Ventilator monitor. Computer-enhanced image of a ventilator monitor in an intensive care unit. This machine is ventilating the lungs of a patient who is unable to breathe unaided. It is shown in BIPAP (bi-level positive airway pressure) mode, forcing air into the patient's lungs. The graph (black) at centre left shows air pressure variation over two breathing cycles. Vital quantities being monitored include: FIO2 (fraction inspired oxygen) and PEEP (positive end-expiratory pressure), the residual pressure keeping the lungs open. Other ventilation mode buttons are at lower right. SIMV (synchronous intermittent mandatory ventilation) synchronises ventilation with a patient's efforts to breathe.