Southern African Journal of Critical Care

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A prospective comparison of the efficacy and safety of fully closed-loop control ventilation (Intellivent-ASV) with conventional ASV and SIMV modes

A Abutbul, S Sviri, V Zbedat, DM Linton, PV van Heerden


Background. Intellivent-adaptive support ventilation (ASV) is a  closed-loop, fully automatic method of mechanical ventilation. This advanced mode of ventilation adjusts ventilation and oxygenation  parameters according to patient weight, lung function (as assessed by the ventilator) and continuous input of end-tidal carbon dioxide and oxygen saturation. Our study compares the efficacy of this new mode with ASV and synchronised intermittent mandatory ventilation (SIMV) modes.
Methods. We conducted a within-group comparison of three modes of ventilation, ASV, Intellivent-ASV and SIMV, using a Hamilton S1 ventilator (Hamilton Medical, Switzerland). Subjects were ventilated for 2 hours on each mode, and at the end of each 2-hour period, parameters of ventilation and haemodynamics were measured.
Results. Twenty subjects participated in this study. Their mean age was 67.3 years (range 22 - 82 years). The most common diagnosis at presentation was pneumonia (55%), followed by chronic obstructive pulmonary disease (16%) and acute respiratory distress syndrome (11%). Mean (standard deviation) levels of positive end-expiratory pressure  (PEEP) were significantly higher in the Intellivent-ASV group (7.6 (5) v. 5.1 (2) and 5.2 (2) cm H2O in the ASV and SIMV groups, respectively  (p<0.005). Fractional inspired concentration of oxygen (FiO2) was  significantly lower in the Intellivent-ASV group (0.35 (0.7)) v. 0.41 (0.6) and 0.41 (0.6) for the ASV and SIMV groups, respectively (p<0.005). The mean spontaneous breathing rate in the Intellivent-ASV group was 8.6 (7.5) breaths per minute (b/min), significantly higher than in the ASV group (2.9 (5.7) b/min) and the SIMV group (2.4 (4.5) b/min) (p=0.002), while there was no difference in the total respiratory rate between the groups. There was no significant difference in haemodynamic parameters between the different ventilation modes. ASV tended to produce lower partial pressure of carbon dioxide (PCO2) levels than SIMV and  Intellivent-ASV (p<0.05).
Conclusions. Intellivent-ASV provided a significant reduction in the FiO2 with higher PEEP levels, but without haemodynamic detriment.  Intellivent-ASV encouraged significantly more spontaneous breathing, which may translate to faster weaning. Further studies to examine this effect are warranted.
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