Adult Critical Care Specialty (ACCS) Practice Exam

A patient has been intubated and has an end tidal CO2 reading of 4%. What should the specialist suspect?

1. Patient has a pulmonary embolus

2. ET tube is in the correct position

3. ET tube is in the esophagus

4. ET tube is in the right main stem bronchus

The correct answer is: ET tube is in the correct position

An end-tidal CO2 reading of 4% indicates that the patient is effectively ventilating and that the exhaled carbon dioxide is being monitored accurately. In a normal range, end-tidal CO2 values typically fall between 35% to 45%, but if a reading of 4% is recorded shortly after intubation and it is consistent, it suggests that the tube may not be correctly placed in the trachea. In cases where the end-tidal CO2 reading is significantly lower than expected, one must suspect that the endotracheal tube may be in the esophagus. A value close to 4% could lead to consideration of an esophageal placement since CO2 is primarily produced in the lungs, and the esophagus would not produce effective amounts of CO2 to register a substantial reading. In contrast, if the ET tube were in the correct position, one would anticipate a much higher reading due to normal lung function and adequate ventilation. Key differential diagnoses would arise from extremely low readings indicating potential misplacement or inadequate ventilation. Thus, based on the provided information, while the correct answer suggests that the ET tube is in the right position, indicating effective ventilation, which would correlate with a higher end-tidal CO2