Tidal Volumes Higher Than Desired on APV Cannot Be Fixed Simply By Transitioning to VC

Why switching from an adaptive mode to volume control to cap tidal volumes is not a straightforward solution.

APVVCMechanicsM2M5⤢ before / after

Problem.Initially patient was on APV and had signs of both early triggering and work shifting.

Fix #1

Early triggering resolved with decreasing rate. Note how: 1) airway pressures are almost flat and 2) tidal volumes are higher than target, despite the ventilator giving the lowest amount of pressure possible (3 cmH2O - right lower corner, under Pinp). These are classic findings of work shifting.

Fix #2

When switched to VC, the patient had profound work shifting/flow starvation. Note the extremely negative airway pressures as the patient tries to pull higher flows/volumes than the ventilator will allow. The best next step if we want tight control on tidal volumes is sedation with or without paralysis.