Neonatal volume guarantee ventilation: effects of spontaneous breathing, triggered and untriggered inflations

Background: During volume guarantee (VG) ventilation the peak inflating pressure (PIP) for each ventilator inflation is adjusted to ensure the expired tidal volume (VTe) is close to the set VTe. Differences in the PIP between inflations triggered by the infant's inspirations and untriggered inflations are seen. Aim: To investigate the effects of triggered and untriggered inflations on PIP and VTe. Methods: Neonates were ventilated with the Dräger Babylog 8000 using assist control (synchronous intermittent positive pressure ventilation) and VG modes. Continuous recordings of ventilator pressures and tidal volumes were made at 200 Hz for 10 minutes. Results: In 10 infants, 6540 inflations were analysed, of which 4052 (62%) were triggered. Triggered inflations had a significantly lower mean (SD) PIP than untriggered inflations: 12.9 (4.9) vs 17.0 (3.3) cm H2O, (p<0.001). Despite this, there was no significant difference in the V Te of each type of inflation (103% and 101% of the set V Te, respectively). When a triggered inflation was immediately preceded or followed by an untriggered inflation the PIP changed by about 5 cm H2O. Between adjacent inflations of the same type, the change in PIP was less than 3 cm H2O: for triggered inflations it was 0.11 (1.50) cm H2O and for untriggered inflations 0.06 (1.53) cm H2O. Conclusion: During VG ventilation with the Dräger Babylog 8000 the PIP was 4 cm H2O lower during triggered inflations than untriggered inflations, although the expired tidal volumes were similar.