Adaptive support and pressure support ventilation behavior in response to increased ventilatory demand

Abstract

BACKGROUND: Dual-control modes of ventilation adapt the pressure delivery to keep a volume target in response to changes in respiratory mechanics, but they may respond poorly to changes in ventilatory demand. Adaptive support ventilation (ASV), a complex minute volume-targeted pressure-regulated ventilation, was compared to adaptive pressure ventilation (APV), a dual-mode in which the pressure level is adjusted to deliver a preset tidal volume, and to pressure support ventilation (PSV) when facing an increase in ventilatory demand. METHODS: A total of 14 intensive care unit patients being weaned off mechanical ventilation were included in this randomized crossover study. The effect of adding a heat-and-moisture exchanger to augment circuit dead space was assessed with a same fixed level of ASV, PSV, and APV. RESULTS: Arterial blood gases, ventilator response, and patient respiratory effort parameters were evaluated at the end of the six periods. Adding dead space significantly increased minute ventilation and Paco 2 values with the three modes. Indexes of respiratory effort (pressure-time index of respiratory muscles and work of breathing) increased with all ventilatory modes after dead-space augmentation. This increase was significantly greater with APV than with PSV or ASV (P < 0.05). The assistance delivered during APV decreased significantly with dead-space from 12.7 ± 2.6 to 6.7 ± 1.4 cm H2O, whereas no change occurred with ASV and PSV. CONCLUSIONS: ASV and PSV behaved differently but ended up with similar pressure level facing acute changes in ventilatory demand, by contrast to APV (a simple volume-guaranteed pressure-control mode), in which an increase in ventilatory demand results in a decrease in the pressure support provided by the ventilator.