Hypoxemia: Difference between revisions
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***P(A-a)O2 = 145 – PaCO2 – PaO2 (normal is <10 in young, healthy pts) | ***P(A-a)O2 = 145 – PaCO2 – PaO2 (normal is <10 in young, healthy pts) | ||
===Causes=== | ===Causes=== | ||
#Hypoventilation | #Hypoventilation | ||
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##Improves w/ supplemental O2 | ##Improves w/ supplemental O2 | ||
##A-a gradient normal | ##A-a gradient normal | ||
===Compensation=== | ===Compensation=== | ||
#Increased minute ventilation | #Increased minute ventilation | ||
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#Increased sympathetic tone | #Increased sympathetic tone | ||
== | ==Differential Diagnosis== | ||
{{SOB DDX}} | |||
==Diagnosis== | |||
==Management== | |||
==See Also== | ==See Also== | ||
Revision as of 19:23, 11 May 2015
Background
- Defined as PaO2 <60 mm Hg
- Amount of oxygen available is a function of the arterial oxygen content and blood flow
- Occurs in states of low CO, low Hb, or low SaO2 (arterial oxygen saturation)
- Relative Hypoxemia
- PaO2 is < expected for given level of inhaled O2 (e.g. PaO2 of 100 on FiO2 100%)
- Can calculate amount of relative hypoxemia by A-a gradient
- P(A-a)O2 = 145 – PaCO2 – PaO2 (normal is <10 in young, healthy pts)
Causes
- Hypoventilation
- Always associated w/ increased PaCO2
- Normal A-a gradient
- Right-to-left shunt
- Occurs when blood enters the systemic arteries w/o traversing ventilated lung
- Occurs with pulmonary consolidation, atelectasis
- Hallmark is failure of arterial O2 levels to increase w/ supplemental O2 (incr A-a)
- Occurs when blood enters the systemic arteries w/o traversing ventilated lung
- V/Q mismatch
- PE, PNA, asthma, COPD
- Improves w/ supplemental O2
- A-a gradient increased
- Diffusion impairment
- Improves w/ supplemental O2
- A-a gradient increased
- Low inspired O2
- Improves w/ supplemental O2
- A-a gradient normal
Compensation
- Increased minute ventilation
- Pulmonary arterial vasoconstriction
- Increased sympathetic tone
Differential Diagnosis
Acute dyspnea
Emergent
- Pulmonary
- Airway obstruction
- Anaphylaxis
- Angioedema
- Aspiration
- Asthma
- Cor pulmonale
- Inhalation exposure
- Noncardiogenic pulmonary edema
- Pneumonia
- Pneumocystis Pneumonia (PCP)
- Pulmonary embolism
- Pulmonary hypertension
- Tension pneumothorax
- Idiopathic pulmonary fibrosis acute exacerbation
- Cystic fibrosis exacerbation
- Cardiac
- Other Associated with Normal/↑ Respiratory Effort
- Other Associated with ↓ Respiratory Effort
Non-Emergent
- ALS
- Ascites
- Uncorrected ASD
- Congenital heart disease
- COPD exacerbation
- Fever
- Hyperventilation
- Interstitial lung disease
- Neoplasm
- Obesity
- Panic attack
- Pleural effusion
- Polymyositis
- Porphyria
- Pregnancy
- Rib fracture
- Spontaneous pneumothorax
- Thyroid Disease
- URI
Diagnosis
Management
See Also
Source
Tintinalli