🗝️ Key Points

- ❌ Don’t chase perfect numbers: Adequate and safe is often better than “perfect but harmful.”
- 💨 Oxygenation levers: Start with FiO₂ and PEEP, but remember MAP is the true driver.
- 🫁 Ventilation levers: Adjust RR and TV, tailored to underlying physiology.
- 🚫 Watch your obstructive patients: Sometimes less RR is more.

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📝 Introduction

Ventilator management can feel overwhelming—there are so many knobs to turn, numbers to watch, and changes to make. But before adjusting any settings, it’s crucial to understand why the patient is in distress in the first place, because the right strategy depends on the underlying cause. In this episode, we’ll walk through three different cases to see how the approach changes depending on the problem at hand.

️ The 4 Main Ventilator Settings

Tidal Volume (Vt) 🌬️
- Amount of air delivered with each breath
- Typically set based on ideal body weight (6–8 mL/kg for lung protection)
Respiratory Rate (RR) ⏱️
- Number of breaths delivered per minute
- Adjusted to control minute ventilation and manage CO₂
FiO₂ (Fraction of Inspired Oxygen) ⛽
- Percentage of oxygen delivered
- Adjusted to maintain adequate oxygenation (goal SpO₂ 92–96%, PaO₂ 55–80 mmHg).
PEEP (Positive End-Expiratory Pressure) 🎈
- Pressure maintained in the lungs at the end of exhalation to prevent alveolar collapse and improve oxygenation

🧮 Modes of Ventilation

AC/VC (Assist Control – Volume Control)
- How it Works: Delivers a set tidal volume with each breath (whether patient- or machine-triggered).
- When It’s Used / Pros: Most common initial mode; guarantees minute ventilation; good for patients with variable effort.
- Limitations / Cons: May cause patient–ventilator dyssynchrony if set volumes don’t match patient’s demand.
AC/PC (Assist Control – Pressure Control)
- How it Works: Delivers a set inspiratory pressure for each breath; tidal volume varies depending on lung compliance/resistance.
- When It’s Used / Pros: Useful in ARDS (lung-protective strategy), limits peak airway pressures.
- Limitations / Cons: Tidal volume not guaranteed; must closely monitor volumes and minute ventilation.
PRVC (Pressure-Regulated Volume Control)
- How it Works: Hybrid: set target tidal volume, ventilator adjusts inspiratory pressure breath-to-breath to achieve it (within limits).
- When It’s Used / Pros: Common default mode on newer vents; combines benefits of VC (guaranteed volume) + PC (pressure limitation).
- Limitations / Cons: Can increase pressures if compliance worsens.
SIMV (Synchronized Intermittent Mandatory Ventilation)
- How it Works: Delivers set breaths, but allows spontaneous patient breaths in between (without guaranteed volume).
- When It’s Used / Pros: Used for weaning; allows patient effort.
- Limitations / Cons: Risk of increased work of breathing if spontaneous breaths are inadequate.
PSV (Pressure Support Ventilation)
- How it Works: Every breath is patient-initiated; ventilator provides preset pressure support to overcome airway resistance.
- When It’s Used / Pros: Weaning trials; patients with intact drive who just need assistance.
- Limitations / Cons: Not a full-support mode; not for unstable patients without spontaneous drive.

♟️ Ventilation Strategies

Airway Protection
- Low GCS, seizure, stroke
- Loss of gag/cough reflex
- High aspiration risk (vomiting, GI bleed, poor mental status)
Hypoxemic Respiratory Failure
- Severe pneumonia
- ARDS
- Pulmonary edema
- Inhalation injury
Ventilatory (Hypercapnic) Failure / Increased Ventilation Demand
- Severe metabolic acidosis (DKA, sepsis, renal failure) → need high minute ventilation
- COPD, asthma (if decompensating)
- Neuromuscular weakness (myasthenia, Guillain–Barré, spinal cord injury)
Airway Obstruction / Anticipated Loss of Airway
- Tumor, anaphylaxis, angioedema
- Facial or airway trauma
- Pre-op / anticipated deterioration

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

👤 Show Notes

Priyanka Ramesh, MD

PGY 1 Internal Medicine Resident

Cape Fear Valley Internal Medicine Residency Program Fayetteville NC Aspiring Pulmonary Critical Care Fellow

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REBEL Core Cast 146.0–Ventilators Part 4: Setting up the Ventilator

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REBEL Core Cast 146.0–Ventilators Part 4: Setting up the Ventilator