Objective: To analyse the relationship between peak inflating pressure, expired tidal volume, respiratory rate, and inspiratory time of volume-guaranteed ventilator inflations and pressure-supported spontaneous breaths during synchronized intermittent positive pressure mode with volume guarantee and pressure support (SIMV-VG-PS) in neonates.
Methods: Ventilator parameters were downloaded every second from 16 babies ventilated with SIMV-VG-PS mode using Dräger Babylog VN500 ventilators over 137 days. Transcutaneous carbon dioxide (tcCO2 ) data were also collected. Data were computationally analysed using Python. The average of each ventilator parameter was determined during each minute separately for ventilator inflations and for spontaneous breaths. These values were compared and their effect on tcCO2 levels was also analysed.
Results: The relationship between the peak inflating pressure of the volume guaranteed inflations (PIPVG ) and pressure-supported spontaneous breaths (PIPPS ) was highly variable. The PIPPS /PIPVG ratio differed significantly from the value (0.66) targeted by clinicians (group median: 0.80, range: 0.50-1.00). PIPPS frequently exceeded PIPVG . When PIPPS /PIPVG was >0.66, the expired tidal volume and the rate of the pressure-supported spontaneous breaths were also significantly (p < 0.0001) higher, but there was no difference in tcCO2 levels. The flow-cycled spontaneous breaths had significantly shorter inspiratory times than ventilator inflations.
Conclusions: During SIMV-VG-PS it is difficult to ensure a pressure support level proportionate to the inflating pressure of ventilator inflations and to achieve the stability of tidal volumes.
Keywords: mechanical ventilation; neonatal intensive care; pressure support; synchronised intermittent mandatory ventilation; volume guarantee.
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