Arterial Blood Gas (ABG)
| Test | Normal Range | Critical Values |
|---|---|---|
| pH | 7.35-7.45 | <7.35 (acidosis) or >7.45 (alkalosis) |
| PaO2 | 75-100 mm Hg | Low = hypoxemia |
| PaCO2 | 35-45 mm Hg | High = respiratory acidosis; Low = respiratory alkalosis |
| HCO3- | 22-29 mEq/L | High = metabolic alkalosis; Low = metabolic acidosis |
| SaO2 | 95-100% | <95% (hypoxemia) |
Clinical Significance
NCLEX Pattern
ABG questions usually test rapid recognition of which value is outside range, whether the disorder is respiratory or metabolic, and which finding requires immediate escalation.
Elevated PaCO2
- Indicates: respiratory-acidosis, hypoventilation-related carbon dioxide retention
- Nursing action: assess respiratory rate and work of breathing, notify provider, and support ventilation strategy
Decreased PaCO2
- Indicates: respiratory-alkalosis, excessive ventilation with carbon dioxide loss
- Nursing action: evaluate cause of hyperventilation and reassess serial blood gases
Elevated HCO3-
- Indicates: metabolic-alkalosis
- Nursing action: review fluid status and causes of hydrogen ion loss, then trend follow-up chemistry and ABG values
Decreased HCO3-
- Indicates: metabolic-acidosis
- Nursing action: assess renal function and perfusion, then monitor trend response to treatment
Related Labs
- basic-metabolic-panel - Provides bicarbonate and other electrolyte context for ABG interpretation.
- serum-potassium - Potassium shifts often accompany acid-base disturbances.
- serum-sodium - Sodium and water balance can influence overall fluid and acid-base status.