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Variations in volume guarantee

Presented at the Neonatal Society 2005 Summer Meeting (programme).

Sharma A, Milner AD, Greenough A

Division of Asthma, Allergy and Lung Biology, Guy’s, King’s and St Thomas’ School of Medicine, King’s College London, Denmark Hill, London SE5 9RS, UK

Background: During volume guarantee (VG), the inspiratory pressure is automatically modified to achieve the set tidal volume. Preliminary evidence suggests VG may have advantages compared to “conventional” ventilation; these include maintenance of blood gases despite use of lower peak pressures and less episodes of desaturation. Preliminary evidence, however, suggests that the method of VG delivery is crucial to its efficacy.

Aim: To test the hypothesis that VG delivery would differ according to ventilator type.

Methods: An in vitro study was performed and three ventilators (Draeger Babylog 800 SLE 5000, and Stephanie paediatric ventilator) were assessed. Each ventilator was attached to a lung model, which had variable resistance and compliance. Between the lung model and ventilator a pneumotachograph was sited. Flow (integrated to volume) was measured from the pneumotachograph and peak (PIP) and mean airway pressure (MAP) were measured from a side aim on the pneumotachograph. The airway pressure waveform was also recorded. The ventilators were studied in SIPPV mode and a syringe was used to simulate patient breaths.

Results: At VG of both 5 and 10 mls, the peak pressure delivered by the ventilators differed significantly (Draegor vs Stephanie p = 0.04; Stephanie vs SLE p = 0.01), the MAP differed (Draeger vs Stephanie p = 0.001); Stephanie vs SLE p = 0.04) and the inspiratory time also differed (Stephanie vs SLE p = 0.01; Draeger vs SLE p = 0.01). These differences resulted from markedly different airway pressure waveforms delivered by the different ventilator types.

Conclusion: Before embarking on randomised studies to assess the long term outcome of VG, it is essential to determine which VG mode is most efficacious.

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