Normal value of pCO2 and bicarbonate value in blood
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Here is a complete, textbook-confirmed summary of normal pCO2 and bicarbonate values in blood:
Normal Blood Gas Values: pCO2 and Bicarbonate
pCO2 (Partial Pressure of Carbon Dioxide)
| Sample Type | Normal Range | Mean |
|---|---|---|
| Arterial (PaCO2) | 35-45 mmHg | 40 mmHg |
| Venous (PvCO2) | 45-51 mmHg | ~46 mmHg |
- Roberts and Hedges' Clinical Procedures in Emergency Medicine confirms: respiratory acidosis is defined as pCO2 > 45 mmHg, and respiratory alkalosis as pCO2 < 35 mmHg - with 35-45 mmHg being the normal corridor.
- In SI units: arterial pCO2 = 4.7-6.0 kPa (per Henry's Clinical Diagnosis and Management by Laboratory Methods).
Bicarbonate (HCO3-)
| Parameter | Normal Range | Mean |
|---|---|---|
| Arterial HCO3- | 22-26 mEq/L | 24 mEq/L |
| Serum/venous HCO3- | 22-29 mmol/L | ~24 mmol/L |
- Guyton and Hall Textbook of Medical Physiology lists: HCO3- average = 24 mmol/L, range = 22-29 mmol/L.
- Metabolic acidosis is diagnosed when HCO3- falls < 22 mEq/L; metabolic alkalosis when it rises above normal.
Full ABG Normal Values (for context)
| Parameter | Normal Value |
|---|---|
| pH (arterial) | 7.35-7.45 (mean 7.40) |
| PaCO2 | 35-45 mmHg |
| PaO2 | 80-100 mmHg |
| HCO3- | 22-26 mEq/L |
| Base excess (BE) | -2 to +2 mEq/L |
| O2 saturation | 95-100% |
Acid-Base Pattern Quick Reference
| Disorder | pH | HCO3- | pCO2 |
|---|---|---|---|
| Metabolic acidosis | Low (<7.40) | Low | Low (compensatory) |
| Metabolic alkalosis | High (>7.40) | High | High (compensatory) |
| Respiratory acidosis | Low (<7.40) | High (compensatory) | High (primary) |
| Respiratory alkalosis | High (>7.40) | Low (compensatory) | Low (primary) |
(Table 9.4 - Henry's Clinical Diagnosis and Management by Laboratory Methods)
Key clinical memory aids:
- pCO2: "35-45" - the lungs keep it here; any value outside = respiratory disturbance or compensation
- HCO3-: "22-26" (or loosely 24 ± 2) - the kidneys regulate this; any value outside = metabolic disturbance or renal compensation
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