In time-cycled synchronized intermittent mandatory ventilation (SIMV), synchrony between mechanical and spontaneous breath occurs during:

• A. Expiration only
• B. Inspiration only
• C. Inspiration and expiration
• D. None

Answer: (B)

In SIMV, the ventilator provides breaths at a set rate but also monitors the patient’s own efforts to breathe. Synchrony is achieved when the ventilator detects a spontaneous inspiratory effort and aligns its assisted inspiratory phase with that effort, delivering support right as the patient starts to inspire. The inspiratory phase is where coordination matters most, because the machine must time its inspiration to the patient’s draw of air. Expiration isn’t synchronized in the same way, since it follows the end of inspiration and the ventilator’s cycles don’t actively time the expiratory phase to the patient’s effort. So the synchrony occurs during inspiration only.