Pediatric Endotracheal Tube Size and Fixing Length
Tube Size Selection
For cuffed endotracheal tubes in children over 2 years of age, use the formula: Internal Diameter (mm) = (age in years/4) + 3.5, which provides the most reliable estimation based on current American Heart Association and International Consensus guidelines. 1, 2
Age-Specific Cuffed Tube Sizing
Infants ≥3.5 kg to <1 year: Use a 3.0 mm internal diameter (ID) cuffed tube 1, 2
Children >2 years: Apply the formula ID (mm) = (age/4) + 3.5 1, 2
Uncuffed Tube Sizing (When Used)
Children >1 year: Use the formula ID (mm) = (age/4) + 4 2
The traditional formula (age + 16)/4 has demonstrated acceptable reliability in clinical practice 3
Cuffed vs Uncuffed Tubes
Both cuffed and uncuffed endotracheal tubes are acceptable for intubating infants and children, though cuffed tubes are increasingly preferred. 1
Cuffed tubes are preferable in circumstances of poor lung compliance, high airway resistance, or large glottic air leak 1, 2
Cuffed tubes reduce aspiration risk compared to uncuffed tubes 1, 2
When using cuffed tubes, avoid excessive cuff pressures to prevent tracheal injury 1
Depth of Insertion (Fixing Length)
The depth of endotracheal tube insertion at the lip can be calculated using: depth (cm) = weight (kg) + 6 cm. 2
Alternative Depth Formulas
Three times the internal diameter: Depth (cm) = 3 × ID of the tube 2
For oral intubation in children >2 years: Depth (cm) = (age/2) + 12 2
Critical Adjustments During Insertion
If the tracheal tube meets resistance during insertion, immediately use a tube with ID 0.5 mm smaller. 1
If there is no audible leak around the tube with the cuff deflated after successful intubation, consider reintubation with a tube ID 0.5 mm smaller when the patient is stable. 1
Verification of Proper Placement
Confirm placement using multiple methods: bilateral chest movement, equal breath sounds, absence of gastric insufflation sounds 2
Continuous waveform capnography is the most reliable method for verifying proper tube placement 2
For children >20 kg with a perfusing rhythm, an esophageal detector device may be considered if capnography is unavailable 1
Common Pitfalls and Practical Considerations
The older formula (age + 18)/4 has a high failure rate (89% incorrect) and should not be used 3
Age-based formulas alone have reported inaccuracy rates up to 60% 4
Always have tubes 0.5 mm smaller and larger readily available at the bedside, as formulas provide estimates rather than guarantees 5
For malnourished children (weight <3rd percentile), standard formulas may overestimate tube size; consider weight-based adjustments 4
Ultrasonographic measurement of subglottic diameter achieves 96-98% accuracy in predicting optimal tube size, superior to age-based formulas, when expertise and equipment are available 6
In pediatric cardiac patients with congenital heart disease, Cole's formula tends to underestimate required tube size by 0.5 mm or more in 29% of cases 7