Emphasis during mechanical ventilation of the most critically ill has focused in recent years on preventing further lung injury by the approach used to provide ventilatory support. Inverse ratio ventilation fits nicely into a lung protective ventilatory strategy since it emphasizes the use of pressure ventilation and the targeting of low peak alveolar pressure. However, no controlled, prospective data is available to support the superiority of inverse ratio ventilation regardless of target (pressure or volume) or actual inspiratory:expiratory (I:E) ratio when compared to conventional ratio ventilation. The current published data shows equivalence in gas exchange, hemody-namics and compliance regardless of approach used. Once positive end-expiratory pressure PEEP is set above the lower infection point on the pressure-volume curve of the lung, extending inspiratory time to increase mean airway pressure and oxygenation is a reasonable method of improving oxygenation provided auto-PEEP does not develop, since peak alveolar pressure is maintained constant. Emphasis should be on achieving an oxygenation target by increasing mean airway pressure not establishing a specific I:E ratio. In general most patients can be successfully managed with I:E ratios ⩽1:1.