From the Guidelines
Low CO2 levels on a chemistry panel are most commonly caused by hyperventilation, which can be triggered by various factors such as anxiety, panic attacks, or high altitude exposure, as the body's physiological response to eliminate excess carbon dioxide is highly sensitive to changes in respiratory rate and depth 1.
Causes of Low CO2 Levels
Some of the key causes of low CO2 levels include:
- Hyperventilation, which can be caused by anxiety, panic attacks, pain, or high altitude exposure
- Metabolic acidosis, where the body compensates by increasing breathing rate to eliminate acids
- Severe infections, such as sepsis, which can lead to increased respiratory rate
- Liver disease, which can affect the body's ability to regulate acid-base balance
- Diabetic ketoacidosis, a condition characterized by high blood sugar and acidosis
- Salicylate toxicity, or aspirin overdose, which can stimulate the respiratory center and increase breathing rate
- Certain medications, such as diuretics or metformin, which can affect acid-base balance
- Pulmonary conditions, like asthma or pneumonia, which can alter breathing patterns
- Hormonal imbalances, such as hyperthyroidism, which can increase metabolic rate and respiratory drive
Physiological Basis
According to the BTS guideline for oxygen use in adults in healthcare and emergency settings 1, carbon dioxide is a product of the body's metabolism and is cleared from the body through the lungs and kidneys. The normal range for carbon dioxide levels in the blood is 4.6–6.1 kPa or 34–46 mm Hg, and increased levels of carbon dioxide will stimulate ventilation to increase clearance from the lungs and bloodstream.
Clinical Implications
It is essential to identify and address the underlying cause of low CO2 levels, as treatment will depend on the specific cause. In some cases, managing anxiety or treating infections may be sufficient, while in other cases, adjusting medications or correcting metabolic abnormalities may be necessary. In severe cases, breathing into a paper bag may temporarily help by allowing rebreathing of exhaled CO2, but this should only be done under medical supervision.
From the Research
Causes of Low CO2 in Chemistry
- Metabolic acidosis can cause low CO2 levels in the blood, which can be categorized into two types: high-anion-gap metabolic acidosis and hyperchloremic (or normal anion gap) metabolic acidosis 2
- High-anion-gap metabolic acidosis can be caused by the accumulation of endogenous acids that consume bicarbonate, such as lactic acidosis, ketoacidosis, renal failure, and intoxication with certain substances like ethylene glycol, methanol, and salicylate 2
- Hyperchloremic metabolic acidosis can occur due to the loss of bicarbonate from the gastrointestinal tract or the kidney, and can be caused by factors such as gastrointestinal bicarbonate loss, renal tubular acidosis, and administration of acids 2
- In some cases, low CO2 levels can be caused by laboratory errors, such as interference with the enzymatic assay used to measure total carbon dioxide levels 3
- It is essential to identify the primary causative etiology of metabolic acidosis as quickly as possible, and to categorize the metabolic acidosis as hyperchloremic or high-anion-gap type to guide further diagnostic studies 4
Laboratory Errors
- Laboratory errors can cause discrepancies between total carbon dioxide levels measured using an enzymatic assay and gas panel-derived plasma bicarbonate levels 3
- Endogenous interferents, such as paraproteins or endogenous antibodies, can cause turbidity in the enzymatic assay, resulting in falsely low total carbon dioxide values 3
Clinical Implications
- Metabolic acidosis can have serious clinical implications, and prompt identification and treatment of the underlying cause are crucial to prevent morbidity and mortality 5, 6, 2
- The treatment of metabolic acidosis depends on the underlying cause, and may involve cessation of acid production, improvement of tissue oxygenation, and correction of electrolyte imbalances 6, 2