What is the rule for determining endotracheal (ET) tube depth in neonates?

From the Guidelines

The rule for determining the depth of endotracheal (ET) tube insertion in neonates is 6 + weight in kg. This formula provides an estimate of how many centimeters the tube should be inserted at the lip. For example, in a 3 kg neonate, the ET tube would be placed at approximately 9 cm at the lip (6 + 3 = 9). This rule helps ensure proper placement of the tube in the trachea, positioning it above the carina but below the vocal cords. Proper depth is critical in neonates because their airway anatomy is small, and even slight displacement can lead to either endobronchial intubation (if too deep) or accidental extubation (if too shallow). After placement using this rule, position should always be confirmed with chest rise, auscultation, and ideally a chest X-ray to verify the tube tip is at the appropriate level between the thoracic inlet and carina, as suggested by guidelines such as those from the American Heart Association 1.

Some key points to consider when placing an ET tube in a neonate include:

• Using the formula 6 + weight in kg to estimate the depth of insertion
• Confirming tube placement with clinical assessment such as chest movement and equal breath sounds bilaterally
• Using exhaled CO2 detection as a reliable method of confirmation of endotracheal tube placement, as noted in the 2015 American Heart Association guidelines update for cardiopulmonary resuscitation and emergency cardiovascular care 1
• Verifying the tube tip position with a chest X-ray to ensure it is at the appropriate level between the thoracic inlet and carina.

It is essential to prioritize proper ET tube placement in neonates to minimize complications and ensure the best possible outcomes in terms of morbidity, mortality, and quality of life.

From the Research

Rule of ET Tube Depth in Neonates

The rule of ET tube depth in neonates can be estimated using different formulas.

• One study 2 compared the performances of nasal septum-tragus length-based formula, body weight-based formula, and gestational age-based table in estimating the depth of oral endotracheal tube insertion in neonates.
• Another study 3 defined optimal initial ETT depth from the gum in infants relative to weight and compared the efficacy of point of care ultrasound with standard chest X-ray for confirming ETT tip position.
• The study found that the regression equation for optimal placement from the gum (in cm) was 5.21 + 1.03 × weight (kg).
• However, a different formula is mentioned in another study 4, which is weight + 6, and this formula was evaluated to determine its concordance with the ideal insertion depth of the endotracheal tube as evaluated by X-ray.
• The formula "weight in kilograms + 6 cm" for neonates weighing ≥ 1000 g is also mentioned in study 2.
• Other options such as "6 + age in weeks", "10 + age in months", and "3X ET tube size" are not supported by the provided studies as the primary method for estimating ET tube depth in neonates.
• Study 5 does mention the "3x ETT size" formula, but it is in the context of the pediatric population, not specifically neonates.
• Study 4 also mentions the "endotracheal tube × 3" formula, but again, it is in the context of children, not specifically neonates.