Recognition that volume, not pressure, is the key factor in ventilator-induced lung injury and the association of hypocarbia and brain injury dictate the need to better control delivered tidal volume. Volume-controlled ventilation, though much improved, still suffers from loss of volume due to endotracheal tube leak and gas compression in the circuit. Recent microprocessor-based modifications of pressure-limited, time-cycled ventilators 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 data available to judge their effectiveness. The Volume Guarantee mode, studied most thoroughly, provides automatic weaning of peak pressure in response to improving lung compliance and 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 translate into shorter duration of ventilation or reduced incidence of chronic lung disease.