Respiratory failure management

Resp Failure Types - The Gas Exchange Fail

• Type 1: Hypoxemic (↓O₂, ↔/↓CO₂)

  • Patho: V/Q mismatch or shunt. Gas exchange fails.
  • A-a Gradient: ↑ Elevated. Calculated as $PAO_2 - PaO_2$.
  • Causes: ARDS, pneumonia, pulmonary edema, PE.

• Type 2: Hypercapnic (↓O₂, ↑CO₂)

  • Patho: Alveolar hypoventilation. Pump/bellows fail.
  • A-a Gradient: Normal.
  • Causes: COPD, asthma, neuromuscular dz (GBS, MG), CNS depression.

⭐ The key differentiator is the A-a gradient. A high gradient points to a problem with the lung parenchyma itself (V/Q mismatch/shunt), characteristic of Type 1 failure.

Diagnostics - Spotting the Struggle

• Arterial Blood Gas (ABG): The cornerstone of diagnosis.
  • Type I (Hypoxemic): $PaO_2$ < 60 mmHg with normal/low $PaCO_2$.
  • Type II (Hypercapnic): $PaCO_2$ > 45 mmHg with or without hypoxemia.
• Chest X-Ray (CXR): Identifies underlying causes (e.g., pneumonia, ARDS, pulmonary edema).
• Key Labs: CBC, BMP, cardiac enzymes, BNP to rule out other causes.

⭐ Berlin Criteria for ARDS Severity: Assessed by the $PaO_2/FiO_2$ ratio.

• Mild: 201-300 mmHg
• Moderate: 101-200 mmHg
• Severe: ≤ 100 mmHg

O₂ & Ventilation - The Breathing Boost

• Goal: Maintain SpO₂ > 90% (or 88-92% in COPD) & adequate tissue oxygenation.
• Escalation of O₂ Delivery:
  • Nasal Cannula (1-6L) → Venturi Mask (precise FiO₂) → Non-rebreather (up to 100% FiO₂) → High-Flow Nasal Cannula (HFNC).
• Non-Invasive Ventilation (NIV): For alert, cooperative patients without aspiration risk.
  • CPAP: Continuous pressure. Used for cardiogenic pulmonary edema, OSA.
  • BiPAP: Inspiratory (IPAP) & Expiratory (EPAP) pressures. Ideal for COPD exacerbations & hypercapnic failure.
• Invasive Mechanical Ventilation (IMV): For airway protection, severe hypoxemia, or ventilatory failure (↑pCO₂).

⭐ The PaO₂/FiO₂ ratio is critical for ARDS staging. A P/F ratio ($PaO_2 / FiO_2$) < 300 on PEEP ≥ 5 cmH₂O indicates mild ARDS.

ARDS Protocol - Lung Protection Plan

• Goal: Minimize ventilator-induced lung injury (VILI).
• Core Strategy: Low Tidal Volume (LTV) Ventilation.
  • Tidal Volume (Vt): 4-8 mL/kg ideal body weight.
  • Plateau Pressure (Pplat): Keep < 30 cm H₂O.
  • Permissive Hypercapnia: Allow ↑PaCO₂ if pH remains > 7.25.
• Oxygenation:
  • Target PaO₂ 55-80 mmHg or SpO₂ 88-95%.
  • Use lowest possible FiO₂.
  • Titrate PEEP using ARDSNet protocol to improve oxygenation & recruit alveoli.

⭐ For moderate-to-severe ARDS (P/F ratio < 150), prone positioning for ≥ 12-16 hours/day is proven to reduce mortality.

High‑Yield Points - ⚡ Biggest Takeaways

• Hypoxemic failure (Type I) results from V/Q mismatch or shunt; treat with supplemental O₂ and PEEP.
• Hypercapnic failure (Type II) is from alveolar hypoventilation; it requires ventilatory support (NIV or MV).
• NIV is first-line for COPD exacerbations and cardiogenic pulmonary edema.
• Intubate for airway protection, severe hypoxemia, acidosis, or if NIV fails.
• In ARDS, use low tidal volume ventilation (6 mL/kg) to prevent barotrauma.
• Primary goals: ensure adequate oxygenation (PaO₂ > 60 mmHg) and ventilation (normalizing pH).