A finding of low carbon dioxide (CO2) in the blood on a lab test points to an underlying imbalance within the body’s regulatory systems. This condition, medically termed hypocapnia, is not a disease itself but rather a sign that something has disrupted the normal exchange of gases. It indicates that the level of CO2, a waste product of the body’s metabolic processes, has fallen below the typical range. This shift can alter the blood’s delicate chemical environment.
The Role of Carbon Dioxide in the Body
While often seen as a waste product, carbon dioxide is a highly regulated substance in the bloodstream that performs important functions. The body’s metabolic activities, such as converting food into energy, constantly produce CO2. This gas is then transported through the blood to the lungs to be breathed out. Most of the CO2 in the blood exists in the form of bicarbonate, an electrolyte that is a main component of the body’s system for maintaining a stable acid-base (pH) balance.
This balance is managed by a chemical buffer system. When CO2 dissolves in blood, it combines with water to form carbonic acid. The lungs and kidneys are the primary organs that regulate this balance. The lungs control CO2 levels through the rate and depth of breathing; breathing faster expels more CO2, while breathing slower retains it. This respiratory control allows for rapid adjustments to pH.
Causes of Low Carbon Dioxide
The most frequent cause of low blood CO2 is hyperventilation. This over-breathing expels CO2 from the body too quickly, leading to a drop in blood levels. Hyperventilation is commonly triggered by psychological states such as anxiety, stress, or panic attacks as part of the body’s “fight or flight” response. Other physiological stressors like high fever, severe pain, or the body’s natural adjustment to high altitudes can also increase respiratory rate and induce hypocapnia.
Certain medical conditions can also lead to low CO2. Some lung diseases, like asthma or a pulmonary embolism (a blood clot in the lungs), can disrupt normal gas exchange and trigger rapid breathing. An overdose of certain medications, such as salicylates like aspirin, can directly stimulate the respiratory center in the brain, causing hyperventilation.
Low CO2 can also occur as a compensatory response to metabolic acidosis. In conditions like diabetic ketoacidosis or certain types of kidney disease, the body produces or retains too much acid. To counteract this, the respiratory system increases the breathing rate to blow off more CO2, which is acidic in the blood, in an attempt to raise the blood’s pH back toward a normal level.
Associated Symptoms and Diagnosis
The symptoms associated with low CO2 are primarily the result of the blood becoming too alkaline, a state known as respiratory alkalosis, and the constriction of blood vessels that supply the brain. This can lead to neurological symptoms such as dizziness, lightheadedness, and confusion. Many people also experience a tingling or numbness, known as paresthesia, particularly in the hands, feet, or around the mouth. Other possible symptoms include muscle cramps, spasms, and a feeling of shortness of breath.
Diagnosing the cause of low CO2 involves both laboratory tests and a thorough clinical evaluation. A routine blood test called a Basic Metabolic Panel (BMP) often includes a measurement of total CO2, which mainly reflects the bicarbonate level in venous blood. While this test can suggest an issue, a more definitive diagnostic tool is the Arterial Blood Gas (ABG) test. The ABG directly measures the partial pressure of CO2 (pCO2) and the pH in arterial blood, providing a clear picture of the respiratory component of acid-base balance.
Addressing and Managing Low Carbon Dioxide
The approach to managing low CO2 levels is centered on treating the specific underlying condition. When hyperventilation is triggered by anxiety or a panic attack, management focuses on calming the individual and restoring a normal breathing pattern. Techniques like pursed-lip or diaphragmatic (belly) breathing can help slow the respiratory rate, allowing CO2 to return to a normal level.
For medical causes, treatment is directed at the specific illness. In cases of diabetic ketoacidosis, this involves administering insulin and fluids to control blood sugar and correct the acidosis. If a lung condition or infection is the cause, treating that specific ailment will resolve the associated hyperventilation.
A known remedy for hyperventilation is breathing into a paper bag to rebreathe exhaled CO2 to help raise blood levels. However, this practice is not generally recommended without explicit medical guidance. If the cause of rapid breathing is a serious underlying issue like a heart attack or asthma, rebreathing CO2 could be unsafe and delay appropriate medical treatment.