Reading the waveforms and managing the ventilator, built on one equation and a formal taxonomy.
Provide safe gas exchange.
Foster patient–ventilator synchrony.
Optimize the weaning experience.
The goals are not equally weighted: in acute failure safety dominates; as the patient stabilizes comfort matters more. Every setting choice serves one of these three. [Mireles-Cabodevila 2013]
At every instant, the pressure from the patient's muscles plus the ventilator must overcome the elastic load (elastance E = 1/compliance, times volume) and the resistive load (resistance × flow).
Everything downstream — modes, waveforms, patient–ventilator interaction — is read off this one balance. [Mireles-Cabodevila 2025]
Together these give a mode's TAG — e.g. PC-CMVa. Classify a mode by what it does, not its brand name.
This taxonomy is a proposed standard the authors advocate, not universally adopted nomenclature. [Chatburn 2014; Mireles-Cabodevila 2022]
Whatever you set becomes a clean square wave and tells you nothing about the patient. Setting volume alone, or flow alone, is not volume control.
Continuous mandatory. Spontaneous breaths are not possible between mandatory breaths; set frequency is a minimum.
Intermittent mandatory. Spontaneous breaths are possible between mandatory ones; set frequency is a maximum. Five types.
Continuous spontaneous. Every breath is patient-triggered and patient-cycled.
Control variable (2) × breath sequence (3) → five patterns: VC-CMV, VC-IMV, PC-CMV, PC-IMV, PC-CSV. VC-CSV is impossible — volume control implies ventilator cycling, which makes every breath mandatory. [Chatburn 2014]
| Scheme | What it does | Example |
|---|---|---|
set-point (s) | Operator sets every parameter of the waveform; fixed settings | Conventional VC, PC, PSV |
dual (d) | Switches between volume and pressure control within one breath | VAPS, PA |
bio-variable (b) | Randomly varies pressure/VT to mimic natural breathing variability | Variable PS / noisy ventilation |
servo (r) | Output follows a varying input — pressure proportional to effort | PAV, NAVA, ATC |
adaptive (a) | Sets one target between breaths (pressure) to hit another (average VT) | PRVC, VC+, AutoFlow |
optimal (o) | Adjusts targets to minimize work rate of breathing | ASV |
intelligent (i) | Adjusts targets with AI (rule-based, fuzzy logic, neural nets) | SmartCare/PS, IntelliVent-ASV |
We use ASV (optimal targeting) here — so the next slides elaborate on set-point, servo, adaptive, and optimal. [Chatburn 2014; Mireles-Cabodevila 2013]
Drive the patient's effort up and watch the airway pressure in each scheme.
These display signatures let you name the targeting scheme at the bedside. [Chatburn 2026, waveform method]
Optimal targeting adjusts the whole ventilatory pattern to minimize an overall cost — here the work rate of breathing. For a required alveolar ventilation, very slow breaths cost elastic work (big VT) and very fast breaths cost resistive work; there is a rate in between that costs the least.
ASV picks the rate at the minimum of this curve and sets VT to match — then re-optimizes breath to breath.
Illustrative model of the optimal-targeting principle; ASV is optimal targeting on a PC-IMV chassis. [Chatburn 2014; Mireles-Cabodevila 2013]
PRVC / VC+ / AutoFlow / “volume guarantee” set a tidal-volume target but control pressure breath-to-breath, adjusting it between breaths to hit an average VT.
By behaviour they are PC-CMVa — pressure control, CMV, adaptive targeting — not the volume mode the brand name suggests.
You cannot read the waveforms until you know what the ventilator is actually programmed to do. The TAG tells you.
PC-CMVa[Mireles-Cabodevila 2022, method to read waveforms; Majumdar 2025]
[Chatburn 2014, 10 fundamental maxims]
[Chatburn 2014, 10 fundamental maxims]
You set volume & flow →
read the load off PRESSURE
You set pressure →
read the load off FLOW & VOLUME
Walk the eight reference points — Pinit, Ppeak, Pplat, V̇peak-insp, V̇end-insp, V̇peak-exp, V̇end-exp, VT — and say whether the load is resistive, elastic, or whether Pmus is present. [Chatburn 2026]
Constant inspiratory flow makes airway pressure a resistive step (R·V̇) sitting on top of an elastic ramp (V/C).
An inspiratory hold (zero-flow) reveals Pplat and splits the two loads.
In VC the inspiratory flow is set — it stays square regardless of mechanics. The patient shows up in the pressure: effort pulls it concave (flow starvation).
Pressure is the square wave, so the patient shows up in flow & volume. Peak inspiratory flow = ΔP / R — set by the pressure and resistance, independent of compliance.
Change compliance and the peak does not move: what changes is the decay slope (τ = R·C) and the tidal volume it fills to.
Expiration is passive: flow decays on the time constant. If the next breath starts before the lung empties (Te < ~3τ), the expiratory flow does not return to zero — gas is trapped and auto-PEEP builds.
Watch V̇end-exp lift off the zero line as you speed the rate — the peak barely moves, but the slope and the trapping do.
trigger → inspiration → cycle → expiration
Trigger and cycle are judged for timing; inspiration and expiration for the work relationship.
Reference signal is the patient's effort, Pmus (Pes / EAdi, or inferred from the waveforms).
[Mireles-Cabodevila 2022, 2026]
[Mireles-Cabodevila 2026, defining & measuring PVI]
[Mireles-Cabodevila 2026, defining & measuring PVI]
| Term | Definition |
|---|---|
| Synchrony | Near-zero phase difference between the patient signal and the ventilator response |
| Asynchrony | Absence of a ventilator response to a patient signal, or vice versa (a missing signal) |
| Dyssynchrony | A clinically important timing difference between patient signal and ventilator response |
| Work shifting | Pvent and Pmus are active together and both contribute to the work done (magnitude) |
Keep timing (dys/asynchrony) and magnitude (work shifting) distinct. [Mireles-Cabodevila 2022, 2026]
Δt = tvent − tmus
Δt < 0 → early · Δt = 0 → synchronous · Δt > 0 → late
Failed triggering is the classic consequence of dynamic hyperinflation — relieve the auto-PEEP.
[Mireles-Cabodevila 2026; Chatburn 2020]
When the patient and ventilator share the work, the tell depends on the control variable:
Work shifting is not inherently abnormal and can occur with perfect timing. [Mireles-Cabodevila 2026]
Ventilator stops before the effort ends.
The continuing effort can pull a second breath — double triggering / breath stacking. A leading cause of injurious large tidal volumes.
Ventilator keeps pushing after the effort ends.
The patient exhales against ongoing inspiratory pressure; wasted work, discomfort, and dynamic hyperinflation.
Flow-cycling threshold (in PSV), inspiratory time (in PC), and effort together set where the cycle lands. [Mireles-Cabodevila 2022; Liu 2024]
Summarize the whole state in one sentence — e.g. “PC-CMVa, high elastic load, early triggers” — then choose the single primary goal:
Not every discordance needs a fix; mild work shifting often doesn't. When discordances are linked, report and treat the first in the chain.
[Mireles-Cabodevila 2022, one-page waveform-analysis tool]
Four virtual patients. In your groups, read the waveforms and vitals, choose a management step, and see how the patient responds — then reach a debrief. ARDS · severe obstruction · dyssynchrony · the post-intubation crash.
Scenario console → vent-megacode.pages.dev
Everything in this hour, written to read top-to-bottom — plus the interactive simulator the figures come from.
vent-waveforms.pages.dev
Figures and concepts adapted from the published mechanical-ventilation work of R.L. Chatburn & E. Mireles-Cabodevila. Educational reference; not a medical device; not for clinical use.