In the previous tutorial I introduced some of the fundamental elements of pressure control ventilation – time cycling, decelerating flow, pressure ramps etc. This time I discuss, in detail, the concept of mean airway pressure (Pmaw) and describe why increasing Pmaw is an effective way of treating patients with extensive lung disease. In volume controlled ventilation this can be achieved by titrating PEEP upwards and increasing respiratory rate. Care must be taken to keep the plateau pressure below 30cmH2O in the majority of patients. In pressure control Pmaw is generally increased by increasing inspiratory time – extreme care must be taken, though, to avoid escalating Auto-PEEP as this corrodes tidal volume and actually reduces Pmaw.

If auto-PEEP is unavoidable, as it is with inverse ratio ventilation, then extrinsic PEEP should be reduced to ensure that tidal ventilation is maintained. Pmaw can be achieved in volume control by adding an inspiratory pause, and in pressure control by increasing respiratory rate – but these are less effective approaches – in volume control because of necessary flow limitation and in pressure control because of fixed inspiratory times, and Auto-PEEP.
I guarantee you’ll learn something.

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