Evaluating Patients with Hypoxemia Flashcards
what is considered cyanosis (measured value)?
increase in the deoxygenated hemoglobin level to above 5g/dL
(normal Hgb = 13.5-15 g/dL)
What’s measurements are obtained from arterial blood gas vs pulse oximeter?
arterial blood gas: PaO2 and SaO2 (saturation)
pulse oximeter: SpO2 (saturation)
how does anemia affect the O2 content of the blood?
decreased O2 content
how does CO poisoning affect the O2 content of the blood?
decreased
how does methemoglobinemia affect the O2 content of the blood?
decreased
[methemoglobin = iron in oxidized ferric form, Fe3+ —> unable to bind O2, dissociation curve shifted LEFT]
What is a normal A-a gradient?
A-a gradient compares the arterial oxygen tension (PaO2) to the alveolar oxygen tension (PAO2)
normal = 8-10mmHg
how will hypoventilation affect the A-a gradient?
it won’t - hypoventilation is an important cause of normal A-a gradient hypoxemia
decreased PAO2 —> decreased PaO2 —> decreased SaO2
which of the following will NOT present with an increased A-a gradient?
a. low V/Q ratio
b. hypoventilation
c. intrapulmonary shunt
d. impaired diffusion
b. hypoventilation - normal A-a gradient
low V/Q ratio, impaired diffusion, and intrapulmonary shunt (increased R to L shunt) will cause INCREASED A-a gradient
If a patient’s partial pressure of oxygen does not change significantly with supplemental oxygen, what is the most likely cause of their hypoxemia?
most likely an intrapulmonary shunt (functional pulmonary capillaries are already extracting the max amount of oxygen)
which of the following conditions will not show a significant response to supplemental oxygen?
a. COPD
b. ARDS
c. interstitial lung disease
b. ARDS - shunt, will not respond to supplemental O2
a. COPD - V/Q mismatch
c. interstitial lung disease - diffusion impairment
