Relationship of neonatal endotracheal tube size and airway resistance

Abstract

Background: Infants receiving mechanical ventilation require narrow-lumen, small-diameter endotracheal tubes.

Objective: Compare the resistances of endotracheal tubes used in the neonatal intensive care unit.

Methods: Endotracheal tubes of internal diameter 2.5, 3.0, 3.5, and 4.0 mm were tested with a standard neonatal ventilator and a test lung. An endotracheal tube of each diameter was cut to 12 cm and connected to a flow transducer at one end and the test lung at the other. Serial measurements of resistance were made at various flows (6, 8, 10, and 12 L/min) and ventilator rates (30-90 breaths/min) encompassing the ranges of clinical practice. Analysis of variance was performed for each tube size, comparing resistance to flows and ventilator rates.

Results: Resistance was significantly higher with the 2.5 mm tube than with the others. There was also a consistent trend, in all the tube sizes, towards higher resistance as flow was increased.

Conclusions: The higher resistance of the 2.5 mm tube may be detrimental to extremely low birthweight infants kept on mechanical support merely "to grow." The higher resistance may increase the work of breathing and thus increase caloric expenditure and impede growth.