What are the newer ventilatory modes for adult patients and how should they be applied to improve patient‑ventilator synchrony and lung protection?

Newer Modes of Mechanical Ventilation

For adult patients requiring mechanical ventilation, prioritize lung-protective ventilation with low tidal volumes (4-8 ml/kg predicted body weight) and plateau pressures <30 cmH₂O as the foundation, while newer advanced modes like adaptive support ventilation (ASV), neurally adjusted ventilatory assist (NAVA), and proportional assist ventilation (PAV+) can improve patient-ventilator synchrony through closed-loop control systems, though their mortality benefit remains unproven. 1

Core Lung-Protective Strategy (Applies to All Modes)

The fundamental approach transcends specific ventilator modes. All patients with ARDS must receive:

• Tidal volumes: 4-8 ml/kg predicted body weight (strong recommendation) 1
• Plateau pressure: ≤30 cmH₂O (strong recommendation) 1
• Driving pressure (ΔP): <15 cmH₂O - values ≥15 cmH₂O are associated with increased mortality 2
• PEEP individualization: Higher PEEP for moderate-severe ARDS (conditional recommendation) 1

Critical Caveat on High-Frequency Oscillatory Ventilation

Avoid routine use of high-frequency oscillatory ventilation (HFOV) in moderate or severe ARDS - this carries a strong recommendation against its use based on high-quality evidence showing no benefit and potential harm 1.

Advanced Modes: Physiological Advantages

Newer modes offer specific advantages over traditional assist-control or pressure support ventilation by implementing closed-loop control systems that respond to patient demands 3, 4:

Dual Control Modes

• Volume-assured pressure support (VAPS) and volume support: Combine pressure-targeted breaths with guaranteed minimum tidal volume delivery
• Automatically adjust pressure to maintain target volume as lung mechanics change 4

Adaptive Support Ventilation (ASV)

• Uses mathematical models to minimize breathing power and inspiratory pressure 5
• Automatically adjusts tidal volume and respiratory rate based on patient's lung mechanics
• Expected tidal volumes: ~7.4 ml/kg in ARDS patients, maintaining lung-protective parameters 5
• Implements automated weaning protocols 3

Neurally Adjusted Ventilatory Assist (NAVA)

• Uses diaphragmatic electrical activity (Edi) to trigger and cycle breaths 6, 4
• Key advantage: Synchronizes ventilator support in both timing and magnitude with patient's neural respiratory drive
• Reduces patient-ventilator asynchrony by responding to actual respiratory effort rather than airway pressure changes 3
• Particularly useful when air leaks or auto-PEEP cause trigger failures in conventional modes

Proportional Assist Ventilation (PAV+)

• Delivers pressure proportional to patient's instantaneous effort 4
• Adjusts support breath-by-breath based on measured resistance and elastance
• Allows patient to control breathing pattern while receiving proportional assistance 3

Airway Pressure Release Ventilation (APRV)

• Maintains high continuous positive airway pressure with brief releases for CO₂ elimination 6, 4
• Allows spontaneous breathing at any point in the cycle
• Theoretical benefit: Maintains alveolar recruitment while permitting spontaneous ventilation
• Evidence for outcome improvement remains limited 4

Application Algorithm for Mode Selection

Start with conventional lung-protective ventilation (volume or pressure control with low tidal volumes) for all patients 1.

Consider advanced modes when:

1. Persistent patient-ventilator asynchrony despite optimizing conventional settings → Trial NAVA or PAV+ 3

2. Difficulty maintaining both adequate ventilation and lung protection → Consider ASV for automated optimization 5

3. Refractory hypoxemia in severe ARDS → Implement prone positioning >12 hours/day (strong recommendation) before considering APRV 1

4. Weaning challenges → ASV or adaptive modes with automated protocols 3

Monitoring Requirements

Regardless of mode selected, monitor:

• Driving pressure (plateau pressure minus PEEP) - most important predictor of VILI risk 2
• Respiratory drive and inspiratory effort - excessive spontaneous effort can cause patient self-inflicted lung injury 2
• Patient-ventilator synchrony - look for double-triggering, ineffective efforts, premature cycling 3
• SpO₂ and hemodynamics continuously, especially during recruitment maneuvers 7

Recruitment Maneuvers and PEEP

For moderate-severe ARDS, consider recruitment maneuvers (conditional recommendation, low confidence) 1:

• Use ventilator-driven maneuvers (preferred over manual bag) 7
• Vital capacity maneuver: 40 cmH₂O for 7-8 seconds in normal BMI; up to 50 cmH₂O for BMI >35 kg/m² 7
• Essential: Ensure hemodynamic stability before performing; monitor continuously for hypotension or desaturation 7
• Always follow with adequate PEEP - recruitment maneuvers without subsequent PEEP provide only transient benefit 7

PEEP Titration Strategy

After recruitment, individualize PEEP to:

• Maintain functional residual capacity without overdistension
• Achieve lowest driving pressure for desired tidal volume 7
• Target SpO₂ 92-96%, PaO₂ 60-100 mmHg (avoid both hypoxemia and hyperoxemia) 2

Evidence Quality Considerations

The 2017 ATS/ERS/SCCM guidelines provide strong recommendations with moderate confidence for low tidal volume ventilation and prone positioning in severe ARDS 1. However, newer advanced modes lack definitive outcome data - their benefits are primarily physiological (improved synchrony, reduced work of breathing) rather than proven mortality reduction 3, 2. Therefore, never sacrifice fundamental lung-protective principles (low tidal volumes, limited plateau pressure, appropriate PEEP) in favor of a sophisticated mode name.

The taxonomy of modes continues evolving with manufacturer-specific terminology creating confusion 8. Focus on understanding the control variables (pressure vs. volume), breath sequences (mandatory vs. assisted), and targeting schemes (set-point vs. adaptive) rather than proprietary names 9.