From the Guidelines
The normal ranges for arterial partial pressure of carbon dioxide (PCO2) and partial pressure of oxygen (PO2) are 4.6–6.1 kPa (34–46 mm Hg) and 10.0-13.3 kPa (75-100 mm Hg), respectively.
Normal Ranges for PCO2 and PO2
- The normal range for PCO2 is 4.6–6.1 kPa (34–46 mm Hg), as stated in the BTS guideline for oxygen use in adults in healthcare and emergency settings 1.
- The normal range for PO2 is 10.0-13.3 kPa (75-100 mm Hg), which can be inferred from the normal range of 75-100 mm Hg for young adults 1.
Key Points
- PCO2 levels are controlled by chemical sensors in the carotid body and brainstem, and are carried in the blood in three forms: bicarbonate, dissolved carbon dioxide, and bound to haemoglobin 1.
- PO2 levels are expressed in terms of oxygen saturation (SaO2 or SpO2) or partial pressure of oxygen (PaO2) 1.
- Hypercapnia (elevated PCO2 levels) can occur when there is decreased effective or 'alveolar' ventilation, and can be avoided by giving targeted lower concentration oxygen therapy to vulnerable patients 1.
From the Research
Normal Ranges for Arterial Partial Pressure of Carbon Dioxide (PCO2) and Partial Pressure of Oxygen (PO2)
- The normal range for arterial partial pressure of carbon dioxide (PaCO2) is approximately 35-45 mmHg 2, 3, 4.
- The normal range for partial pressure of oxygen (PO2) is approximately 75-100 mmHg 3, 5, 6.
Factors Affecting PCO2 and PO2 Levels
- Cardiac output can affect PaCO2 levels, with central venous Pco2 exceeding the arterial value by approximately 4 mm Hg when cardiac output is relatively normal 2.
- Lung disease and ventilator settings can affect the accuracy of end-tidal Pco2 (PetCO2) measurements, which can sometimes seriously underestimate the arterial value 2.
- Arterialized earlobe blood samples can be used to estimate PaCO2, but may not be reliable for estimating PO2 3.
- Regional differences in PO2 and PCO2 can occur, such as in the pulmonary "wedge" samples of blood, which can have higher PO2 and lower PCO2 values than peripheral arterial blood 5.
- Tidal volume and positive end-expiratory pressure (PEEP) level can affect the partial pressure of oxygen and carbon dioxide in perfluorocarbon liquid during partial liquid ventilation 6.
Clinical Implications
- High PaCO2 levels can cause decreased peripheral tissue and visceral organ perfusion through the autonomic nervous system in patients with respiratory failure undergoing pressure support ventilation with veno-venous extracorporeal membrane oxygenation (V-V ECMO) 4.