How is pediatric endotracheal tube (ETT) size calculated?

Pediatric Endotracheal Tube Size Calculation

Primary Recommendation

Use length-based resuscitation tapes for children up to 35 kg when available, as they are more accurate than age-based formulas; when tapes are unavailable, apply age-based formulas with cuffed tubes preferred over uncuffed tubes in most circumstances. 1, 2

Age-Based Formulas

For Cuffed Endotracheal Tubes (Preferred)

• Infants <1 year of age: Use a 3.0 mm internal diameter (ID) tube 1, 2, 3
• Children 1-2 years of age: Use a 3.5 mm ID tube 1, 2, 3
• Children >2 years of age: Use the formula ID (mm) = (age in years ÷ 4) + 3.5 1, 2, 3

For Uncuffed Endotracheal Tubes

• Infants up to 1 year: Use a 3.5 mm ID tube 1, 2
• Children 1-2 years: Use a 4.0 mm ID tube 1
• Children >2 years: Use the formula ID (mm) = (age in years ÷ 4) + 4 1, 3

Depth of Insertion

Calculate the depth of insertion using one of these methods:

• Primary formula: Depth at lip (cm) = weight in kg + 6 cm 2, 3
• Alternative formula: Depth (cm) = 3 × internal diameter of the tube 2, 3
• For children >2 years (oral intubation): Depth (cm) = (age ÷ 2) + 12 3

Clinical Advantages of Cuffed Tubes

Cuffed endotracheal tubes are preferable in specific clinical scenarios (Class IIa, LOE B) including: 1, 2, 4

• Poor lung compliance 1, 2, 4
• High airway resistance 1, 2, 4
• Large glottic air leak 1, 2, 4
• Risk of aspiration 2, 4

When using cuffed tubes, monitor cuff inflation pressure and maintain it below 20-25 cm H₂O per manufacturer instructions. 2, 4

Essential Preparation Steps

Always have tubes 0.5 mm smaller AND 0.5 mm larger than your calculated size immediately available before intubation. 1, 2, 4

• If the tube meets resistance during insertion, immediately use a tube 0.5 mm smaller 1, 2, 4
• If a large glottic air leak interferes with oxygenation/ventilation after placement, consider replacing with a tube 0.5 mm larger or switching to a cuffed tube of the same size 1, 2, 4

Verification of Proper Placement (Class I, LOE B)

Use multiple confirmation methods immediately after intubation: 1, 2

• Visualize bilateral chest movement 1, 2
• Auscultate for equal breath sounds over both lung fields, especially the axillae 1, 2
• Confirm absence of gastric insufflation sounds over the stomach 1, 2
• Check for exhaled CO₂ using capnography or colorimetry 1, 2
• Monitor oxyhemoglobin saturation with pulse oximetry if perfusing rhythm present 1, 2
• Perform chest x-ray in hospital settings to verify midtracheal position 1, 2
• Direct laryngoscopy if uncertain—visualize tube between vocal cords 1, 2

Critical Pitfalls and Troubleshooting

If an intubated patient's condition deteriorates, use the DOPE mnemonic: 1, 2

• Displacement of the tube
• Obstruction of the tube
• Pneumothorax
• Equipment failure

Maintain the patient's head in neutral position after securing the tube—neck flexion pushes the tube deeper into the airway, while extension may pull it out. 1, 2

Tube replacement carries significant risks and should only be performed in an appropriate setting by experienced personnel. 1, 4

Alternative Methods

While ultrasound measurement of subglottic diameter shows promise for predicting appropriate ETT size with strong correlation (R² = 0.834), this technique requires specialized equipment and training, making age-based formulas more practical for emergency situations. 5, 6 Traditional methods using finger width or diameter are inaccurate and should be avoided. 7