DEMAND-FLOW AIRWAY PRESSURE RELEASE VENTILATION AS A PARTIAL VENTILATORY SUPPORT MODE - COMPARISON WITH SYNCHRONIZED INTERMITTENT MANDATORYVENTILATION AND PRESSURE SUPPORT VENTILATION

Objective: To evaluate airway pressure release ventilation as a partia l ventilatory support mode by comparing a demand-flow airway pressure release ventilation system with synchronized intermittent mandatory ve ntilation and pressure support ventilation. Design: Prospective, nonra ndomized, crossover trial. Setting: Medical intensive care unit in a u niversity medical center. Patients: Sixteen consecutive patients witho ut chronic obstructive pulmonary disease with mechanical ventilatory s upport of 25% to 75% of total minute ventilation on synchronized inter mittent mandatory ventilation, or 25% to 75% of maximal pressure suppo rt level on pressure support ventilation. Interventions: Each mode of mechanical ventilation was supplied to patients with comparable levels of partial support for 30 mins. Measurements and Main Results: Among three different modes, demand-flow airway pressure release ventilation achieved the lowest peak airway pressure (airway pressure release ven tilation 9.1 +/- 2.6 cm H2O; pressure support ventilation 18.4 +/- 4.6 cm H2O; synchronized intermittent mandatory ventilation 34.8 +/- 7.7 cm H2O; p <.001). Hemodynamic status and oxygenation status were simil ar among these three modes. Five (31%) of the 16 patients felt that de mand flow airway pressure release ventilation was a less comfortable m ode than synchronized intermittent mandatory ventilation or pressure s upport ventilation. This finding had no clear correlation with their d uration of airway pressure release, preset machine deflation rate, or inspiratory/expiratory ratio of machine breath. Gross asynchrony of ef fort and ventilator cycling was noticed in two (13%) patients while th ey were receiving demand-flow airway pressure release ventilation. Con clusions: We conclude that for patients who do not have chronic obstru ctive pulmonary disease, demand-flow airway pressure release ventilati on can provide effective partial ventilatory support with lower peak a irway pressure when compared with pressure support ventilation and syn chronized intermittent mandatory ventilation. However, this airway pre ssure release ventilation system may be less comfortable than the othe r two modes, and asynchrony may occur in some patients.