Using Pressure Assist-Control Ventilation

Although the use pressure control is increasing in popularity in the setting of acute lung injury, it is a versatile mode that can be used, if the practitioner is skilled, on any intensive care patient. There is no evidence that pressure control is superior to volume control. Nonetheless the ability to easily control inspiratory time, allows to more effective management of mean airway pressure. Pressure limited ventilation may also lead to better gas distribution, although the same effect can be achieved in volume control by altering flow rates and inspiratory pause.

Set PEEP as  in protocol (click here)

Set initial rate at 12-14 breaths/minute

Adjust inspiratory pressure (IP) to obtain a tidal volume of  at 6ml/kg Start high (lung recruitment) and work downwards

Set initial inspiratory time at 0.5 to 0.8 seconds Set flow triggering Look at pressure waveform, adjust inspiratory flow (slope) to optimal setting.

Check a blood gas after 30-60 minutes If CO2 is elevated increase the respiratory rate but be careful of auto-PEEP (click here) If hypoxemia improving reduce the driving (inspiratory) pressure

If the patient develops severe hypoxemia increase the PEEP as necessary increase the inspiratory time to 1.0 to 1.5 seconds sedate and paralyse the patient consider prone positioning consider alternative modes:  ARPV  HFO

Be very careful of auto-PEEP (click here): reduced tidal volume for IP If hypercarbia  is the primary problem reduce inspiratory time If hypoxemia is primary problem reduce respiratory rate and allow permissive hypercapnea

Is the patient breathing spontaneously? Reduce the controlled rate until the patient is on pressure assist (the patient triggers the breath only) If respiratory drive intact, and lung injury is not advancing, consider switching the patient over to pressure support ventilation (PSV).

If the patient is not ready to control the rate, depth and duration of breath, and is tachypneic: increase the sedation consider BiLevel (or equivalent) ventilation.

If switching to PSV: set the pressure support to the inspiratory pressure (in PC)

Look at pressure waveform, adjust inspiratory flow (slope) to optimal setting.

Watch lung compliance: increase PS if compliance reduces (decreased tidal volumes) decrease PS if compliance improves (tidal volumes >6ml/kg).

Address patient sedation (tachypnea in PSV is often from inadequate sedation) Beware of tachypnea with small tidal volumes (click here)