• 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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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.

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.

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

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