ICU · respiratory
Ventilator Waveforms — Comprehensive (Scalars, Loops, Asynchrony)
Also known as Ventilator waveforms · Scalar waveforms · Pressure-volume loop · Flow-volume loop · Patient-ventilator asynchrony · Double triggering · Auto-PEEP waveform · Flow-time waveform · Pressure-time waveform
Ventilator waveforms — the graphical display of pressure, flow, and volume over time during mechanical ventilation. Three SCALAR waveforms (pressure-time, flow-time, volume-time) and two LOOPS (pressure-volume, flow-volume) provide real-time information about patient-ventilator interaction, lung mechanics, and asynchrony. VOLUME CONTROL: square flow waveform + decelerating pressure + linear volume rise. PRESSURE CONTROL: square pressure + decelerating flow + curvilinear volume rise. P-V LOOP: compliance (slope = ΔV/ΔP), inflection points (lower = recruitment opportunity, upper = overdistension). F-V LOOP: auto-PEEP (expiratory flow doesn't return to baseline before next inspiration), obstruction (concave expiratory limb). PATIENT-VENTILATOR ASYNCHRONY: trigger asynchrony (missed triggers, auto-triggering), flow asynchrony (double triggering — patient wants more flow than delivered), cycle asynchrony (premature/delayed cycling), expiratory asynchrony. Waveform analysis is a CRITICAL CICM exam skill — tested in vivas and SAQs.
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Red flags
- Expiratory flow that does NOT return to baseline before the next inspiration = AUTO-PEEP (gas trapping) — reduce RR, shorten inspiratory time, increase expiratory time
- Double triggering = patient wants MORE flow than the ventilator is delivering — increase flow rate or switch to pressure support
- Missed triggers (patient effort not triggering a breath) = trigger sensitivity too insensitive OR auto-PEEP preventing triggering — adjust trigger or reduce auto-PEEP
Overview
References17ShowHide
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