Total CO2, a measurement often seen in blood tests, provides insight into the body’s acid-base balance. This balance reflects how well the body’s systems, particularly the kidneys and lungs, manage acidic and basic compounds. Deviations in total CO2 levels can signal underlying health issues that warrant medical attention.
Understanding Total Carbon Dioxide in the Body
Total CO2 in a medical test primarily measures bicarbonate (HCO3-), which accounts for 90% to 95% of the total carbon dioxide in the blood. Bicarbonate is an electrolyte, a negatively charged ion that helps maintain the acid-base balance, or pH, of the body’s fluids. The normal range for total CO2 in adults is between 23 and 29 milliequivalents per liter (mEq/L), though this can vary between laboratories.
The bicarbonate-carbonic acid buffer system is a primary mechanism for maintaining blood pH within a narrow range of 7.35-7.45. When excess acid enters the bloodstream, bicarbonate ions neutralize it by accepting hydrogen ions, forming carbonic acid. Conversely, if the blood becomes too alkaline, carbonic acid releases hydrogen ions to restore balance. Both the lungs, by regulating carbon dioxide elimination, and the kidneys, by controlling bicarbonate reabsorption or excretion, can regulate its components.
Common Causes of Low Total Carbon Dioxide Levels
Low total CO2 levels, also known as hypocarbia or hypocapnia, indicate an underlying acid-base imbalance, typically metabolic acidosis. Metabolic acidosis occurs when too much acid builds up in the body or when there is an excessive loss of bicarbonate. One common cause is diabetic ketoacidosis (DKA), a severe complication of diabetes where a lack of insulin causes the body to break down fats for energy, producing acidic ketone bodies. These ketones consume bicarbonate, leading to a reduction in its concentration in the blood.
Kidney disease can also lead to low total CO2 levels because impaired kidneys may not effectively excrete acids or reabsorb bicarbonate, leading to an accumulation of acid in the blood. As kidney function declines, the prevalence of metabolic acidosis increases. Severe diarrhea is another cause, as the intestines normally secrete bicarbonate, and excessive fluid loss through diarrhea can deplete the body’s bicarbonate stores.
Lactic acidosis results from an accumulation of lactic acid due to insufficient oxygen supply to tissues or impaired lactate metabolism. Conditions such as severe infections (sepsis), heart failure, or prolonged lack of oxygen can lead to increased lactate production, which consumes bicarbonate and lowers total CO2. Certain medications can also contribute to low total CO2. For instance, some carbonic anhydrase inhibitors can reduce bicarbonate reabsorption in the kidneys, leading to its loss. Aspirin overdose (salicylate toxicity) can directly stimulate the respiratory center, leading to hyperventilation and a decrease in carbon dioxide, and can also cause metabolic acidosis.
Recognizing Symptoms and Health Implications
Low total CO2 levels can manifest through various symptoms, which often reflect the underlying cause or the body’s attempt to compensate for the acid-base imbalance. Common symptoms include rapid and deep breathing, known as Kussmaul breathing, as the body tries to expel more carbon dioxide to reduce acidity. Individuals may also experience confusion, fatigue, and weakness. Nausea and vomiting are common.
As the imbalance progresses, symptoms can become more severe, including dizziness, lightheadedness, numbness, and tingling sensations, especially in the hands and feet. Muscle cramps and spasms may also occur due to changes in pH affecting muscle function. In severe cases, particularly with metabolic acidosis, altered mental status, reduced organ function, or even shock can develop. Prolonged metabolic acidosis can lead to serious health consequences, such as the thinning of bones (osteoporosis). It can also contribute to muscle weakness and loss, impair growth in children by suppressing growth hormone release, and worsen existing kidney disease.
Diagnosis and Treatment Approaches
The diagnosis of low total CO2 primarily involves a blood test, commonly part of an electrolyte panel or a basic metabolic panel. This test measures the total carbon dioxide in the blood, which largely represents bicarbonate levels. If the total CO2 level is found to be below the normal range (less than 22 mEq/L), further investigation, including an arterial blood gas (ABG) test, may be conducted to understand the blood’s pH and gas levels more precisely. A comprehensive medical history and physical examination also help pinpoint the underlying cause.
Treatment for low total CO2 focuses on addressing the root cause of the acid-base imbalance rather than solely attempting to increase CO2 levels. For conditions like diabetic ketoacidosis, treatment involves intravenous fluids to correct dehydration, insulin therapy to manage high blood sugar and stop ketone production, and electrolyte replacement to restore balance. In cases of severe acidosis, sodium bicarbonate may be administered intravenously, but its use is carefully considered due to potential risks.
For metabolic acidosis caused by severe diarrhea, treatment emphasizes fluid and electrolyte replacement, using oral rehydration solutions or intravenous fluids for severe dehydration. If kidney disease is the cause, management may include dietary modifications, medications to help the kidneys excrete acids, or dialysis in advanced stages. Continuous monitoring of vital signs, electrolytes, and acid-base status is performed throughout treatment to ensure safe and effective correction of the imbalance.