Ventilator Management Strategies

Vent Modes & Settings - The Control Panel

• Core Modes:
  • Volume Control (VCV): Set $V_T$, pressure varies.
  • Pressure Control (PCV): Set pressure, $V_T$ varies.
  • Pressure Support (PSV): Patient-triggered, pressure-assisted breaths.
  • SIMV (VC or PC): Mandatory breaths + spontaneous breaths.
• Key Settings (Initial):
  • Tidal Volume ($V_T$): 6-8 mL/kg IBW (ARDS: 4-6 mL/kg).
  • Respiratory Rate (RR): 12-20/min.
  • PEEP: 5-10 cm $H_2O$.
  • $FiO_2$: Start 1.0, titrate to $SpO_2$ > 92-94% (or $PaO_2$ 60-80 mmHg).
  • I:E Ratio: 1:2 to 1:3.
  • Trigger: Flow or pressure.

⭐ In Volume Control Ventilation (VCV), tidal volume is guaranteed, but airway pressures vary; in Pressure Control Ventilation (PCV), pressure is set, but tidal volume varies with lung compliance and resistance.

ARDS & LPV - Gentle Breaths

⭐ The single most important ventilator strategy improving survival in ARDS is low tidal volume ventilation (6 mL/kg PBW, target Pplat ≤ 30 cmH2O).

• Core Goal: Minimize Ventilator-Induced Lung Injury (VILI) by reducing barotrauma & volutrauma.
• Key LPV Settings:
  • Tidal Volume (Vt): 6 mL/kg Predicted Body Weight (PBW). Use ARDSNet tables for PBW.
    • Reduce to 4 mL/kg if Pplat remains > 30 cmH2O.
  • Plateau Pressure (Pplat): Target ≤ 30 cmH2O.
  • PEEP: Optimize using ARDSNet PEEP/FiO2 table or decremental trial for best compliance/oxygenation.
  • Driving Pressure ($\Delta P = P_{plat} - PEEP$): Target < 15 cmH2O.
  • Permissive Hypercapnia: Accept PaCO2 ↑ (keep pH > 7.20-7.25) to maintain LPV.

Obstructive & NMD - Special Cases

Obstructive (Asthma, COPD):

• Goal: Prevent dynamic hyperinflation.
• Settings:
  • ↓ RR (8-12/min)
  • Vt 6-8 ml/kg PBW
  • ↑ Te (I:E 1:3-1:4)
  • Permissive hypercapnia (pH > 7.20)
  • Pplat < 30 cm H2O
• Monitor: Auto-PEEP.

Neuromuscular Disease (NMD):

• Goal: Support ventilation, airway protection.
• Settings:
  • Vt 6-8 ml/kg PBW
  • RR 12-16/min
  • PEEP 5 cm H2O
• Monitor: NIF/FVC, secretions.

⭐ In severe asthma/COPD exacerbations, the primary ventilator goal is to prevent dynamic hyperinflation by allowing adequate expiratory time (e.g., I:E 1:3 or 1:4), reducing set respiratory rate, and tolerating permissive hypercapnia.

Weaning & Complications - Path to Liberation

• Weaning Readiness Criteria:
  • Resolution/stability of acute illness; Hemodynamic stability (e.g., no/low dose vasopressors).
  • Adequate oxygenation: PaO₂/FiO₂ > 150-200 mmHg, PEEP ≤ 5-8 cmH₂O, FiO₂ ≤ 0.4-0.5.
  • Patient initiates spontaneous breaths; pH > 7.25; Afebrile.
• Spontaneous Breathing Trial (SBT) & Predictors:
  • SBT: 30-120 min (T-piece or low Pressure Support Ventilation ~5-7 cmH₂O).

  ⭐ The Rapid Shallow Breathing Index (RSBI = RR/TV in Liters) is a widely used predictor of weaning success, with a value < 105 breaths/min/L suggesting readiness for liberation from mechanical ventilation.

  • Other predictors: Max Inspiratory Pressure (MIP/NIF) < -20 to -30 cmH₂O; P0.1 (airway occlusion pressure) < 4-5 cmH₂O.
• Weaning Process:

• Key Complications:
  • Weaning Failure: Inability to pass SBT or sustain spontaneous breathing post-extubation.
  • Post-Extubation Stridor: Laryngeal edema. Manage: steroids, racemic epinephrine.
  • Ventilator-Induced Lung Injury (VILI): Barotrauma, Volutrauma, Atelectrauma.
  • Ventilator-Associated Pneumonia (VAP): New infection >48h post-intubation. 📌 VAP prevention bundle.
  • Diaphragmatic Dysfunction: Due to prolonged controlled ventilation/disuse.

High‑Yield Points - ⚡ Biggest Takeaways

• ARDSNet: Low TV (6 mL/kg PBW), Pplat <30 cm H2O limits VILI.
• Driving Pressure (Pplat - PEEP): Target <15 cm H2O for better survival.
• PEEP: Optimize oxygenation, prevent atelectrauma; titrate carefully.
• Permissive Hypercapnia: Acceptable in ARDS & asthma to reduce VILI.
• Weaning: SBT is key; RSBI <105 predicts success.
• NIV: Preferred for COPD exacerbations & cardiogenic pulmonary edema.
• Prone Positioning: For severe ARDS (P/F <150), improves oxygenation.