Mechanical inspiratory peak flow as a determinant of tidal volume during IMV and PEEP

With some circuits, during intermittent mandatory ventilation (IMV) with high positive end-expiratory pressure (PEEP), increased inspiratory effort is needed to overcome the pressure gradient across the unidirectional IMV valve, so as to allow its opening for spontaneous breathing. Increasing positive pressure in the spontaneous breathing circuit (SBC) of the IMV system can greatly reduce this inspiratory effort. When such positive pressure is created in the SBC by a high continuous flow into this circuit, the delivered mechanical tidal volume depends greatly on the mechanical inspiratory peak flow (MPIF) of the respirator, lower MIPF's being associated with larger tidal volumes. Low MIPF's are, in turn, often used in combination with high PEEP to reduce peak mechanical inspiratory pressures (PMIP) and thus reduce the danger of barotrauma.