Standard vs Alternative Vent Modes: What’s the Difference?

Abstract

Pressure-control ventilation and APRV, a form of PCV, have similar breath delivery patterns (square wave) that allow early and sustained achievement of the set inspiratory pressure until exhalation. This breath pattern combined with inverse ratio (short expiratory time) can reexpand the collapsed lung areas associated with ARDS.Yes. Continuous lateral rotation using rotational sleep surfaces supports expansion of collapsed alveoli. We also use prone positioning for patients with refractory hypoxemia resulting from alveolar collapse to expand alveoli in the posterior regions, often in conjunction with inhaled pulmonary vasodilators. This combination improves the ventilation-perfusion matching; even in the prone position, the majority of pulmonary perfusion tends to be in the posterior lung. The perfusion now aligns better with recruited alveoli in the posterior region.Placing the patient in the prone position helps to recruit collapsed alveoli in the posterior segments, improving ventilation to these regions. In the prone position, pressure on the anterior chest wall can limit expansion, resulting in increased peak inspiratory pressure in volume-controlled ventilation. If the patient is receiving PCV, this limit in chest wall expansion may result in decreased tidal volumes after proning, as the set inspiratory pressure limit may be reached sooner as a result of chest wall restriction. Conversely, as lung units are recruited with the patient prone, tidal volumes in PCV may increase as lung compliance improves. Once the patient is prone, lung mechanics should be evaluated and tidal volumes and inspiratory pressure limits adjusted accordingly. Positive end-expiratory pressure may need to be increased, as well. Mobilization of pulmonary secretions may also compromise ventilation, so suctioning may be necessary. Both volume-controlled ventilation and PCV strategies are acceptable.