What is the recommended depth of insertion for an endotracheal tube (ET tube) in neonates?

Recommended Depth of Insertion for Endotracheal Tubes in Neonates

For neonates, the recommended depth of insertion for an endotracheal tube at the lip is weight in kg + 6 cm, which provides appropriate positioning in the midtrachea in most cases. 1

Endotracheal Tube Size Selection

• For emergency intubation of infants less than 1 year of age:
  • If using a cuffed tube: select a 3.0 mm ID tube 1, 2
  • If using an uncuffed tube: select a 3.5 mm ID tube 1, 2
• Both cuffed and uncuffed endotracheal tubes are acceptable for intubating neonates (Class IIa, LOE C) 1, 2
• Cuffed tubes may be preferable in certain circumstances such as poor lung compliance, high airway resistance, or large glottic air leak (Class IIa, LOE B) 1, 2

Depth of Insertion Formulas

• Primary recommendation: Depth of insertion (cm at lip) = weight in kg + 6 cm 1, 3
• Alternative method: Depth can be estimated as 3 times the internal diameter of the tube 1
• For extremely low birth weight infants (<750g), the weight-based formula may need adjustment as it tends to overestimate the proper depth 4

Verification of Proper Tube Placement

• Verify proper tube placement using multiple methods immediately after intubation (Class I, LOE B) 2, 1:
  • Look for bilateral chest movement 2
  • Listen for equal breath sounds over both lung fields, especially over the axillae 2
  • Listen for absence of gastric insufflation sounds over the stomach 2
  • Check for exhaled CO2 (capnography or colorimetry) 2
  • If perfusing rhythm is present, monitor oxyhemoglobin saturation with pulse oximetry 2
  • In hospital settings, perform a chest x-ray to verify proper position in the midtrachea 2

Research on Alternative Methods

• Studies comparing nasal-tragus length (NTL) + 1 cm formula with the weight-based formula have shown mixed results:
  • One study found NTL + 1 cm to be a better predictor in term Indian neonates 5
  • Another study found no significant difference between using the vocal cord guide versus the weight-based formula 6
  • For extremely low birth weight infants (<750g), the standard weight-based formula often results in ETT placement that is too deep 4

Common Pitfalls and Considerations

• Remember the "DOPE" mnemonic if a patient's condition deteriorates after intubation: Displacement, Obstruction, Pneumothorax, Equipment failure 2
• Maintain the patient's head in neutral position after securing the tube; neck flexion may push the tube further into the airway, while extension may pull it out 2
• Have tubes 0.5 mm smaller and 0.5 mm larger than the estimated size available during intubation 2
• If resistance is met during intubation, use a tube 0.5 mm smaller 2
• If a large glottic air leak interferes with oxygenation or ventilation after intubation with an uncuffed tube, consider replacing with a tube 0.5 mm larger or switching to a cuffed tube of the same size 2
• Tube replacement carries risks and should be performed in an appropriate setting by experienced personnel 2
• For premature infants <1 kg, the accuracy of current formulas is poor, with one study showing only 47% accuracy using a weight-based formula, highlighting the need for rapid radiologic assessment in this population 7

Optimal Positioning

• The optimal position for an ETT tip is between the upper border of the first thoracic vertebra (T1) and the lower border of the second thoracic vertebra (T2) 6
• Most incorrectly positioned ETTs (87% in one study) are placed too low rather than too high 6
• For extremely low birth weight infants (<750g), the standard formula often results in ETT placement that is too deep 4