REBEL Core Cast 142.0–Ventilators Part 2: Simplifying Mechanical Ventilation – Most Common Ventilator Modes

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Sep 22, 2025

Dive into the complexities of mechanical ventilation with an exploration of key modes used in the ICU. Discover the significance of controlled, assisted, and supported breaths. Learn that no single mode guarantees better outcomes; comfort for the patient is crucial. Examine the ins and outs of popular modes such as Assist Control and Pressure Support, along with potential pitfalls like the SIMV's tendency to create dyssynchrony. Get equipped to match ventilator settings to patient needs, ensuring optimal care.

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INSIGHT

Comfort Trumps A Single 'Best' Mode

No single ventilator mode improves mortality or morbidity, so comfort and synchrony matter most.
Use the mode that matches the patient, not a presumed 'best' mode for everyone.

ADVICE

Understand Assist-Control Basics

Recognize 'assist-control' means breaths are either controlled or assisted and a set tidal volume is delivered.
Check whether your ventilator is AC-volume or AC-pressure to know if tidal volume or pressure is fixed.

INSIGHT

Pressure Modes Reveal Compliance Changes

In AC-pressure the delivered tidal volume will vary with lung compliance.
Tracking tidal volume on pressure modes tells you changes in compliance over time.

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🗝️ Key Points

💨 Start with Breath Types: Controlled, assisted, and supported breaths are the foundation of all modes.
🛌 Comfort Over “Best Mode”: No mode improves mortality — focus on patient synchrony and comfort.
Know the Big 5 Modes: AC: All controlled or assisted (volume or pressure). PS: Fully spontaneous, great for SBTs. PRVC: Pressure-delivered, volume-targeted hybrid. SIMV: Mixed mode, less favored in adults. VS: Spontaneous mode with adaptive pressure.
⚠️ Watch for Pitfalls: PRVC may under-ventilate in agitation. SIMV often causes dyssynchrony.
🎯 Bottom Line: Master mode mechanics and match the vent to the patient — not the other way around.

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📝 Introduction

Mechanical ventilation can feel overwhelming, especially when faced with a sea of ventilator modes and unfamiliar terminology. In Part 2 of the series, we go beyond breath types and delivery mechanics to explore the most used modes in the ICU. We will break down each one; explaining how it works, when to use it, and why the goal isn’t the “best mode” but the most comfortable one for the patient.

️ Ventilator Modes Explained

Assist Control (AC)

Commonly mislabeled as “volume control” or “pressure control.”
Two main types:
- AC Volume: Delivers a preset tidal volume with each breath, whether machine-initiated (controlled) or patient-initiated (assisted).
- AC Pressure: Delivers a preset pressure; tidal volume varies based on compliance.
All breaths are either controlled or assisted.

Pressure Support (PS)

All breaths are spontaneous initiated by the patient.
The ventilator provides a preset level of pressure support, like a resistance band during a pull-up.
No set rate, but a backup mode (often AC) activates during apnea.
Commonly used for spontaneous breathing trials (SBTs) to assess extubation readiness.
- Typical goal: Patient breathing comfortably with PS ~5 cmH₂O and reasonable rate.

Pressure Regulated Volume Control (PRVC)

Also called autoflow or adaptive pressure ventilation.
A hybrid mode: Pressure-delivered, volume-targeted.
Delivers breaths with a decelerating flow waveform, mimicking physiologic breathing.
Adjusts pressure breath-to-breath to meet a target tidal volume with minimal required pressure.
Safety feature: Pressure limit (e.g., 30–35 cm H₂O). If exceeded, volume delivery stops early.
Pitfall: In agitated patients, rapid breathing may trick the ventilator into reducing pressure, causing under-ventilation.

Synchronized Intermittent Mandatory Ventilation (SIMV)

Less common in adult ICU but still commonly used in pediatrics.
Delivers a set number of mandatory (controlled or assisted) breaths.
Allows spontaneous, pressure-supported breaths between mandatory ones.
Example: SIMV 10 = 10 guaranteed AC breaths; additional breaths are spontaneous + supported.
Why it’s less popular: Found to be less effective than daily SBTs for weaning and frequent dyssynchrony from not giving enough PS (PS should target at least 2/3 of the AC breath volumes) .

Volume Support (VS)

A newer, fully spontaneous mode (like PS + PRVC).
Patient initiates all breaths.
The ventilator automatically adjusts pressure support to achieve a target tidal volume.
Think of it as the spontaneous cousin of PRVC—adaptive and volume-driven.

🚨 Clinical Bottom Line

Understanding ventilator modes starts with knowing breath types, delivery mechanics, and clinical goals. When it comes to choosing the right mode:

Focus less on the “best” mode and more on patient comfort and synchrony.
Recognize the strengths, limitations, and pitfalls of each mode.
Stay tuned for future episodes that dive into ventilator troubleshooting and advanced respiratory strategies.

Post Peer Reviewed By: Marco Propersi, DO (Twitter/X: @Marco_propersi), and Mark Ramzy, DO (X: @MRamzyDO)

Show Notes By: Nicole Ebalo, DO

👤 Guest Contributors

Eric Acker, MD

Internal Medicine, Chief Resident,

Cape Fear Valley Medical Center, Fayetteville NC

Nicole Ebalo, DO