PSV, now available in some infant ventilators ends inspiration when inspiratory flow falls below a set threshold. Insp. hold is eliminated and active exp. against a machine breath is avoided. Little is known about optimal breath termination criteria (BTC) or the effect of BTC on insp. time (IT) and tidal volume (TV) in neonates, especially if endotracheal tube leak (ETTL) is present. We varied BTC from 10%, 15%, 20% and 25% of peak flow and examined the effect on IT and TV with ETTL of 0, 10%, 20% using a small lung model with adjustable compliance and resistance, and a prototype Babylog vent. (Draeger Inc, Lubeck, Germ.). Data were analyzed by 2 way ANOVA for repeated measures. In the model of a 1kg infant with short time constants (TC) there was no significant relationship between BTC or leak on TV and IT. Data for a term infant model with longer TC is shown as mean ± SD. * p<0.01;⋄p<0.05 Table

Table 1
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The effect of ETTL up to 20% and BTC is negligible in small lungs with short TC. With longer TC the effect is statistically significant but clinically unimportant. The study was supported by Draeger Inc.