Is a pCO2 of 43 mmHg Normal?
Yes, a pCO2 of 43 mmHg is within the normal reference range and does not require intervention in most clinical contexts. 1
Normal Reference Range
The established normal range for arterial carbon dioxide tension (PaCO2) is 34-46 mmHg (4.6-6.1 kPa) in healthy adults, as defined by international consensus guidelines and the American Thoracic Society. 1
The 2024 international consensus similarly defines normocapnia as 35-45 mmHg, with your value of 43 mmHg falling comfortably within this range. 1
Minor variations between laboratories exist but typically remain within 0.2 kPa of the standard range, so a value of 43 mmHg is consistently considered normal across all reference standards. 1
Clinical Interpretation
A pCO2 of 43 mmHg indicates normal ventilatory function and appropriate carbon dioxide clearance. 2
This value sits in the middle-to-upper portion of the normal range, suggesting adequate alveolar ventilation without hypoventilation or hyperventilation. 2
PaCO2 should always be interpreted alongside pH and bicarbonate levels to fully assess acid-base status, but an isolated value of 43 mmHg alone is reassuring. 1
Context-Specific Considerations
While 43 mmHg is normal in most situations, certain clinical contexts require additional scrutiny:
In Acute Asthma Exacerbations
- A "normal" PaCO2 (like 43 mmHg) in a breathless asthmatic patient is actually a marker of severe, life-threatening attack, as these patients should be hyperventilating with low PaCO2 values. 1
- This represents a critical pitfall where a seemingly normal value indicates impending respiratory failure and may require ICU transfer with preparation for intubation. 1
In Chronic Lung Disease
- Patients with COPD typically have elevated PaCO2 in the range of 45-55 mmHg, so 43 mmHg would be considered excellent control or indicate early disease. 1
- In contrast, patients with interstitial lung disease or pulmonary vascular disease typically have PaCO2 of 30-35 mmHg due to compensatory hyperventilation, making 43 mmHg relatively elevated for these conditions. 1
In Post-Cardiac Arrest Care
- Targeting normocapnia (35-45 mmHg) is specifically recommended, making 43 mmHg an ideal target value. 1
Bottom Line
For the vast majority of clinical scenarios, a pCO2 of 43 mmHg represents normal respiratory function and requires no intervention. 1 The key is ensuring this value is interpreted in the appropriate clinical context, particularly watching for the dangerous scenario of a "normal" pCO2 in an acutely breathless patient who should be hyperventilating. 1