Recognition that volume, not pressure, is the key factor in ventilator-induced lung injury and awareness of the association of hypocarbia and brain injury foster the desire to better control delivered tidal volume. Recently, microprocessor-based modifications of pressure-limited, time-cycled ventilators were developed to combine advantages of pressure-limited ventilation with the ability to deliver a more consistent tidal volume. Each of the modes has advantages and disadvantages, with limited clinical data available to judge their effectiveness. The Volume Guarantee mode has been studied most thoroughly and is the only one that provides automatic weaning of peak pressure in response to improving lung compliance and patient respiratory effort. More consistent tidal volume, fewer excessively large breaths, lower peak pressure, less hypocarbia and lower levels of inflammatory cytokines have been documented. It remains to be seen if these short-term benefits will translate into shorter duration of ventilation or reduced incidence of chronic lung disease.