Reliability of capnography in identifying esophageal intubation with carbonated beverage or antacid in the stomach

To evaluate the reliability of capnography in identifying esophageal intubation in the presence of a carbonated beverage in the stomach, we first investigated the amount of CO₂ released from different carbonated beverages and antacids in a simulated stomach; next we measured the end-expired CO₂ level during esophageal ventilation with a carbonated beverage in the stomachs of six swine. CO₂ levels of approximately 20% were consistently observed in all carbonated beverages. The CO₂ levels obtained with sodium bicarbonate, Maalox, and sodium citrate were 19.3%, 2.0%, and 0%, respectively. CO₂ waveforms were observed during esophageal ventilation in five of six animals after intragastric administration of a carbonated beverage. An end-expired CO₂ level of 2.5% or more was observed in two swine. The highest end-expired CO₂, level measured was 5.3%. We conclude that although capnography is convenient and effective, it lacks all the attributes of an ideal monitor for detecting esophageal intubation.