From the Guidelines
Low carbon dioxide levels, or hypocapnia, are primarily caused by hyperventilation, which can occur due to various reasons such as anxiety attacks, physiological hyperventilation, or pathological conditions like COPD exacerbations, as stated in the BTS guideline for oxygen use in adults in healthcare and emergency settings 1.
Causes of Hypocapnia
- Hyperventilation during anxiety attacks or physiological hyperventilation can lead to hypocapnia, as the body exhales more carbon dioxide than it produces, resulting in lower levels of carbon dioxide in the blood.
- Pathological hypoventilation, on the other hand, may not directly cause hypocapnia but can lead to hypercapnia; however, the reverse process of hyperventilation can cause hypocapnia, as seen in patients with COPD who may experience hyperventilation during exacerbations.
- Other causes of hypocapnia may include metabolic disorders, certain medications, high altitudes, and severe liver disease, although these are not directly mentioned in the provided study 1.
Clinical Implications
- It is essential to identify and address the underlying cause of hypocapnia, as persistent abnormal levels of carbon dioxide can lead to acid-base imbalance in the body.
- Treatment may involve breathing techniques for anxiety-related hyperventilation, medication adjustments, or treating underlying metabolic disorders, as appropriate.
- The BTS guideline for oxygen use in adults in healthcare and emergency settings 1 provides valuable insights into the physiological principles underlying hypoventilation and hyperventilation, which can help guide clinical decision-making in patients with hypocapnia.
From the Research
Possible Reasons for Low Carbon Dioxide Levels
- Hyperventilation: According to 2, hyperventilation can lead to low carbon dioxide levels (hypocapnia) in the blood, which may be a physiological response to hypercapnia.
- Panic Disorder: Studies such as 3 and 4 suggest that patients with panic disorder may be biologically hypersensitive to CO2 inhalation and may hyperventilate to keep pCO2 low, which can lead to low carbon dioxide levels.
- Metabolic Alkalosis: As mentioned in 5, metabolic alkalosis can coexist with respiratory failure, and treatment with acetazolamide can help improve oxygenation by reducing metabolic alkalosis and increasing CO2 levels.
- Chronic Hyperventilation: Chronic hyperventilation, as discussed in 4, can lead to cerebral hypoxia, which may contribute to the chronicity of panic and anxiety symptoms, and may be a self-perpetuating mechanism in the pathophysiology of panic disorder.
- Respiratory Stimulation: The use of acetazolamide, as shown in 3, may not stimulate ventilation, even if it affects CO2 levels, which could lead to low carbon dioxide levels if the body's response to increased CO2 is impaired.