How do you determine the size and depth of cuffed endotracheal tube (ETT) versus uncuffed ETT?

Determining Endotracheal Tube Size and Depth for Cuffed vs. Uncuffed ETTs

For pediatric patients, cuffed endotracheal tubes are preferred over uncuffed tubes in most circumstances, with specific size formulas based on age and weight. 1

Cuffed Endotracheal Tube Size Selection

For Infants and Young Children

• For infants ≥3.5 kg and <1 year of age: Use a 3.0 mm ID cuffed ETT 1, 2
• For children between 1-2 years of age: Use a 3.5 mm ID cuffed ETT 1

For Children >2 Years of Age

• Use the formula: ID (mm) = (age in years/4) + 3.5 1
• If resistance is met during insertion, use a tube with ID 0.5 mm smaller 1
• If no leak is present with cuff deflated, consider reintubation with a tube 0.5 mm smaller when patient is stable 1

Uncuffed Endotracheal Tube Size Selection

• For infants <1 year: Use a 3.5 mm ID uncuffed ETT 2
• For children >1 year: Use the formula: ID (mm) = (age in years/4) + 4 1
• Uncuffed tubes are generally 0.5-1.0 mm larger in internal diameter than their cuffed counterparts for the same age patient 3

Depth of Insertion

• For infants and children: Depth of insertion (cm at lip) = weight in kg + 6 cm 2
• Alternative method: Depth (cm) = 3 × internal diameter of the tube 2
• For oral intubation in children >2 years: Depth (cm) = (age/2) + 12 1

Advantages of Cuffed ETTs

• Cuffed tubes are preferred in circumstances such as poor lung compliance, high airway resistance, or large glottic air leak 1, 2
• Cuffed tubes reduce the risk of aspiration 2
• Cuffed tubes decrease the need for tube changes due to inappropriate size selection 3
• When using cuffed tubes, monitor cuff inflation pressure and maintain below 20-25 cm H₂O to prevent tracheal damage 2, 3

Practical Considerations

• Always have tubes 0.5 mm smaller and 0.5 mm larger than the estimated size available 2
• Length-based resuscitation tapes may be more accurate than age-based formulas for determining tube size in children up to 35 kg 2
• Using a tube that is too small requires higher cuff pressures to seal the airway, transforming a high-volume, low-pressure cuff into a high-volume, high-pressure cuff, increasing risk of tracheal damage 3
• Ultrasonographic measurement of subglottic diameter can be used to predict appropriate cuffed ETT size with approximately 86% first-attempt success 4

Verification of Proper Placement

• Verify proper tube placement using multiple methods 2:
  • Look for bilateral chest movement
  • Listen for equal breath sounds over both lung fields
  • Check for absence of gastric insufflation sounds
  • Use end-tidal CO₂ detection capability 1
  • If available, use continuous waveform capnography as the most reliable method 1

Common Pitfalls and Considerations

• Remember the "DOPE" mnemonic if deterioration occurs after intubation: Displacement, Obstruction, Pneumothorax, Equipment failure 2
• Maintain the patient's head in neutral position after securing the tube; flexion may advance the tube further, while extension may withdraw it 2
• Some studies suggest that the Khine formula (ID = age/4 + 3) may underestimate optimal cuffed tube size by 0.5 mm 5
• If using the traditional Khine formula, be prepared to potentially upsize by 0.5 mm if there is excessive leak around the tube 5

By following these guidelines, you can select the appropriate size and depth for both cuffed and uncuffed endotracheal tubes in pediatric patients, optimizing ventilation while minimizing the risk of complications.