Factors affecting ¹³C-natural abundance measurement of breath carbon dioxide during surgery: Absorption of carbon dioxide during endoscopic procedures

The aim of this paper is to review the factors which may affect breath ¹³CO₂/¹²CO₂ natural abundance in patients undergoing surgery or intensive care. Intravenous glucose administration is a major determinant of the ¹³CO₂/ ¹²CO₂ of breath as intravenous glucose preparations are almost all derived from cornstarch. In addition, the oxidation of endogenous substrates can affect the ¹³CO₂/¹²CO ₂ ratio. During many endoscopic procedures, such as laparoscopic surgery, carbon dioxide insufflation is used to provide a working space. As medical CO₂ is relatively depleted in ¹³CO₂ compared with endogenous and exogenous metabolic CO₂ sources, breath ¹³CO₂/¹²CO₂ measurements can be used to estimate CO₂ absorption during these procedures. However, all these factors may also be affected by the bicarbonate pool, making a definitive attribution of changes in breath ¹³CO₂/ ¹²CO₂ to a single factor problematic.