We evaluated the resistance to gas flow in vitro in regular and trimmed endotracheal tubes of different size and in several commercially available nasal CPAP devices of different size. The highest resistance—141 cm H 2 O/L/s at 6 L/min flowrate and 92 cm H 2 O/L/s at 3 L/min—was present in the longest nasal device (6.0 cm) with the smallest diameter (ID, 1.7 mm; OD, 2.5 mm). Of the shorter nasal devices (0.5-1.0 cm), the one with the largest diameter (ID, 3.0 mm; OD, 5.5 mm) had the lowest resistance—11 cm H 2 O/L/s at 6 L/min flowrate and 8 cm H 2 O/L/s at 3 L/min. The resistance present in most devices was similar to the natural resistance in the upper airway and, therefore, should have minimal impact on the work of breathing.
Czervinske et al. (Wed,) studied this question.
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