Does chronic smoking cause decreased carbon dioxide (CO2) levels and an elevated anion gap?

From the Guidelines

Chronic smoking does not typically cause decreased carbon dioxide (CO2) levels or an elevated anion gap. In fact, chronic smokers often have normal or even slightly elevated CO2 levels due to chronic carbon dioxide retention, particularly if they develop chronic obstructive pulmonary disease (COPD) 1. Smoking itself does not directly affect the anion gap, which is a calculation used to assess acid-base balance in the blood. The anion gap may become elevated in certain conditions like diabetic ketoacidosis, lactic acidosis, or ingestion of certain toxins, but smoking is not a direct cause of these disturbances. While smoking introduces carbon monoxide into the bloodstream, which can reduce oxygen-carrying capacity, this does not typically alter CO2 levels or the anion gap in a clinically significant way. Some key points to consider include:

• The main risk exposure for COPD is tobacco smoking, but environmental exposures like biomass fuel exposure and air pollution may contribute 1.
• Smoking cessation is crucial in managing COPD and other cardiovascular diseases, with a reported 36% risk reduction of premature death in those who quit compared with those who continue to smoke 1.
• The use of electronic cigarettes (e-cigarettes) should be discouraged because they are not harm-free and can have adverse effects on the cardiovascular system 1.
• Carbon dioxide levels in the blood are controlled by chemical sensors, and increased levels of carbon dioxide will stimulate ventilation, thus increasing clearance from the lungs and therefore from the bloodstream 1.
• Smoking increases the risk of diabetes, cardiovascular diseases, and premature death, and should be avoided, including passive smoking 1. Overall, the most recent and highest quality study 1 suggests that chronic smoking does not directly cause decreased CO2 levels or an elevated anion gap, but rather may lead to secondary respiratory issues that could eventually cause acid-base disturbances.

From the Research

Chronic Smoking Effects on CO2 Levels and Anion Gap

• Chronic smoking is a major cause of chronic obstructive pulmonary disease (COPD) and can lead to respiratory acidosis, which is characterized by an increase in arterial partial pressure of carbon dioxide [(2,3,4)].
• However, the question asks about decreased CO2 levels, which is more commonly associated with respiratory alkalosis, a condition that can occur due to hyperventilation 4.
• There is no direct evidence in the provided studies to suggest that chronic smoking causes decreased CO2 levels [(2,3,4,5,6)].
• Regarding the anion gap, metabolic acidosis, which can be caused by various factors including lactic acidosis, can lead to an elevated anion gap 5.
• However, the relationship between chronic smoking and an elevated anion gap is not directly addressed in the provided studies [(2,3,4,5,6)].

Relationship Between Smoking and Acid-Base Disorders

• Smoking can contribute to the development of chronic obstructive pulmonary disease (COPD) and atherosclerotic cardiovascular disease (ASCVD), which can have complex and multifactorial effects on acid-base homeostasis 6.
• The components present in tobacco smoke can have adverse effects on various cellular functions, including macrophages and endothelial cells, which can lead to systemic inflammation and impaired endothelial function 6.
• However, the specific effects of chronic smoking on CO2 levels and anion gap are not clearly established in the provided studies [(2,3,4,5,6)].