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Flashcards in Oxygenation Deck (17):
1

What is the VCO2/VO2 ratio for the following:

carbohydrates

proteins

fats

carbohydrates = 1.0

proteins = 0.8

fats = 0.7

2

What is the normal PvO2 and saturation?

PVO2 is around 40-45 mmHg

saturation is around 100 mmHg

3

What is a normal A-a difference?

A-a difference = 2.5 + 0.25(age)

4

PF ratio

PaO2/FiO2

typically used to measure the severity of hypoxemia

regardless of FiO2, a P/F ratio of greater than 450 is generally viewed as normal

5

What does a swidened A-a difference suggest?

hypoxemia

6

What are the three main pathophysiologic states that cause hypoxemia?

shunt

low V/Q

diffusion limitation

7

shunts

intrapulmonary shunt (pus, water, blood, atelectasis)

right to left intracardiac shunt

ratio of ventilation to perfusion is zero in lung units that are not ventilated

8

Low V/Q

ventilation is decrease but not absent to perfused lung units (asthma attack or COPD)

Q is increased for a given V (as in pulmonary embolism)

increasing the fraction of inspired oxygen readily increases the PaO2

9

diffusion limitation

increased interstitial thickening such as in pulmonary fibrosis

decreased area available for diffusion as in emphysema

10

causes for lowered MVO2

low cardiac output

high oxygen consumption

anemia

low SaO2

11

oxygen delivery (DO2) equation

DO2 = CO x arterial oxygen content

DO2 = CO x [(1.34 x Hg x SaO2) + 0.003 x PaO2]

12

ScvO2

central venous oxygen saturation

measurement done through a central venous catheter via the internal jugular or subclavian vein

13

causes of hypoxemia that do no involve an elevated A-a difference

hypoventilation

low barometric pressure

low FiO2

low RQ ratio

14

hypoventilation

overdose of heroin suppresses respiration

decreases minute ventilation and acutely elevates PaCO2 to 60 mmHg

PAO2 drops to 75 mmHg

PaO2 in response drops to 68 mmHg

A-a difference is preserved, but hypoxemia results

15

treatment of hypoventilation from heroin overdose

increase minute ventilation with the drug naloxone

stop heroin use

16

low barometric pressure

decreased PB will explain lowered PAO2 and PaO2 values

17

low FiO2 (below 0.21)

rare but can occur in inhalation injuries/fires where other gases "dilute" the fraction of inspired oxygen