Aim Volume-targeted ventilation (VTV) improves outcomes in prematurely-born neonates with acute respiratory distress compared with pressure-limited modes.¹ The optimum level of tidal volume targeting (Vt), however, is undefined in infants remaining chronically ventilated with evolving or established BPD. In such infants it is important to ensure optimal growth by minimising their work of breathing (WOB). Our aim was to determine which Vt level was associated with the lowest WOB.

Methods A randomised, crossover study was performed of infants born at <32 weeks of gestation and mechanically ventilated beyond one week after birth. Each infant received twenty minute epochs of VTV at Vt levels of 4, 5, 6 and 7 ml/kg delivered in a random order, with a twenty minute period of pressure- limited baseline ventilation in between each Vt level. The WOB was assessed by measuring the pressure time product of the diaphragm (PTPdi). Recordings of flow, airway pressure and oesophageal and gastric pressures were made during the last five minutes of each epoch. PTPdi was derived by integrating the trans-diaphragmatic pressure (gastric pressure – oesophageal pressure) with time for each breath. The mean PTPdi for the first twenty artefact-free breaths is reported.

Results Nine infants were included with a median gestational age of 25 (range 24–28) weeks and birthweight of 788 (483–1190) gms). They were studied at a median corrected gestational age of 30 weeks. Their median PTPdi was 103 H₂O·s/min at baseline, 157 H₂O·s/min at 4 ml/kg, 108 H₂O·s/min at 5 ml/kg, 88 H₂O·s/ min at 6 ml/kg, and 78 H₂O·s/min at 7 ml/kg. The median PTPdi was significantly lower at a Vt of 6 ml/kg and 7 ml/kg compared with 4 ml/kg (p<0.001) and at a Vt of 7 ml/kg compared with 5 ml/kg (p=0.006).

Conclusion These results demonstrate that, in babies ventilated beyond one week of age, developing or with established BPD, a higher rather than a lower level of volume targeting reduces the work of breathing, this likely reflects the higher physiological dead space of such babies.

References

1. Klingenberg WK, et al. Cochrane Database of Systematic Reviews 2010, Issue 11. Art. No: CD003666