Endotracheal Tube Size and Intubation Equipment for a 3-Month-Old Baby
For a 3-month-old baby, use a 3.0 mm ID cuffed endotracheal tube or a 3.5 mm ID uncuffed tube, inserted to a depth of weight in kg + 6 cm at the lip, with a straight Miller size 1 laryngoscope blade, and a size 0 oropharyngeal airway (pink color). 1
Endotracheal Tube Selection
- For a 3-month-old infant, both cuffed and uncuffed endotracheal tubes are acceptable options (Class IIa, LOE C) 2, 1
- If using a cuffed tube, select a 3.0 mm internal diameter (ID) tube 1, 3
- If using an uncuffed tube, select a 3.5 mm ID tube 1, 3
- Always have tubes 0.5 mm smaller and 0.5 mm larger than the estimated size available during intubation 1, 4
Depth of Insertion
- Calculate depth of insertion (cm at lip) = weight in kg + 6 cm 1
- Alternatively, depth can be estimated as 3 times the internal diameter of the tube 1
- For example, for a 6 kg infant: 6 + 6 = 12 cm at the lip 1
Laryngoscope Blade
- For a 3-month-old infant, a straight Miller size 1 blade is recommended 1
- Straight blades are generally preferred for infants under 1 year as they provide better visualization by directly lifting the epiglottis 1
Oropharyngeal Airway
- For a 3-month-old infant, use a size 0 oropharyngeal airway 2
- Oropharyngeal airways are typically color-coded, with size 0 being pink 2
Verification of Tube Placement
- Verify proper tube placement using multiple methods (Class I, LOE B) 1:
- Look for bilateral chest movement
- Listen for equal breath sounds over both lung fields, especially over the axillae
- Listen for absence of gastric insufflation sounds
- Check for exhaled CO2 (end-tidal CO2 monitoring is optimal for confirming tube placement) 2
- If perfusing rhythm is present, monitor oxygen saturation with pulse oximetry
Important Considerations
- 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) 2, 3
- If using a cuffed tube, monitor cuff inflation pressure and keep it below 20-25 cm H2O to prevent tracheal mucosal damage 1, 3
- Age-based formulas are not always accurate for predicting the appropriate ETT size 5, 6
- Length-based resuscitation tapes provide more accurate tube size estimates than age-based formulas 1, 3
Common Pitfalls to Avoid
- Remember the "DOPE" mnemonic if the patient's condition deteriorates after intubation: Displacement, Obstruction, Pneumothorax, Equipment failure 1
- 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 1
- Avoid excessive ventilation during resuscitation (Class III, LOE C) 2
- Do not continue cricoid pressure if it interferes with ventilation or the speed/ease of intubation (Class III, LOE C) 2