The partial pressure of carbon dioxide (PaCO2) in arterial blood is an indicator of health that shows how well the lungs are removing carbon dioxide. As a waste product of the body’s metabolism, its level reflects respiratory function. PaCO2 also plays a large part in maintaining the body’s acid-base balance.
Measuring PaCO2 and Its Role in the Body
PaCO2 is measured with an Arterial Blood Gas (ABG) test, which involves drawing blood from an artery. Arterial blood provides an accurate picture of respiratory efficiency. An ABG test also assesses oxygen (PaO2), blood pH, and bicarbonate levels for a comprehensive view of a patient’s respiratory and metabolic state.
Carbon dioxide, a byproduct of metabolism, is transported in the blood to the lungs to be exhaled. In the bloodstream, CO2 acts as an acid, and the amount present directly influences the body’s pH balance. The normal range for PaCO2 is between 35 and 45 mmHg.
High PaCO2 Levels (Hypercapnia)
High PaCO2 levels, or hypercapnia, cause increased blood acidity, a state called respiratory acidosis. The condition results from hypoventilation, which is breathing that is too shallow or slow to meet the body’s needs.
Hypoventilation can be caused by several conditions. Chronic lung diseases like COPD impair the lungs’ ability to exhale fully, while acute issues like a severe asthma attack can interfere with gas exchange. Other causes include nervous system depression from an opioid overdose or neuromuscular disorders like ALS. Symptoms of hypercapnia include shortness of breath, headaches, confusion, and lethargy.
Low PaCO2 Levels (Hypocapnia)
Low PaCO2 levels, or hypocapnia, result from hyperventilation (breathing too fast or deep). This expels carbon dioxide too quickly, leading to decreased blood acidity, known as respiratory alkalosis.
Hyperventilation can be triggered by anxiety, panic attacks, severe pain, or fever. It can also be caused by exposure to high altitudes or medical conditions like a pulmonary embolism.
Symptoms of hypocapnia relate to the effects of alkalosis on the nervous system. These include dizziness, lightheadedness, muscle cramps, and a tingling sensation in the hands, feet, and around the mouth.
Clinical Interpretation and Treatment
An abnormal PaCO2 level indicates an underlying issue, not a disease itself. Physicians interpret the value with other ABG results, like pH and bicarbonate, to find the root cause. This analysis determines if the problem is respiratory or involves metabolic factors.
Treatment focuses on the underlying condition. For high PaCO2 from a COPD flare-up, interventions improve lung function. For low PaCO2 from a panic attack, treatment involves helping the person slow their breathing rate to restore normal levels.