Carbon Dioxide (CO2) in Blood

Carbon dioxide (CO2) is a colorless, odorless gas that is present in the blood. It is a byproduct of cellular metabolism and is transported from the tissues to the lungs, where it is exhaled.

Measurement of CO2 in Blood

The level of CO2 in blood is typically measured through a blood test called an arterial blood gas (ABG) analysis. This test measures the partial pressure of CO2 (PaCO2) in arterial blood, which reflects the amount of CO2 being transported from the tissues to the lungs.

Normal Values

The normal range for PaCO2 is between 35-45 mmHg. A level above 45 mmHg indicates hypercapnia (elevated CO2), while a level below 35 mmHg indicates hypocapnia (reduced CO2).

Functions of CO2 in Blood

CO2 plays several important roles in the body, including:

• Regulation of pH balance: CO2 helps to regulate the body's acid-base balance by reacting with water to form carbonic acid, which then dissociates into hydrogen ions and bicarbonate.
• Transportation of oxygen: CO2 binds to hemoglobin in red blood cells, forming carbaminohemoglobin, which helps to transport oxygen from the lungs to the tissues.
• Stimulation of breathing: An increase in PaCO2 stimulates the respiratory centers in the brain, leading to an increase in ventilation and helping to regulate breathing.

Abnormalities in CO2 Levels

Abnormal levels of CO2 in blood can indicate various medical conditions, including:

• Respiratory acidosis: Elevated PaCO2 due to respiratory failure or hypoventilation.
• Respiratory alkalosis: Reduced PaCO2 due to hyperventilation or respiratory stimulation.
• Metabolic acidosis: Elevated anion gap due to increased production of acidic substances, such as lactic acid or ketones.
• Metabolic alkalosis: Reduced anion gap due to loss of acidic substances, such as through vomiting or nasogastric suction.

Clinical Significance

Measuring CO2 levels in blood is important for diagnosing and managing various medical conditions, including respiratory and metabolic disorders. It can also help to guide treatment decisions, such as the need for mechanical ventilation or adjustments to medication regimens.