A concave pressure curve or a figure-8 shaped volume-time loop on a ventilator trace most commonly indicates which issue?

• A. Auto-PEEP
• B. Tube Leak
• C. Hypercapnia
• D. Air Hunger

Answer: (D)

The idea being tested is recognizing patient-ventilator asynchrony caused by the patient’s elevated inspiratory drive (air hunger). When a patient is actively fighting the ventilator, their own strong inspiratory effort can dominate the breath. On a pressure-time trace this shows up as a concave, or decelerating, rise in pressure during inspiration because the patient’s effort pulls on the airway more than the ventilator’s flow support can smooth out. In turn, the volume-time trace can take on a figure-8 shape when the patient continues to trigger breaths or double-triggers—breaths occur with overlapping efforts or near the end of one cycle, producing two small inflation phases that sketch a figure-8.

So these patterns point to air hunger and an under-supported patient drive, rather than a fixed issue like auto-PEEP, hypercapnia, or a simple tube leak. Auto-PEEP tends to show breath-stacking patterns or altered expiratory flow, hypercapnia is a gas-exchange state not a waveform pattern, and a tube leak changes tidal volume and flow but not the characteristic concave and figure-8 shapes described.