ABG Quick Reference
Arterial blood gas values and a step-by-step way to read them.
CARE Nursing · carenursingprep.com
ABG Quick Reference
Values
Taken from the same verified dataset as CARE's lab-values reference.
| pH, arterial | 7.38–7.44Sources differ: This is the value most worth understanding. ABIM's exam sheet gives 7.38–7.44; nursing teaching almost universally uses 7.35–7.45. Neither is wrong — they are different reference populations and methods — but a student taught 7.35 as a hard boundary will mis-read an item built on the narrower range. |
|---|---|
| PaCO₂, arterial | 38–42 mm HgSources differ: ABIM gives 38–42 mm Hg; nursing convention teaches 35–45. |
| PaO₂, arterial | 75–100 mm Hg |
| Bicarbonate (HCO₃⁻), arterial | 23–26 mEq/LSources differ: ABIM lists arterial bicarbonate as 23–26 mEq/L and serum bicarbonate separately — legitimately, because they are different specimens and methods. A single 'bicarbonate' row that ignores the specimen is hiding a real distinction. |
| Oxygen saturation, arterial | ≥95 % |
How to read a gas
| 1. Look at pH | Below range = acidosis · above range = alkalosisIf pH is inside the range but the other values are not, compensation is happening. |
|---|---|
| 2. Look at PaCO₂ | Moves OPPOSITE to pH ⇒ respiratory causeCO₂ is an acid: more CO₂ means lower pH. |
| 3. Look at HCO₃⁻ | Moves WITH pH ⇒ metabolic causeBicarbonate is a base: more bicarbonate means higher pH. |
| 4. Compensation | The other system moves to pull pH backUncompensated: pH abnormal, one system normal. Partially: all abnormal, pH still out. Fully: pH back in range, others still abnormal. |
| 5. Oxygenation | Read PaO₂ separatelyOxygenation is a distinct question from acid–base status. |
Educational reference. ABG reference limits differ between sources — ABIM gives arterial pH 7.38–7.44 where nursing teaching commonly uses 7.35–7.45. Interpret real results against the reporting laboratory's own ranges.