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NURO 670 Final - Acid Base Balances And ABGs Exam Latest Update
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NURO 670 Final - Acid BaseBalances And ABGs Exam Latest
Update
A-a gradient - Answer partial pressure of alveolus compared to O2 diffusion
normal 5-15.
abnormal = diffusion defect, v/q mismatch, R to L shunt
P/F ratio - Answer PaO2/FiO2 = PF ratio
normal >300-500
200-300 = ALI/dmg
ARDS = <200 (or actually severe ARDS= <100)
mechanisms of hypoxemia - Answer - low inspired O2
- hypoventilation
- diffusion impairment
- vent/perfusion mismatch
- shunting
causes of hypoventilation - Answer - CNS depression
- neural conduction disorders
- muscular weakness
- diseases of chest wall
diffusion impairment causes - Answer - total surface area for gas exchange =
alveolar/cap membranes
- tissue issues - scarring/fibrosis
- fluid - pulm edema
vent/perfusion mismatch causes - Answer - hypoxemia because of imbalance of blood
flow/ventilation
, - hypoxemia bc of v/q mismatch (responds to low/moderate supplemental O2)
vent/perfusion physiology and mismatch - Answer decrease ventilation to perfusion -
SHUNTING
underventilated alveoli = deoxygenated blood back to heart
commonly: atelectasis, PNA, pulm edema.
decrease in perfusion to ventilation - DEADSPACE
adequate vent of alveoli but without good perfusion
commony: PE, shock
intrapulmonary shunting - Answer shunting = blood w/o oxygenation
- NOT responsive to O2 supplement
- ex: ARDS, atelectasis, PE, PNA, pulm edema, vascular lung tumors, intracardiac R to L
shunt (VSDs)
- anatomic shunting - natural - ex: bronchiole and coronary arteries
where does SaO2 and PaO2 drop on oxyhemoglobin curve? - Answer 90% and 60mmHg
what causes LEFT shift on oxyhemoglobin curve? - Answer - HYPO thermia
- alkalosis
- decrease 2,3 DPG
- low PaCO2
**HIGHER affinity for O2, holds onto it more
what causes RIGHT shift on oxyhemoglobin curve? - Answer - HYPER thermia
- acidosis
- increased 2,3 DPG
- high PaCO2
**LOWER affinity for O2, releases easier (hypermetabolic state= need more O2)
caution with L / R shift on oxyhemogb curve with what?? - Answer L shift - SaO2 can be
good, but still hypoxemic
R shift - compensatory mechanism due to increase of metabolic demands. beware of
hypermetabolic state
main indicator of ventilation - Answer CO2
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