Abstract 1846 Poster Session I, Saturday, 5/1 (poster 36)

Extremely low birthweight infants (ELBW) requiring mechanical ventilation are frequently treated with 2.5 mm diameter endotracheal tubes (ETT). This study was designed to measure the relative resistances of 2.5, 3.0, 3.5, and 4.0 mm ETT using a standard neonatal ventilator VIP BIRD infant/pediatric ventilator, Bird Products Corp., Palm Springs, CA) and a neonatal test lung (IngMar Medical, Pittsburgh, PA). Each ETT was cut to the same length and connected proximally to the flow transducer and distally to the test lung. For each tube, serial measurements of resistance (R) were made at varying gas flow rates (6-12 LPM) and ventilator rates (30, 60, and 90 bpm). All other ventilator parameters were held constant during the study. Analysis of variance (ANOVA) was performed for each tube size comparing flow rate and ventilatory rate to R. Neither flow rate nor respiratory rate had a statistically significant effect on R within a given tube size; therefore, all R measurements were aggregated for each tube size. Subsequent ANOVA demonstrated a statistically significant difference in measured R related to tube size between each tube size, p<0.001. The 2.5 mm ETT had a statistically significant increase in measured R compared to all other sized tubes using Dunnett's Post-Hoc analysis, p<0.001. (Table)

Table 1 No caption available
Full size table

There was also a trend for increasing R as flow rates were increased within each tube size In this lung model, the use of the 2.5 mm ETT was associated with more than a 25% increase in R. This increase in R may be detrimental to the mechanically-ventilated ELBW who is left on the ventilator "to grow." Instead of enhancing growth, it may increase the work of breathing, result in a greater caloric expenditure, and actually impede growth.