Selecting Ventilator Modes in Mechanical Ventilation

Questions prior to selection?

Indications, pathology, treatment goals, patient interface, location, duration, staff training

Noninvasive PPV

CPAP and BIPAP. Improves oxygenation and ventilation

Indicated for pts. that can spontaneously breathe, COPD exacerbations, hypoxemic respiratory failure, etc.

Invasive PPV

Full and partial ventilatory support.

Indicated for patients who can’t breathe on their own, protect their own airway, etc.

Includes mandatory, spontaneous, and assisted breaths.

Full Ventilatory Support (FVS)

Provides all the energy for alveolar ventilation and uses higher ventilator rates of 8 or > breaths/min while maintaining adequate tidal volumes.

Mode: Assist/Control with a pre-set volume or pressure

Always used initially for pts. in ARF to rest their ventilatory muscles.

Partial Ventilatory Support (PVS)

Patient must actively participate in ventilation to help maintain adequate alveolar ventilation.

Uses lower vent rates of <6 breaths/min

Modes used when trying to discontinue vent support: IMV, PS, MMV

Mandatory Breaths

Ventilator controls timing, tidal volume, and inspriatory pressure

Spontaneous Breaths

Pt. controls the timing and tidal volume

Based on pt. demand and pt’s lung characteristics

Assisted Breaths

Has characteristics of both mandatory and spontaneous.

All or part of the breath is generated by the ventilator

Is delivering a consistent Vt important?

Yes, optimizes ventilation and oxygenation

Why is limiting pressure important?

Prevents barotrauma on the pt.

Targeting Volume as the Controlled Variable

Volume = constant, pressure = based on lung characteristics

Advantages: Guaranteed specific volume delivery and volume of expired gas

Disadvantages: Evident when the lung condition worsens. High peak and alveolar pressures can cause overdistension which can dmg the lung

Asynchrony can occur with the pt. and ventilator if volume/flow is inadequate

Settings in Volume Control

Tidal Volume (Based on IBW), Rate, Trigger sensitivity, Flow rate (I-Time on some vents. Gas Pedal), PEEP

Targeting Pressure as the Controlled Variable

Pressure = Constant. Volume = dependent on lung characteristics.

Considered a lung protective strategy

More comfortable for the spontaneously breathing patient.

Advantages of Pressure-Controlled Ventilation

Allows a set MIP, set pressure reduces overdistension risk.

Flow pattern mimics natural breathing, improves synchrony, more time for gas distribution.

Maximum Inspiratory Pressure (MIP)

Set limit for pressure during inhalation.

Disadvantages of Pressure-Controlled Ventilation

Volume varies with the pt’s lung characteristics

Vt and Ve decrease if lung characteristics decrease

Clinicians may be less familiar with Pressure control

Settings in Pressure-Control

Inspiratory Pressure, inspiratory time (Or specific I:E), Pressure Rise Time, Rate, Trigger sensitivity, PEEP

Decelerating flow during pressure control

Pressure ventilation produces a descending waveform.

The vent starts gas flow (inspiration), building up pressure in the upper airway, which leads to a pressure gradient to the alveoli.

Flow decreases to prevent overdistension. (Slowly stopping at a stop sign).

What happens if you increase the set inspiratory pressure?

Increased Volume

What happens if you decrease the pressure gardient between the set inspiratory pressure and PEEP?

Decreased Volume

You have a IP of 20 cm H20 and a PEEP of 5 cm H20. If the PEEP increases to 8cm H20 what happens to the delivered Vt?

The delievered Vt decreases

Three breath delivery techniques

Continuous Mandatory Ventilation (CMV), Intermittent mechanical ventilation (IMV), Continuous spontaneous ventilation (CSV)

What is CMV?

(Mandatory)

Time- (“Controlled Ventilation” or Pt.-Triggered (Assist Control).

“Locking out” a patient by making the ventilator totally insensitive to pt. effort is rarely advisable.

Variations of CMV?

Volume-Targeted (VC-CMV)

Pressure Targeted (PC-CMV)

What is (IMV)?

(Assisted)

SIMV - (Synchronized IMV)

Pt. receives a set number of mandatory breaths.

Pt. can breathe spontaneously between the mandatory breaths.

Most vents can provide pressure support for spontaneous breaths to increase volume.

Developed as a weaning tool.

What is SIMV

(Synchronized IMV)

All mandatory breaths are synchronized to a pts. inspiratory effort.

Variations of assisted ventilation

Volume Targeted (AC-VC)

Pressure Targeted (AC-PC)

What is CSV?

(Spontaneous)

All breaths are spontaneous and through the ventilator circuit.

CPAP is helpful for improving oxygenation in pts. with refractory hypoxemia and a low FRC.

PSV provides a constant pressure during inspiration once it senses that the pt. makes an inspt effort. Must have consistent spont breath and pattern. Pt. triggered, pressure limited, flow cycled

Diffferences between CPAP and PSV

CPAP: Expiratory Support. Constant through breathing cycle. Requires full breathing effort. Used for OSA, oxygenation, and alveolar recruitment

PSV: Inspiratory support. Pressure only applied for inspiration. Effort required to trigger. Used to overcome airway resistance and wean from vent.

PSV Steps

1. Operator sets insp pressure, PEEP, flow cycle criteria, and sensitivity level.

2. Pt. controls rate, flow, and i-time.

3. Vt is determined by the pressure gradient, lung characteristics, and pt effort

Variations of CSV?

Pressure support ventilation (PSV)

Spontaneous (SPONT)

Continous positive airway pressure (CPAP)

Volume Targeted CMV (VC-CMV)

All breaths are mandatory. If assisted = AC/VC

Though to minimize WOB during mechanical ventilation. Pt’s actually have 33% - 50% more WOB on inspiration.

Pressure Controlled CMV (PC-CMV)

All breaths are mandatory. If assisted = AC/PC

Time or pt. triggered, pressure targeted, and time cycled. Ventilator provides a constant pressure to the pt. during inspiration.

Operator sets i-time, PIP, and RR.

Vt delivered is influenced my Co and Raw of the lungs, pt effort, and set pressure.

High Pressure Alarm

Set 10-15 cm H2O above inspiratory pressure in PC-CMV or average PIP reading in VC-CMV

Volume Control Recap

Ventilator controls flow, and controls volume indirectly and vice versa. Inspiratory flow causes volume and pressure to rise linearly. Inspiratory cycles off when a preset tidal volume is met

Pressure Control Recap

Airway pressure is constant during inspiration. Inspiratory flow decelerates towards zero after reaching a peak value, and volume rises.

Inspiration ends after a preset inspiration time.

If inspiratory time is long enough, lung pressure with equilibrate with airway pressure and insp flow will stop.

Pressure augmentation (Paug)

Provides pressure-limited ventilation with volume delivery targeted for every breath.

Volume-Assured Pressure Support (VAPS)

Another term for pressure augmentation in ventilation.

Pressure-Regulated Volume Control (PRVC)

Delivers pressure controlled breaths that are volume-targeted, pt or time triggered, and time cycled.

Similar to AVAPS or NIV

Volume support ventilation

Basically, pressure support with a volume target

Mandatory Minute Ventilation (MMV)

Ventilator provides whaterver part of the minuet ventilation that the pt. is unable to produce, by increasing RR or preset pressure.

Used to wean pt. Alarms must be set appropriately

Airway Pressure-Release Ventilation (APRV)

Two pressure levels for oxygenation and CO₂ removal. Used for ARDS pts. to improve oxygenation and prevent lung injury

Provides P High (Distend Alveoli) and P Low (Allows exhlation and CO2 removal)

Allows spontaneous breathing at any time to improve pt comfort.

Neurally Adjusted Ventilatory Assist (NAVA)

Relies on pt neurological control of mechanical vent. Measures diaphragmatic EMG signal to control gas delivery.

Uses nasogastric tube with specialized sensors from diaphragm electrical activity to control timing and pressure.