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21 Cards in this Set
- Front
- Back
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what indicates adequate oxygenation
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O2 sat > 90%
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O2:Hgb dissociation curve
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S curve
dramatic increase in O2 sat at certain PO2 concentration at about PO2 55, 90% O2 sat at about PO2 90, 97% O2 sat dramatic O2 sat change from 45-55 PO2 |
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adequacy of oxygenation
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is oxygenation good enough?
measured O2 sat > 90%? |
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efficiency of oxygenation
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is oxygenation working as expected?
for room air FO2 = 0.21 - is A-a pO2 normal? for high FO2 (>0.21) - is PaO2/FiO2 high? - normal is >425 |
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measures of oxygenation efficiency
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alveolar-arterial gradient
PaO2/FiO2 P to F ratio |
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A-a gradient
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normal A-a = age/4
- lung is not cause of low PaO2 wide A-a - impaired oxygenation - usually lung problem (rarely cardiac R to L shunt) |
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P to F ratio
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use for FiO2 > 0.21 (high FiO2=supplemental O2)
normal >425 good >300 problematic oxygenation 200-300 really bad hypoxemia <200 tells mild, moderate or severe acute respiratory distress |
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A-a gradient calculation
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PAO2 calculated from Pbar & PaCO2
= F,O2 (Pbar-Pwater) - PACO2 = 0.21 (760-47) - PaCO2/R PaCO2/R = 40/0.8 = 50 = 150-50 = 100 (at sea level) PaO2 measured on ABG (ex. 90) A-a = 100-90 = 10 - normal for 40 yr old bar P lower in denver |
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what type of hypoxemia minimally responsive to supplemental O2 therapy
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shunt
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clinical cataegorization of hypoxemia
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hypoventilation: normal A-a gradient
- improves with supplemental O2 - narcotics: CO2 rises & PaO2 falls; not lung problem decrease V/Q: moderate increase in A-a gradient - improves with sup O2 - asthma, COPD, mild HR - lung loading problem; put more P in to decrease gradient shunt: large increase in gradient - no change with sup O2 - air doesn't see O2 b/c alv. filled diffusion: small increase with gradient; esp with exercise - improves with sup O2 - not enough time for O2 o move into blood; reduce time by increasing CO2 - less time in lung for Oxygen; unmask diffusion prob with exercise (walk and desat) |
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V/Q matching 2 compartments
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air
- delivers O2 to alveolus - air space diseases: impaired oxygen loading blood - delivers CO2 to alveolus - vascular diseases: impaired CO2 unloading |
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shunt
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airspace disease
physiology: zero V/Q ABG: refractory hypoxemia hx: SOB, cyanosis exam: diffuse crackles (alv full) radiograph: white out |
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examples of shunt
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acute resp distress syndrome
severe carrdiac pulmonary edema (MI) |
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16 yo male blue and combative; normal acid base; normal ventilation via PaCO2; severe hypoxemia by low PaO2; inadequate oxygenation by O2 sat; wide A-a gradient; super low P:F
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hypoxemia due to shunting
R-to-L shunting from aspiration & trauma= ARDS supp O2 had almost no effect lung function grossly abnormal solution - tx infection with anttibiotics - open up alveoli with mechanical ventilator - wait until gets better |
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low V/Q
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not 0, like shunt
airspace disease physiology: decreased V/Q ABG: reversible hypoxemia hx: cough, SOB exam: few crackles radiograph: focal whiteness (lobar pneumonia) |
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examples of low V/Q
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lobar pneumonina
early pulmonary edema (patchy with HF) mild alveolar hemorrhage |
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36 yo female SOB, fever & cough; normal acid base; normal ventilation via PaCO2; mild hpoxemia via PaO2; inadequate oxygenation via O2 sat; wide gradient
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hypoxemia due to low V/Q
PaO2 inadequate b/c of lobar pneumonia lung function abnormal : wide gradient solution: - antibiotics - supplemental O2 |
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what disorders are due to pulmonary vascular disease
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PE
emphysema (loss of caps make you need O2) primary pulmonary HTN |
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pulmonary vascular disease work up
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physiology (dead space): increase V/Q & increase minute vol
ABG: decrease PaO2; mild; PaO2 improves with sup O2 Hx: dyspnea on exertion Radiograph not white (too black = emphysema) |
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42 yo male SOB & sore leg; acute respiratory alkalosis; PaCO2 shows hyperventilation; PaO2 shows mild hypoxemia; O2 sat shows adequate oxygenation; gradient wide
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hypoxemia from low V/Q due to PE
- PaO2 adequate b/c hyperventilation - lung function abnormal: wide gradient PaCO2 could either be - high due to dead space of PE impairing CO2 excretion; seen in elderly and weaker pts - low b/c PE stimulates breathing and enhances CO2 excretion; seen in younger solution: - pulmonary angiogram to see clots - Rx: IV heparin & supp O2 ; mild sup O2 usually corrects hypoxemia of PE |
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16 yo male brought to ER unconscious; acute resp acidosis; PaCO2 shows hypoventilation; PaO2 shows mild hypoxemia; O2 sat shows inadequate oxygenation; gradient normal
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hypoventilation: acidosis & hypoxemia
depressed brain activit: heroin OD lung function normal : normal gradient solution - mechanical ventilation - narcotic antagonist to restore resp drive |
