Inverse ratio ventilation

In inverse ratio ventilation the inspiratory-to-expiratory (I:E) ratio set on the ventilator is greater than 1:1, i.e. inspiratory time is longer than expiratory time. The short expiratory time used in this mode, despite the absence of external positive end-expiratory pressure (PEEP), prevents the collapse of alveoli during expiration due to gas trapping and generation of intrinsic PEEP (auto-PEEP).

In single-compartment systems, the time needed to exhale 96 per cent of the inspired tidal volume is equal to three time constants (the product of resistance and compliance). Consequently, if expiratory time is too short, dynamic hyperinflation will be generated and some level of intrinsic PEEP will be present. Inverse ratio ventilation can be used in volume- or pressure-controlled modes. Typical tracings obtained during inverse ratio ventilation are shown in Fig 1 and Fig.2.

Fig. 1 Tracings of airflow (flow), airway pressure ( Paw), and tidal volume obtained in a patient ventilated with pressure-controlled inverse ratio ventilation (I:E ratio,

Fig. 1 Tracings of airflow (flow), airway pressure ( Paw), and tidal volume obtained in a patient ventilated with pressure-controlled inverse ratio ventilation (I:E ratio,

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