Five modes, live physics. Pick a mode (VC-AC, PC-AC, PRVC, SIMV, APRV), pick a problem, and adjust the ventilator settings until you fix it. Pressure, flow, and volume waveforms are computed in real time from a single-compartment respiratory mechanics model — every problem can be created and resolved with the on-screen controls.
Sandbox — you set VT and flow; pressure is the result. Stiffen the lungs (↓compliance) and watch PIP and plateau climb. Try RR 30 with a low flow and create auto-PEEP by accident.
Simulated waveforms for education — an idealized single-compartment model, not patient data. SIMV spontaneous breaths and APRV oscillations are stylized. Not a substitute for clinical judgment or your institution's protocols.
Airway pressure in cmH₂O. The shape tells you the mode: ramp = VC, square = PC/PRVC. PIP is the peak; plateau is the static stretch pressure after an inspiratory hold. The gap between them is resistance × flow.
Gas velocity in L/min. Square = volume-controlled (fixed delivery). Decelerating = pressure-controlled (variable, demand-following). Expiratory flow is always passive — its speed and shape encode compliance and resistance.
Cumulative inhaled volume above PEEP. Should return to zero each breath. If it doesn't fully empty, auto-PEEP is building. A plateau above zero that drops vertically is a leak — VTe < VTi.
| Pattern | Key waveform finding | Fix |
|---|---|---|
| Normal VC | Square flow, ramp pressure, linear volume → zero | — |
| Normal PC / PRVC | Square pressure, decelerating flow, curved volume → zero | — |
| Auto-PEEP | Exp. flow never returns to zero; total PEEP > set PEEP | ↓ Rate, ↓ VT/Ti, treat obstruction |
| Double triggering | Two breaths stacked; second breath begins before exp. flow ends | ↑ Ti (VC: ↓ flow), address drive |
| Flow starvation (VC only) | Concave scoop in pressure; flow stays square; volume normal | ↑ Set flow or switch to PC/PRVC |
| Secretions | Sawtooth on flow; VC: ↑ PIP–Pplat gap; PC: ↓ VTe | Suction, drain circuit condensate |
| Leak | VTe < VTi; volume never reaches zero; PEEP drifts ↓ | Check cuff, circuit, chest tube |
A sawtooth (jagged, serrated) pattern on the flow scalar — both inspiratory and expiratory — is the signature of secretions or condensate vibrating in the airway. In volume-controlled modes, PIP rises while the plateau stays normal, widening the PIP–Pplat gap. That gap means resistance, not stiff lungs. In pressure-controlled modes, delivered VT quietly falls.
The most reliable sign in any mode: expiratory flow fails to return to the zero baseline before the next breath begins. Volume doesn't fully empty, and total PEEP reads above set PEEP. In VC modes, PIP and plateau creep upward breath by breath. In PC/PRVC modes, the pressure trace looks normal but delivered VT quietly falls as trapped gas steals driving pressure.
Double triggering occurs when the patient's neural inspiratory time outlasts the set Ti — the vent cycles off while the patient is still inhaling, and the continued inspiratory effort immediately triggers a second breath. Volume stacks: in VC the second breath can reach nearly double the set VT; in PC the mode self-limits because trapped volume reduces the effective driving pressure.
A concave (inward scoop) in the pressure scalar during inspiration on volume-controlled ventilation is flow starvation: the patient's inspiratory demand exceeds the set flow. Vigorous effort drops airway pressure mid-breath, carving the scoop. The flow waveform stays square — that rigidity is the problem. Fix: increase set flow, or switch to a pressure-targeted mode.
When VTe < VTi, gas is escaping before it reaches the expiratory sensor — a circuit leak. Common causes: cuff underinflation or leak, loose circuit connection, water trap or humidifier leak, chest tube / bronchopleural fistula, or mask leak on NIV. The volume scalar plateaus above zero and the PEEP drifts below the set value.
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