Validity of Three Formulas for Measuring Endotracheal Tube Insertion Depth in Children under Mechanical Ventilation

Background: In the process of intubation, inappropriate placement of the endotracheal tube can lead to hypoxemia, aspiration, insufficient ventilation, atelectasis, barotrauma and pneumothorax. The above complications may be difficult for a patient with severe disease to tolerate; especially when inappropriate placement is not detected by the specialist in the initial evaluation and the diagnosis lasts until the confirmatory chest x-ray is performed. This study evaluated the validity of three formulas in measuring the depth of endotracheal intubation in children under mechanical ventilation. Methods: ۶۰ intubated children aged ۲ months to ۱۲ years were included in this study. The patients were randomly divided into three study groups. Endotracheal tube length for each patient was calculated on the basis of the endotracheal tube length formulas (۱۲ + age (years) / ۲; endotracheal tube diameter * ۳; and ۵ + height (cm) / ۱۰). The ideal depth of the endotracheal tube based on chest x-ray was measured as the median distance between the first thoracic vertebra (T۱) and the carina in cm. The distance between the ideal depth of the endotracheal tube and the end location of the endotracheal tube was also measured and recorded. Results: The mean age of the patients was ۴۲.۹۰ months and ۵۸.۳% of them were boys. The most common indication for intubation was pneumonia, along with respiratory distress (۳۳.۳%). Considering the difference in endotracheal tube depth between the two values calculated using the formula and chest X-ray equal to± ۰.۵ cm, formula ۱۲ + (۲ / age) in ۵۵% of patients, formula ۳ * endotracheal tube length in ۷۰% patients and formula ۵ + (۱۰ / height) in ۸۵% of patients, were correctly estimated endotracheal tube length. On the other hand, it was observed that in ۱۵%, ۴۵% and ۴۰% of the patients, the formula predicted the correct length of the endotracheal tube for correct intubation without any difference while compared to the chest X-ray. In evaluating the results obtained from the formula and length of the endotracheal tube measured by chest X-ray, it was also observed that the formulas ۱۲ + (۲ / age), ۳ * length of the endotracheal tube and ۵ + (۱۰ / height) were significantly correlated with CXR. Conclusion: According to the obtained results, it can be concluded that the formulas used to estimate the depth of endotracheal tube placement in children have low accuracies compared to the gold standard of measurement (chest X-ray). Of course, in comparison to the three formulas (height, weight and diameter of the ETT), the height formula was more accurate than others.