Hypoxemia: Difference between revisions

Latest revision as of 21:11, 17 May 2023

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 hemoglobin, 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 patients)

Causes

Hypoventilation
- Always associated with increased PaCO2
- Normal A-a gradient
Right-to-left shunt
- Occurs when blood enters the systemic arteries with out traversing ventilated lung
  - Occurs with pulmonary consolidation, atelectasis
- Hallmark is failure of arterial O2 levels to increase with supplemental O2 (increased A-a)
V/Q mismatch
- PE, pneumonia, asthma, COPD
- Improves with supplemental O2
- A-a gradient increased
Diffusion impairment
- Improves with supplemental O2
- A-a gradient increased
Low inspired O2
- Improves with 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
- Abdominal distension
- Anemia
- CO Poisoning
- Salicylate toxicity
- Diabetic ketoacidosis (DKA)
- Diaphragm injury
- Electrolyte abnormalities
- Epiglottitis
- Flail chest
- Hypotension
- Metabolic acidosis
- Pneumonia
- Pneumothorax/hemothorax
- Renal Failure
- Sepsis
- Toxic ingestion
Other Associated with ↓ Respiratory Effort

Non-Emergent

Evaluation

Management

Disposition

References

Authors:

@@ Line 2: / Line 2: @@
 *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)
+*Occurs in states of low CO, low hemoglobin, 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)
+***P(A-a)O2 = 145 – PaCO2 – PaO2 (normal is <10 in young, healthy patients)
-==Pathophysiology==
 ===Causes===
-#Hypoventilation
+*Hypoventilation
-##Always associated w/ increased PaCO2
+**Always associated with increased PaCO2
-##Normal A-a gradient
+**Normal A-a gradient
-#Right-to-left shunt
+*Right-to-left shunt
-##Occurs when blood enters the systemic arteries w/o traversing ventilated lung
+**Occurs when blood enters the systemic arteries with out traversing ventilated lung
-###Occurs with pulmonary consolidation, atelectasis
+***Occurs with pulmonary consolidation, atelectasis
-##Hallmark is failure of arterial O2 levels to increase w/ supplemental O2 (incr A-a)
+**Hallmark is failure of arterial O2 levels to increase with supplemental O2 (increased A-a)
-#V/Q mismatch
+*V/Q mismatch
-##PE, PNA, asthma, COPD
+**PE, pneumonia, asthma, COPD
-##Improves w/ supplemental O2
+**Improves with supplemental O2
-##A-a gradient increased
+**A-a gradient increased
-#Diffusion impairment
+*Diffusion impairment
-##Improves w/ supplemental O2
+**Improves with supplemental O2
-##A-a gradient increased
+**A-a gradient increased
-#Low inspired O2
+*Low inspired O2
-##Improves w/ supplemental O2
+**Improves with supplemental O2
-##A-a gradient normal
+**A-a gradient normal
 ===Compensation===
 #Increased minute ventilation
@@ Line 32: / Line 32: @@
 #Increased sympathetic tone
-==DDx==
+==Differential Diagnosis==
+{{SOB DDX}}
+==Evaluation==
+==Management==
+==Disposition==
 ==See Also==
-[[Hypercapnea]]
+*[[Shortness of breath]]
+*[[Hypercapnia]]
+*[[Post-hypoxic myoclonus]]
+==References==
+<references/>
-==Source==
-Tintinalli
-[[Category:Pulm]]
+[[Category:Pulmonary]]