Newer Modes of Ventilation
Why Newer Modes Were Developed?
Traditional modes (VCV, PCV, SIMV) have limitations:
- Ventilator-induced lung injury (VILI)
- Patient-ventilator asynchrony
- Diaphragm disuse atrophy
- Poor adaptation to changing lung mechanics
1️⃣ Airway Pressure Release Ventilation (APRV)
🔹 Concept
- Prolonged high CPAP level (PHigh)
- Short release phase (PLow)
- Spontaneous breathing allowed throughout
🔹 Physiological Basis
- Maintains alveolar recruitment
- Improves oxygenation
- Reduces atelectrauma
- Allows spontaneous breathing → better V/Q matching
🔹 Settings
- PHigh ≈ plateau pressure
- Thigh = 4–6 sec
- PLow = 0–5 cmH₂O
- Tlow = 0.2–0.8 sec (auto-PEEP maintained)
🔹 Indications
- Moderate–severe ARDS
- Refractory hypoxemia
🔹 Advantages
- Improves oxygenation
- Reduces sedation requirement
- Better hemodynamics
🔹 Controversy
No definitive mortality benefit in large RCTs.
2️⃣ Proportional Assist Ventilation (PAV+)
🔹 Concept
Ventilator delivers pressure proportional to patient effort.
Pressure delivered = % support × (Elastic + Resistive load)
🔹 How It Works
- Estimates lung compliance & resistance continuously
- Provides assistance based on patient effort
- Patient controls tidal volume and timing
🔹 Benefits
- Excellent synchrony
- Prevents over-assistance
- Reduces diaphragm atrophy
🔹 Limitations
- Requires spontaneous effort
- Not for deeply sedated patients
3️⃣ Neurally Adjusted Ventilatory Assist (NAVA)
🔹 Concept
Uses diaphragm electrical activity (Edi signal) to trigger & cycle breaths.
🔹 Mechanism
- Special nasogastric catheter with electrodes
- Detects phrenic nerve activity
- Ventilator responds proportionally
🔹 Advantages
- Best synchrony available
- Works even with air leaks (useful in NIV)
- Prevents double triggering
🔹 Limitations
- Expensive
- Requires specific equipment
- Not useful if diaphragm paralysis
4️⃣ Adaptive Support Ventilation (ASV)
🔹 Concept
Closed-loop ventilation that automatically adjusts:
- Respiratory rate
- Tidal volume
- Inspiratory pressure
Based on target minute ventilation.
🔹 Uses Otis equation(Proposed by Arthur B. Otis ,1950)
Chooses RR and VT combination that minimizes work of breathing.
🔹 Benefits
- Auto-weaning
- Reduces clinician workload
- Prevents excessive VT
🔹 Clinical Use
- Postoperative ventilation
- Controlled to spontaneous transition
5️⃣ Pressure-Regulated Volume Control (PRVC)
🔹 Hybrid Mode
- Volume guaranteed
- Pressure adjusted breath-to-breath
🔹 Benefit
- Prevents high pressures
- Delivers set tidal volume
🔹 Limitation
May increase pressure in obstructive lung disease.
6️⃣ Intellivent-ASV
🔹 Advanced closed-loop system
Automatically adjusts:
- FiO₂
- PEEP
- Minute ventilation
Based on:
- SpO₂
- EtCO₂
Useful in prolonged ICU ventilation.
7️⃣ High-Frequency Oscillatory Ventilation (HFOV)
🔹 Concept
- Very high rates (3–15 Hz)
- Tiny tidal volumes (< dead space)
- Constant mean airway pressure
🔹 Mechanism of Gas Exchange
- Taylor dispersion
- Pendelluft
- Molecular diffusion
🔹 Status
No mortality benefit in adult ARDS trials.
Still used in neonates.
8️⃣ Extracorporeal CO₂ Removal (ECCO₂R)
🔹 Ultra-protective ventilation
Allows:
- VT 3–4 mL/kg
- Very low driving pressures
Used in:
- Severe ARDS
- Hypercapnic failure
Bridges between ventilation and ECMO.
9️⃣ Diaphragm-Protective Ventilation (Emerging Concept)
Modern philosophy:
Avoid:
- Over-assistance → diaphragm atrophy
- Under-assistance → fatigue
Tools:
- PAV
- NAVA
- Edi monitoring
- Transpulmonary pressure monitoring
🔟 Flow-Controlled Ventilation (FCV)
New experimental mode:
- Constant inspiratory AND expiratory flow
- Minimizes shear stress
- Improves gas distribution
Still under evaluation.