Phases of a Breath and Ventilatory Phase Variables

Vocabulary flashcards covering the phases of a complete breath, ventilatory phase variables (trigger, limit, cycle, baseline), cycling mechanisms, and expiratory maneuvers based on mechanical ventilation lecture slides.

Four Phases of a Complete Ventilatory Cycle

The four sequential phases of mechanical breath delivery: 1. Initiation of inspiration, 2. Inspiration, 3. End of inspiration, and 4. Expiration.

Phase Variables

Parameters used by a mechanical ventilator to initiate, control, limit, or end each phase of ventilation.

Trigger Variable

The phase variable that initiates inspiration, transitioning the ventilator cycle from expiration to inspiration (E to I).

Limit Variable

A phase variable (pressure, volume, flow, or time) that reaches and holds a maximum preset value during inspiration without terminating the inspiratory phase.

Cycle Variable

The phase variable that terminates the inspiratory phase and initiates exhalation (I to E).

Baseline Variable

The pressure variable maintained throughout the expiratory phase relative to atmospheric pressure, usually defined at end-exhalation.

Time Triggering

A ventilator-initiated trigger mechanism where a breath is automatically delivered at set time intervals determined by a set respiratory rate (e.g., set rate of $20$ triggers a breath every $3$ seconds).

Pressure Triggering

A patient-trigger mechanism where patient inspiratory effort creates a drop in circuit pressure below baseline (typically set between $0.5$ and $2\text{ cmH}_2\text{O}$) to initiate inspiration.

Flow Triggering

A patient-trigger mechanism using a continuous bias flow where patient effort reduces flow returning to the exhalation valve (typically set $1\text{--}3\text{ lpm}$ below baseline) to initiate inspiration.

Neurally Adjusted Ventilatory Assist (NAVA)

A mode of ventilation that detects electrical activity (neural impulses) from the diaphragm using an esophageal catheter to trigger a breath.

Pressure Limiting

An inspiratory control method in pressure-control (PC) ventilation where pressure rises to a preset value and does not exceed it during inspiration, while volume and flow vary with lung mechanics.

Maximum Safety Pressure

A protective high-pressure alarm setting, typically set $10\text{ cmH}_2\text{O}$ above average peak inspiratory pressure (PIP), that ends inspiration immediately if reached to prevent lung injury.

Volume Limiting

An inspiratory control method in volume-control (VC) ventilation where a preset volume and flow pattern are delivered constantly, causing pressure to vary based on lung mechanics.

Flow Limiting

An inspiratory limiting mechanism where delivered flow reaches a maximum set value without exceeding it before the end of inspiration.

Pressure Cycling

A cycling mechanism where gas flow stops and inspiration ends as soon as a preset target pressure level is reached.

Volume Cycling

A cycling mechanism where inspiration ends after a predetermined preset volume of gas is expelled through the output control valve.

Flow Cycling

A cycling mechanism, commonly used in pressure support (PS) ventilation, where inspiration ends when inspiratory flow decelerates to a set threshold percentage of peak flow.

Time Cycling

A cycling mechanism where exhalation begins automatically after a preselected inspiratory time ($T_I$) has elapsed.

Inflation Hold (Inspiratory Pause)

A maneuver that keeps the expiratory valve closed at end-inspiration to hold gas in the lungs, increasing inspiratory time ($T_I$) and allowing measurement of plateau pressure.

Positive End-Expiratory Pressure (PEEP)

An expiratory baseline pressure maintained above atmospheric pressure by impeding exhalation flow, which increases functional residual capacity (FRC).

Zero End-Expiratory Pressure (ZEEP)

An expiratory baseline setting where airway pressure at end-exhalation equals atmospheric pressure ($0\text{ cmH}_2\text{O}$).

Expiratory Hold (End-Expiratory Pause)

A maneuver performed during exhalation to close the inspiratory and expiratory valves, used to measure intrinsic PEEP ($\text{PEEPi}$) or auto-PEEP.

Ventilatory Cycle Scalar Waveform Labels

A: Beginning of Inspiration, B: Inspiration, C: End of Inspiration, D: Beginning of Exhalation, E: Exhalation, F: End of Exhalation.