Background: Hypoxemic episodes in ventilated preterm infants are frequently caused by reduced ventilation due to a decrease in lung volume and acute worsening of respiratory mechanics.
Objective: To compare the efficacy of conventional time-cycled, pressure-limited flow synchronized intermittent mandatory ventilation (SIMV) and volume-targeted SIMV (VT-SIMV) in reducing the frequency and severity of these episodes.
Methods: SIMV and VT-SIMV were compared in preterm infants with frequent spontaneous episodes of hypoxemia. VT-SIMV was provided with the Draeger Babylog 8000plus ventilator in volume-guarantee mode.
Results: In all, 32 infants (birth weight 668 +/- 126 g, gestational age 24.8 +/- 1.1 weeks, age 37.5 +/- 17.3 days) were studied during 2-hour periods of SIMV and VT-SIMV in random sequence. In an initial phase, a group of 12 infants was supported during VT-SIMV with a target tidal volume of 4.5 ml/kg (VT-SIMV 4.5). A planned interim analysis did not show differences in frequency and duration of hypoxemia between VT-SIMV 4.5 and SIMV, and the initial phase was stopped. In a second phase of the study, 20 infants were studied while supported with a target tidal volume of 6.0 ml/kg during VT-SIMV (VT-SIMV 6.0). In the second phase of the study, the frequency of the hypoxemic episodes did not change but the mean episode duration was shorter during VT-SIMV compared to SIMV. The proportion of mechanical breaths with small tidal volumes (< or =3 ml/kg) was reduced during VT-SIMV 6.0 versus SIMV, while the peak inspiratory pressure and mean airway pressure were increased.
Conclusion: VT-SIMV did not reduce the frequency of hypoxemic episodes, but VT-SIMV 6.0 was effective in reducing the duration of the hypoxemic episodes.