A flow-time waveform shows expiratory flow failing to return to zero before the next breath is triggered during volume-controlled continuous mandatory ventilation (VC-CMV). What is the most appropriate action?

• A. Increase FiO2
• B. Switch to VC-IMV
• C. Switch to Pressure Support Ventilation
• D. Increase PEEP

Answer: (B)

expiratory flow failing to return to zero before the next breath is triggered signals incomplete exhalation and potential breath stacking with auto-PEEP. In a fixed, continuous volume mode, the ventilator delivers breaths at a set rate, which can leave too little time for full exhalation and lead to air trapping as the next inspiration slips in early.

Switching to VC-IMV helps because it reduces the number of mandatory breaths and allows spontaneous breathing between them. That longer gap gives the patient more time to exhale completely, minimizes air trapping, and reduces the risk that the next breath is triggered while expiration is still ongoing. It also lets the patient contribute breaths, improving synchrony with the ventilator.

Increasing FiO2 does not address the problem of expiratory time or auto-PEEP. Switching to pressure support could help with patient comfort and triggering, but it may not reliably resolve the expiratory time issue and could still contribute to breath timing problems. Increasing PEEP would worsen air trapping if exhalation isn’t complete.