09-20-2021
Arterial Blood Gases
STEPS:
1. Determine whether acidemia or alkalemia is
present (check pH)
2. Determine the cause of acidemia or alkalemia
(pCO2 and HCO3)
3. Determine whether a mixed disorder is present
(compensation)
pH
pCO2
HCO3
PaO2
BE
O2 sat
NORMAL VALUES
Normal
Notes
7.35 - 7.45
↑ acidosis
(mean: 7.4)
↓ alkalosis
35 - 45
If abnormal, respiratory
22 - 26
If abnormal, metabolic
80 - 100
Hyper/Hypoxemia
+/- 2
Base excess / deficit
97 - 98%
STEP 1: pH CLASSIFICATION
 ↑ = alkalosis
 ↓ = acidosis
 Mean is 7.4
 Kapag mas mataas kahit kaunti sa 7.4,
consider na as alkalosis.
 < 7.2 = severe acidemia; fatal
 Alkalosis - irritability, arrythmia, convulsions
 Acidosis - drowsiness, lethargy, coma
STEP 2: RESPIRATORY OR METABOLIC?
 If abnormal pCO2 = problem is respiratory
 Baliktad ng interpretation
 ↑ acidosis
 ↓ alkalosis
 If abnormal HCO3 = problem is metabolic
 If both is abnormal, compute for compensation
to know if it is a mixed disorder.
Respiratory Acidosis
Respiratory Alkalosis
pH
↓
pCO2
↑
↓
Metabolic Acidosis
N or
Metabolic Alkalosis
N or
HCO3
↑
N or ↓
STEP 3: COMPENSATION
 Check pH again
 Partially compensated - hindi parin bumabalik sa
normal range ang pH
 Fully compensated - naibalik sa normal ang pH
(normal pH but either > or < 7.4)
 Uncompensated - malayo sa normal range
STEP 4: CHECK PaO2
PaO2
Interpretation
> 100
Hyperoxemia
80 - 100
Normoxemia
60 - 79
Mild Hypoxemia
40 - 59
Moderate Hypoxemia
< 40
Severe Hypoxemia
EXAMPLES:
1. pH 7.3 | PaCO2 68 | HCO3 28 | PaO2 60
Answer: Partially compensated respiratory
acidosis with mild hypoxemia
2. pH 7 | PaCO2 23 | HCO3 12 | PaO2 90
Answer: Partially compensated metabolic
acidosis
3. pH 7.6 | PaCO2 31 | HCO3 25 | PaO2 120
Answer: Uncompensated respiratory alkalosis
with hyperoxemia
4. pH 7.5 | PaCO2 40 | HCO3 34 | PaO2 85
Answer: Uncompensated metabolic
alkalosis
5. pH 7.10 | PaCO2 70 | HCO3 24 | PaO2 90
Answer: Uncompensated respiratory
acidosis
6. pH 7.39 | PaCO2 27 | HCO3 19 | PaO2 123
Answer: Fully compensated metabolic
acidosis with hyperoxemia
7. pH 7.525 | PaCO2 36 | HCO3 31 | PaO2 273
Answer: Uncompensated metabolic
alkalosis with hyperoxemia
CAUSES
Common Causes
Respiratory failure due to
illness or any other cause
(e.g. asthma, inadequate
mechanical ventilation, CNS
depression
Respiratory Alkalosis Hyperventilation
Excessive mech ventilation
Metabolic Acidosis
Severe gastroenteritis
Diabetic ketoacidosis
Shock: hypovol.., cardiogenic
Perinatal Asphyxia
Metabolic Alkalosis
Pyloric stenosis
Diuretics
Excessive NGT losses
Disorder
Respiratory Acidosis
TREATMENT
 Respiratory Acidosis
 Treat undelrying etiology, antibiotic for
pneumonia, supplemental oxygen, mechanical
ventilation (to reverse hypoxia)
 Respiratory Alkalosis
 Treat underlying cause, mechanical ventilator
settings
adjustment,
rebreathing,
Benzodiazepines
 Metabolic Acdosis
 Repair
underlying
disorder,
HCO3,
hemodialysis
 Metabolic Alkalosis
 Address
underlying
pathology,
discontinue/reduce diuretics, Na and K
replacement