Intro

This chapter explores the fundamentals of ventilators, discussing various breath types and delivery methods. It aims to simplify mechanical ventilation for internal medicine residents by providing a structured approach to mastering the technology.

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🧭 REBEL Rundown

🗝️ Key Points

- 💨 Master the 3 Types of Breaths
  Control, Assist, and Spontaneous — know the difference before tackling ventilator modes.
- 📦 Breath Delivery: Volume vs. Pressure
  Volume-Targeted = fixed volume → monitor pressure
  📈 Pressure-Targeted = fixed pressure → monitor volume
- 🫁 Lung Compliance = Pressure-Volume Relationship
  Volume mode: ↑ pressure = ↓ compliance (stiff lungs)
  Pressure mode: ↓ tidal volume = ↓ compliance

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📝 Introduction

For many medical residents, the ICU can feel like stepping into a pressure cooker. At the heart of that stress often lies one intimidating machine: the ventilator. Rather than diving headfirst into complex ventilator modes, this episode lays a critical foundation by breaking down the basic building blocks of mechanical ventilation, something every clinician should master before moving on to more advanced concepts. Once you know the 3 types of breaths and how those breaths are delivered, you can more easily understand most of the mechanical ventilator modes.

🧮 The 3 Types of Breaths

To simplify things, we use a pull-up analogy to explain the types of ventilator breaths:

🫁 The 3 Types of Breaths…It's Like

😮‍💨 Breath Delivery: Volume vs. Pressure

Once you know the type of breath, the next key concept is how it’s delivered:
1. Volume-Targeted Delivery
- The ventilator delivers a fixed tidal volume (e.g., 400 mL) with each control or assist breath.
- What to monitor: Pressure. As lung compliance worsens, pressure increases.
- Risk: Barotrauma if the pressure becomes too high.
2. Pressure-Targeted Delivery
- The ventilator delivers air to a preset pressure (e.g., 15 cm H₂O).
- What to monitor: Tidal volume. As compliance drops, so does delivered volume.
- Adjustment: Modify pressure to maintain appropriate ventilation.

🧱 Putting It All Together: Lung Compliance

The relationship between pressure and volume is described by compliance:
- 📐 Compliance = Δ Volume / Δ Pressure
In volume mode:
- Rising pressure to achieve the same volume = decreased compliance (stiff)
- Decreasing pressure to achieve the same volume = increased compliance (loose)
In pressure mode:
- Dropping tidal volume at a constant pressure = decreased compliance (stiff)
- Rising tidal volume at a constant pressure = increased compliance (loose)