Normal Adult Venous Blood Gas Levels
Normal venous blood gas values in healthy adults are: pH 7.30-7.43, PO2 19-70 mmHg (or 25-70 mmHg), PCO2 35-59 mmHg (or 38-58 mmHg), and bicarbonate 22-30 mmol/L. 1, 2
Core Parameters
The most recent prospective studies establishing venous blood gas reference intervals provide the following normal ranges:
- pH: 7.30-7.43 (venous pH is approximately 0.03 units lower than arterial pH) 1, 3
- PCO2: 35-59 mmHg or 38-58 mmHg (venous PCO2 is approximately 4-6 mmHg higher than arterial) 1, 2
- PO2: 19-70 mmHg or 25-70 mmHg (venous PO2 is significantly lower than arterial, approximately 40 mmHg lower) 1, 2
- Bicarbonate (HCO3-): 22-30 mmol/L 1, 2
- Base Excess: -1.9 to +4.5 mmol/L 1
Electrolyte Values
Normal venous blood gas electrolyte ranges include:
- Sodium: 134-144 mmol/L 1, 2
- Potassium: 3.1-4.6 mmol/L or 3.6-4.5 mmol/L 1, 2
- Chloride: 101-110 mmol/L 1, 2
- Ionized Calcium: 1.12-1.30 mmol/L or 1.14-1.29 mmol/L 1, 2
Additional Parameters
- Lactate: 0.4-2.2 mmol/L 1
- Oxygen Saturation (sO2): 23-93% 1
- Carboxyhemoglobin: 0.4-1.4% 1
- Methemoglobin: 0.3-0.9% 1
Comparison to Arterial Values
For reference, normal arterial blood gas values (room air) are: PO2 >90 mmHg, PCO2 <40 mmHg, and pH 7.40. 3 Normal mixed venous blood (room air) shows: PO2 40 mmHg, PCO2 50 mmHg, and pH 7.35. 3
Clinical Considerations
The key difference between venous and arterial samples is the PO2, which shows poor agreement and cannot be used interchangeably. 4 Venous pH, bicarbonate, and base excess have sufficient agreement with arterial values to be clinically interchangeable in non-shocked patients. 4 However, venous PCO2 has wide limits of agreement (±20 mmHg) and should only be used for screening hypercarbia or monitoring trends, not as a one-off replacement for arterial PCO2. 4
A critical pitfall is attempting to use venous blood gas in patients with severe metabolic acidemia or shock, where the venous-to-arterial conversion methods may be unreliable. 5 In one case, a patient with arterial pH 7.07 had a calculated pH of 7.42 using conversion software, demonstrating dangerous inaccuracy in severe acidosis. 5