Oct 242011

Adaptive support ventilation (ASV) has entered wide use based on its attractive premise: it's patient-centered ventilation, adapting breath-by-breath to deliver precisely the right amount of pressure support to achieve a targeted minute ventilation. However, evidence for any superiority over conventional ventilator modes is limited to cardiac surgery patients who were extubated in ~6 hours regardless of the mode used (but faster with ASV).

In heavy-duty, hard-to-wean patients, there's no known benefit to ASV. And in acute lung injury and ARDS, machines set on ASV's internal work-of-breathing equation routinely and blithely exceed 8 mL/kg tidal volumes, inducing shudders in pulmonary physicians.

Kirakli et al randomized 97 patients with COPD and respiratory failure who were ready to wean to either go on ASV with stepwise reduction in minute ventilation support, or on pressure support ventilation in stepwise reductions. Patients went on a spontaneous breathing trial when they completed the step-down wean. This was at a single tertiary care center in Izmir, Turkey.

Patients on ASV were extubated in 24 hours; those on PSV took 72 hours (p=0.04). ICU lengths-of-stay were non-significantly lower in the ASV group.

Very interesting. But why weren't the patients who were ready to wean tried on an SBT or T-piece and extubated straightaway if they passed? And placed into this protocol if they didn't pass the SBT?

Authors indirectly acknowledge that would be the standard (by noting that PSV weans have been proven inferior to T-piece and are not the standard). The only thing I can think of is, maybe they were concerned they wouldn't have had enough patients if they had done it that way? (They started with 435 and excluded all but 97 for various reasons.) They rightfully recommend a multicenter randomized trial, which would be great to establish an indication, because IMHO, ASV does seem like a good mode to use in patients without ARDS.

Kirakli C et al. Adaptive support ventilation for faster weaning in COPD: a randomised controlled trial. Eur Resp J 2011;38(4):774-780.

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Adaptive support ventilation weaned COPD patients faster than pressure support