Volutrauma and Low Tidal Volumes

Frank summarizes ARDSNet evidence for low tidal volumes (6 mL/kg IBW) to avoid volutrauma and how to calculate IBW.

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Episode notes

🧭 REBEL Rundown

💨 Peak vs. Plateau Pressures: PIP reflects total airway resistance and compliance, while Pplat isolates alveolar compliance—elevations in both suggest decreased lung compliance (e.g., ARDS, pulmonary edema, pneumothorax).
🧱 PEEP Protects Alveoli: Maintains alveolar recruitment and prevents collapse; typical range 5–8 cmH₂O, but higher levels may benefit moderate–severe ARDS.
️ Driving Pressure (ΔP = Pplat − PEEP): Lower ΔP reduces atelectrauma and improves outcomes; optimize by adjusting PEEP thoughtfully.
💥 Prevent VILI: Keep Pplat < 30 cmH₂O, use low tidal volumes (6 mL/kg IBW), and monitor for barotrauma, volutrauma, atelectrauma, and biotrauma.
📚 Evidence-Based Practice: ARDSNet and subsequent trials confirm that lung-protective ventilation—low Vt, limited pressures, and individualized PEEP—improves survival in ARDS.

This episode reviews essential ventilator pressures and how to interpret them during ICU rounds.

Peak Inspiratory Pressure (PIP)
- Definition: Total pressure required to deliver a breath.
- Reflects: Airway resistance + lung/chest wall compliance.
- Common Causes of ↑ PIP:
  - Mucus plugging
  - Biting the endotracheal tube
  - Kinked tubing or bronchospasm
Plateau Pressure (Pplat)
- Definition: Alveolar pressure measured after an inspiratory hold.
- Reflects: Lung compliance (stiffness of lung tissue).
- When Both PIP & Pplat Are Elevated:
  → Indicates poor compliance (e.g., ARDS, pulmonary edema, pneumothorax).
Positive End-Expiratory Pressure (PEEP)
- Definition: Pressure remaining in airways at end-expiration to prevent alveolar collapse.
- Typical Range: 5–8 cmH₂O but needs to titrated to meet patient requirements
- Notes:
  - Provides physiologic “glottic” PEEP in intubated patients.
  - Using high PEEP strategy shows mortality benefit only in moderate–severe ARDS in meta-analysis.
Driving Pressure (ΔP)
- Definition: ΔP = Pplat − PEEP.
- Reflects: Pressure needed to keep alveoli open during the respiratory cycle.
- Goal: Lower ΔP → less atelectrauma & improved outcomes.
- Optimize: Increase PEEP to reduce ΔP and alveolar cycling.

↑ PIP & ↑ Pplat
- Interpretation: ↓ Compliance
- Common Causes: ARDS, pulmonary edema, pleural effusion, pneumothorax
↑ PIP & Normal/Low Pplat
- Interpretation: ↑ Airway Resistance
- Common Causes: Mucus plug, bronchospasm, tube obstruction or biting

Barotrauma:
- Mechanism: Excessive airway pressure damages alveoli.
- Prevention: Keep Pplat < 30 cmH₂O.
Volutrauma:
- Mechanism: Overdistension from excessive tidal volumes.
- Prevention: Use low tidal volume ventilation (6 mL/kg ideal body weight).
- ARDSNet trial: 6 mL/kg → lower mortality compared to 12 mL/kg.
- Ideal Body Weight: Based on height and sex, not actual weight.
- Typical patient: Tidal Volume: 6–8 mL/kg IBW
- ARDS: Tidal Volume: 4–6 mL/kg IBW
Atelectrauma:
- Mechanism: Repeated opening/collapse of unstable alveoli.
- Prevention: Optimize PEEP to keep alveoli open and reduce driving pressure.
Biotrauma:
- Mechanism: Inflammatory cascade (↑ IL-6, TNF-α) from mechanical injury.
- Effect: Can trigger systemic inflammation & multiorgan dysfunction.
- Prevention: Minimize all other forms of VILI.