13

High V/Q Ratios

Answer 13

1. Pulmonary Embolisms- Area in lungs becomes dead space
   * Can cause the release of inflammatory agents that will alter capillary permeability and collapse alveoli => SHUNTS; especially bad here
2. Lung Geometry- higher V/Q ratio @ the top of the lungs

Question 14

Compensation for High V/Q Mismatch

Answer 14

Elevation of H+ causes hyperventilation => V/Q ratio rises in units w/o shunt

Question 15

PiO2

Answer 15

FeO2 (Pb-Patm)

Question 16

Va Equations

Answer 16

Va= freq (Vt-Vd)
Would need frequency of respiration, tidal volume, and dead space volume

Va= K (VCo2/PaCO2)
-This one is important for visualizing the relationship b/w PaCO2 and Va

Question 17

Measurement of lung compliance alone

Answer 17

Done by esophageal balloon technique

Question 18

Oxygen Capacity

Answer 18

Oxygen content-dissolved oxygen