What is the recommended endotracheal tube (ETT) size for an adult woman?

Recommended Endotracheal Tube Size for Adult Women

For adult women, an endotracheal tube with an internal diameter of 7.0-7.5 mm is recommended, as suggested by the American Society of Anesthesiologists. 1

Evidence-Based Recommendations

The selection of appropriate endotracheal tube (ETT) size is crucial for ensuring adequate ventilation while minimizing airway trauma. Guidelines provide specific recommendations based on patient characteristics:

Standard ETT Sizing for Adult Women

• 7.0-7.5 mm internal diameter for adult women 1
• Fixation depth of 21 cm from the incisors for women 1

Important Considerations

Anatomical Factors

• Tracheal diameter in adults is highly variable and is narrowest at the subglottis 2
• Women tend to have smaller tracheal diameters than men, which must be considered during ETT selection 2

Risk of Oversizing

• 22% of patients are intubated with inappropriately large tubes (defined as 1.0 mm larger than recommended) 3
• Women are significantly more likely to be intubated with inappropriately large ETTs (OR = 13.58) 3
• Patients with height less than 160 cm are at particularly high risk (OR = 141) 3
• Oversized tubes can traumatize the airway and increase the risk of postoperative sore throat and hoarseness 2

Smaller Tube Considerations

• In difficult airway situations, a smaller tube (6.0-6.5 mm) can be considered to facilitate intubation 1
• Tracheal tubes as small as 6.0 mm will accommodate routinely used intubation aids, suction devices, and slim-line fibreoptic bronchoscopes 2
• Smaller tubes may reduce the risk of airway trauma without compromising ventilation 2

Special Circumstances

• For patients with status asthmaticus requiring mechanical ventilation, larger ETT sizes (≥7.5 mm) have been associated with lower mortality compared to smaller tubes (≤7.0 mm) 4

Verification of Proper Placement

After selecting the appropriate ETT size, proper placement should be verified through:

1. Clinical assessment (bilateral chest expansion and breath sounds)
2. Capnography (gold standard for confirmation)
3. 5-point check:
   • Inflating the cuff to 20-30 cmH₂O
   • Confirming placement with capnography
   • Securing the tube
   • Verifying bilateral chest expansion
   • Documenting tube depth 1

Common Pitfalls to Avoid

1. Generic selection based only on sex - Consider height and individual anatomy
2. Oversizing tubes in women - This is a common error that increases risk of airway trauma
3. Inadequate depth verification - The tip should be approximately 4-5 cm above the carina, with the cuff 1-2 cm below the vocal cords 1
4. Neglecting capnography - This is the gold standard for confirming proper placement

By following these evidence-based recommendations, clinicians can optimize ETT selection for adult women, balancing the need for adequate ventilation with minimizing the risk of airway trauma.