What are the causes of a carbon dioxide (CO2) level of 35, also known as hypocapnia?

From the Guidelines

A CO2 level of 35 is most likely caused by hyperventilation, which can be due to anxiety, pain, or other stressors, leading to excessive breathing out of CO2, as stated in the BTS guideline for oxygen use in adults in healthcare and emergency settings 1. The most common causes of a CO2 level of 35 include:

• Hyperventilation, which can be due to anxiety, pain, or other stressors, leading to excessive breathing out of CO2
• Metabolic acidosis, where the body produces too much acid or cannot remove it effectively, can also lower CO2 levels, as seen in conditions like diabetic ketoacidosis, severe diarrhea, or kidney disease 1
• Certain medications, particularly diuretics or some types of antibiotics, can contribute to low CO2 levels
• High altitude exposure can also decrease CO2 due to the body's adaptation to lower oxygen levels
• Lung diseases that affect gas exchange, such as emphysema or severe asthma, can also cause low CO2 levels To address this, it's essential to identify and treat the underlying cause. For anxiety-related hyperventilation, breathing exercises and relaxation techniques can help, as suggested by the BTS guideline 1. For metabolic causes, addressing the primary condition (e.g., managing diabetes, treating infections) is crucial, as stated in the guideline for oxygen use in adults in healthcare and emergency settings 1. If medication-related, adjusting dosages under medical supervision may be necessary. In all cases, a thorough medical evaluation is recommended to determine the exact cause and appropriate treatment. Key points to consider:
• The normal range for CO2 levels is 4.6–6.1 kPa or 34–46 mm Hg, as stated in the BTS guideline for oxygen use in adults in healthcare and emergency settings 1
• Hyperventilation can lead to respiratory alkalosis, which can cause symptoms such as dizziness, lightheadedness, and tingling in the hands and feet
• Metabolic acidosis can cause symptoms such as nausea, vomiting, and abdominal pain
• A thorough medical evaluation is necessary to determine the underlying cause of a CO2 level of 35 and to develop an appropriate treatment plan.

From the Research

Causes of Hypocapnia

• Hypocapnia, a state of reduced carbon dioxide (CO2) level in the blood, can be caused by various factors, including high-intensity exercise 2
• During high-intensity exercise, the body's CO2 level can drop, leading to hypocapnia, which can become more noticeable during recovery or between seasons of intermittent exercise 2
• Other potential causes of hypocapnia include respiratory disorders, such as chronic obstructive pulmonary disease (COPD), and cardiac conditions, such as congestive heart failure (CHF) 3
• Neuromuscular disorders can also lead to hypocapnia, particularly in patients with respiratory failure 4

CO2 Levels and Hypocapnia

• A CO2 level of 35 mmHg is considered low and can indicate hypocapnia 4
• Normal CO2 levels typically range from 35-47 mmHg, and levels below this range can indicate hypocapnia 4
• Hypocapnia can be diagnosed using various methods, including end-tidal CO2 measurement and transcutaneous CO2 monitoring 3, 4

Exercise and Hypocapnia

• High-intensity exercise can lead to hypocapnia due to increased ventilation and CO2 removal from the body 2
• Hypercapnic breathing after exercise may not be an effective strategy to reverse exercise-induced hypocapnia, as it can lead to increased CO2 removal from the body and decreased O2 supply to the muscles 2