A mode describes a predetermined pattern of patient–ventilator interaction — so choosing a mode is choosing which goal to serve. That is what the taxonomy lets us do precisely. [Mireles-Cabodevila 2013]
The one idea
Everything a ventilator does balances one equation
Pmus + Pvent =
E · V + R · V̇ + PEEP
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).
C = 1/Ecompliance — how easily the lung fills
Rresistance — how hard gas moves
τ = R · Ctime constant — how fast it empties
Modes, waveforms, and patient–ventilator interaction all read off this one balance. [Mireles-Cabodevila 2025]
The screen is graphing that equation
Three variables, drawn three ways
Pressure, flow and volume are the one equation plotted over time.
Pressure = elastic + resistive, above PEEP
Flow = rate of change of volume
Volume = integral of flow
Learn the normal shapes; every finding is a deviation.
PressureFlowVolume
Naming a mode · the first axis — control variable [maxim 3]
Volume control vs. pressure control
Set a square flow (and VT) → Volume control
Set a square pressure → Pressure control
Whatever you set becomes a clean square wave and tells you nothing about the patient.
The second axis — breath sequence · how a breath is formed [maxims 1, 4, 5]
Every breath has a trigger and a cycle
Trigger — a signal (time, or the patient's effort) starts inspiration.
Cycle — a signal (a set time, or % of peak flow) ends it.
Each can be ventilator- or patient-driven. Flow-cycling counts as patient cycling.
Breath sequence · mandatory vs spontaneous [maxim 6]
Who triggers and who cycles classifies the breath
Mandatory — ventilator triggers and/or cycles
Time-triggered, time-cycled. Assisted by definition (e.g. an A/C breath).
Spontaneous — patient triggers and cycles
Patient owns both events, independent of the machine's timing (e.g. pressure support).
A breath the patient starts but the ventilator ends is still mandatory. Only when the patient owns both is it spontaneous.
Breath sequence · CMV / IMV / CSV [maxims 7, 8]
Three sequences, seen on the tracing
CMV
All breaths mandatory; no spontaneous between. Set rate is a minimum.
IMV
Mandatory breaths plusspontaneous ones between. Set rate is a maximum.
CSV
Every breath spontaneous — patient-triggered and patient-cycled.
2 control variables × 3 sequences → five patterns; VC-CSV is impossible. [Chatburn 2014]
The third axis — targeting scheme [maxim 9]
How the machine hits its target: seven schemes
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
bio-variable (b)
Randomly varies pressure/VT to mimic natural breathing variability
Variable / noisy PS
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+, APV-CMV
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 elaborate on set-point, servo, adaptive, and optimal (ASV) next. [Chatburn 2014; Mireles-Cabodevila 2013]
Interactive · reading the targeting scheme off the waveform
What patient effort does to the pressure
Set-point— height never moves (independent of R, C, effort)
Adaptive— pressure falls as effort rises (holds average VT)
Servo— pressure proportional to effort (PAV, NAVA)
Optimal targeting — the mode we use (ASV)
ASV minimizes the work rate of breathing
Optimal targeting adjusts the whole 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; a rate in between costs the least.
ASV picks the rate at the minimum and sets VT to match, then re-optimizes breath to breath.
–optimal rate
–resulting VT
Work rate vs. respiratory frequency (Otis)
Name the mode by what it does [maxim 10]
“Volume control” that is really pressure control
PRVC · VC+ · APV-CMV · 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 — not the volume mode the brand name suggests.
You cannot read the waveforms until you know what the ventilator is programmed to do. The TAG = control + sequence + targeting tells you.
Its real classification:
PC-CMVa
control · sequence · targeting
[Mireles-Cabodevila 2022; Majumdar 2025]
What we just built · the ten fundamental maxims
The ten constructs behind the taxonomy
A breath is one cycle of inspiratory then expiratory flow.
A breath is assisted if the ventilator does some or all of the work.
Assistance is either pressure control or volume control (the control variable).
Breaths are classified by what triggers and cycles inspiration.
Trigger and cycle can be patient- or ventilator-initiated.
A breath is spontaneous (patient triggers & cycles) or mandatory.
Three breath sequences: CMV, IMV, CSV.
Two controls × three sequences → five patterns (no VC-CSV).
Within a pattern, types differ by their targeting scheme (seven).
A mode = control variable + breath sequence + targeting — its TAG.
[Chatburn 2014, ten fundamental maxims]
Reading the waveform · the load
Read the load opposite the control variable
VC
You set volume & flow → read the load off PRESSURE
PC
You set pressure → read the load off FLOW & VOLUME
Whatever you set is a flat square and carries no information; the patient lives in the other waveform. [Mireles-Cabodevila 2022]
Interactive · anatomy of a VC breath
Constant flow → a resistive step on an elastic ramp
The inspiratory flow is set (square); the load shows in the pressure. An inspiratory hold reveals Pplat:
Ppeak − Pplat = resistive pressure (R·V̇)
Pplat − PEEP = elastic pressure (VT/C)
–peak (PIP)
–plateau
–τ = R·C
PressureFlowPmus effort
Interactive · pressure control & the time constant
Peak flow is pinned at ΔP/R; mechanics change the slope (τ)
FlowVolumefixed axes
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. Flow decays over about 3τ.
When expiratory time < ~3τ, flow can’t reach zero → auto-PEEP
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.
–expiratory time
–3τ needed
–auto-PEEP
R and C are fixed here, so the peak and slope don’t change — only the expiratory time shrinks. Watch the flow fail to reach zero. Fix: slow the rate, lengthen expiration.
FlowVolume
A bedside use of the waveform
High peak-pressure alarm: one inspiratory hold sorts it
PIP high & Pplat high → compliance problem
Small peak–plateau gap. Pneumothorax, edema/ARDS, atelectasis, abdominal pressure, breath stacking.
The peak-to-plateau gap is the resistive pressure — the same R·V̇ term from the equation of motion.
The safety goal · avoid VILI
Keep plateau and driving pressure in range
Tidal volume 4–8 mL/kg predicted body weight
Plateau pressure < 30 cmH₂O (alveolar stretch)
Driving pressure (Pplat − PEEP) < ~15 cmH₂O
Enough PEEP to keep alveoli open
–plateau
–driving pressure
PressureVolume
[Mireles-Cabodevila 2013; El-Khatib 2024]
Patient–ventilator interaction [PVI maxims 1–3]
When the patient shows up on the tracing
The reference signal is the patient's effort, Pmus (esophageal pressure, EAdi, or inferred from the waveforms). Interaction has two axes:
Timing — the phase difference Δt between Pmus and Pvent. Synchrony = Δt ≈ 0.
Magnitude — the work balance: who is doing the work.
In VC, effort scoops the pressure concave — flow starvation.
PressurePmus effort
Magnitude · assistance is a continuum [PVI maxim 9]
How much of the work should the ventilator do?
The Work-Shifting Index is the share of the total work done by the patient: 0% = ventilator does all the work, 100% = patient does all of it, >100% = the effort overrides the ventilator (loaded, unproductive breaths).
0% — ventilator all workgoal-appropriate100%+ — patient all work
Over-assistance
Low work shifting. Muscle unloading → diaphragm atrophy, and promotes failed triggers.
Goal-appropriate
Enough support for the current goal — safety early, comfort/conditioning later.
Under-assistance
High work shifting. Distress, fatigue, and risk of self-inflicted lung injury.
The acceptable amount depends on the goal. [Mireles-Cabodevila 2026]
Inspiration · three states [PVI maxim 7]
Who is generating the inspiratory force?
Unassisted
Pmus only — the patient does all the work; the ventilator adds nothing.
Passive-assisted
Pvent only, Pmus = 0 — a fully controlled breath.
Active-assisted
Both together — shared work. This is where work shifting lives.
[Mireles-Cabodevila 2026, PVI maxims]
Expiration · four states [PVI maxim 10]
Expiration is not always just passive recoil
Passive
Elastic recoil only; flow decays to zero.
Active
Expiratory muscles (Pmus < 0) push gas out faster.
Assisted
Ventilator drops pressure below PEEP to aid exhalation.
Controlled
Ventilator regulates the expiratory flow waveform (passive patients).
Detailed derivations sit in the paper's appendix. [Mireles-Cabodevila 2026]
Magnitude · work shifting [PVI maxim 8]
The same effort looks different by control variable
VC — pressure scoops
PC — flow & VTrise
Adaptive — pressure backs off
Work shifting is not inherently abnormal and can occur with perfect timing. [Mireles-Cabodevila 2026]
Timing · the trigger phase [PVI maxims 5, 6]
Trigger discordances — the breath vs. the effort
Synchrony
Breath and effort start together (Δt ≈ 0).
Early / reverse
Machine breath precedes the effort; the effort follows by entrainment.
False trigger
A breath with no Pmus (cardiogenic, condensate, leak).
Failed trigger
Effort that doesn't trigger — often from auto-PEEP.
Δt = tvent − tmus: negative = early, zero = synchronous, positive = late. Reverse triggering is a type of early trigger. [Branson & Chatburn 2026]
Timing · the cycle phase [PVI maxim 5]
Cycle discordances — and their consequence
Early cycle → double trigger
Machine stops before the effort ends → a second stacked breath. A leading cause of injurious large VT.
Late cycle
Machine keeps pushing after the effort ends → active exhalation, wasted work, hyperinflation.
Late trigger
The breath lags the effort. On modern ventilators (<80 ms) rarely felt.
Double / multiple triggering is a consequence of early cycle, early trigger, or flow discordance — not a primary type. [Branson & Chatburn 2026]
The PVI framework · ten maxims
Defining and measuring the interaction
The equation of motion is the foundation — who generates force, and when.
Patient effort Pmus is the reference signal.
Two axes: timing (phase) and magnitude (work shifting).
Synchrony = zero phase difference at trigger, cycle, and peak.
4 · Intervene. Pick the single primary goal — safety, comfort, or liberation — then adjust settings, change the mode, or do nothing. Many interactions are temporary and harmless. [Mireles-Cabodevila 2022]
Two things to take with you
Run the mega-code · read the full guide
Ventilation mega-code
vent-megacode.pages.dev
Four branching scenarios you run in your groups.
Full guide + simulator
vent-waveforms.pages.dev
Everything in this hour, plus the interactive simulator.
Figures & concepts adapted from the published mechanical-ventilation work of R.L. Chatburn & E. Mireles-Cabodevila. Not a medical device; not for clinical use.