Double-Lumen Tube Size 39 French: Inner Diameter Equivalence
A 39 French double-lumen tube does not have a direct single-lumen endotracheal tube equivalent with the same inner diameter, as double-lumen tubes have two smaller lumens rather than one large lumen—the bronchial and tracheal lumens of a 39F DLT each have significantly smaller internal diameters than standard single-lumen tubes.
Understanding the Dimensional Differences
The question reflects a common misconception about double-lumen tube sizing. The French size (39F) refers to the outer diameter of the entire double-lumen tube assembly, not the inner diameter of either individual lumen 1.
Key Dimensional Facts:
- 39F DLT outer diameter: Approximately 13 mm (39 French ÷ 3 = 13 mm) 1
- Individual lumen diameters: Each of the two lumens (bronchial and tracheal) within a 39F DLT has a much smaller internal diameter than a single-lumen tube of equivalent outer size 2
- Functional limitation: Double-lumen tubes have smaller lumens that do not permit therapeutic bronchoscopes to pass through easily, unlike larger single-lumen tubes 2
Clinical Implications for Tube Selection
When Single-Lumen Tubes Are Preferred:
In massive hemoptysis, a single-lumen cuffed endotracheal tube with a larger diameter is generally more beneficial than a double-lumen tube because it allows bronchoscopic suctioning and removal of large obstructing clots quickly 2.
Standard DLT Sizing Recommendations:
- Males: 37F is the standard recommended size 3, 4
- Females: 35F is the standard recommended size 3, 4
- 39F DLTs: Reserved for larger patients, typically males with left main bronchus diameter >12 mm 5
- Sizes 0.5 mm smaller and larger should be immediately available for adjustment 3
Common Pitfall to Avoid
Do not assume French size correlates with functional inner diameter equivalence between double-lumen and single-lumen tubes. The French sizing system measures outer circumference, and the dual-lumen design of DLTs means each individual lumen has substantially reduced cross-sectional area compared to a single-lumen tube 1. This is why double-lumen tubes are too bulky for prolonged ventilation and require exchange to single-lumen tubes postoperatively when continued mechanical ventilation is needed 3, 6.
Practical Consideration:
If you need to exchange a 39F DLT for a single-lumen tube postoperatively, select the single-lumen tube size based on standard airway assessment criteria (typically 7.5-8.5 mm ID for adults), not by attempting to match the DLT's French size 6.