What are the different modes of ventilation and their uses?

Mechanical Ventilation Modes and Their Clinical Applications

Primary Ventilation Modes

The selection of ventilation mode should be guided by the underlying pathophysiology, disease severity, and patient respiratory drive, with no single mode demonstrating superiority across all conditions. 1

Volume-Controlled Ventilation (VCV)

• Delivers a preset tidal volume with resulting pressure determined by lung compliance and airway resistance 1, 2
• Primary use: Patients requiring guaranteed minute ventilation, particularly those with obesity (associated with lower peak airway pressures) 3
• Target: 6-8 ml/kg ideal body weight to minimize ventilator-induced lung injury 3
• Advantage: Ensures consistent tidal volume delivery regardless of changing lung mechanics 2
• Disadvantage: Risk of excessive airway pressures if compliance worsens 1

Pressure-Controlled Ventilation (PCV)

• Delivers a preset inspiratory pressure with resulting tidal volume dependent on lung compliance and resistance 1, 2
• Primary use: Patients at risk for barotrauma or with poor lung compliance 1
• Advantage: Limits peak airway pressures, potentially reducing ventilator-induced lung injury 2
• Disadvantage: Tidal volume varies with changes in respiratory mechanics 1

Assist-Control Ventilation (ACV)

• Guarantees a minimum respiratory rate while allowing patient-triggered breaths that receive full ventilator support 1, 2
• Primary use: Patients with variable respiratory drive, particularly for prolonged ventilation and nighttime use 3
• Key advantage: Prevents central apneas during sleep due to backup rate, improving sleep quality compared to pressure support 1, 3
• Critical setting: Must adjust expiratory time carefully—long expiratory times create long "lock-out" periods causing poor tolerance 1, 2
• Synchronization feature: Patient-triggered breaths delay the next mandatory breath (SIMV mode) 1

Pressure Support Ventilation (PSV)

• Patient triggers both inspiration and expiration, determining respiratory rate and timing 1, 3
• Primary use: Weaning patients with adequate respiratory drive 3
• Critical adjustment: Flow cycling sensitivity and rise time must be optimized to achieve appropriate inspiratory time 1
• Major pitfall: Excessive support causes hyperventilation, hypocapnia below apneic threshold, and central apneas—especially problematic during sleep and in heart failure patients 1, 3
• Safety feature: Most devices include backup rate of 6-8 breaths/minute if patient effort ceases 1

Advanced and Specialized Modes

Proportional Assist Ventilation (PAV)

• Delivers pressure proportional to patient effort based on respiratory mechanics 1
• Primary use: Improving patient-ventilator synchrony and potentially sleep quality 1
• Evidence: Reduces asynchrony and may increase slow-wave and REM sleep compared to PSV 1

Neurally Adjusted Ventilatory Assist (NAVA)

• Delivers pressure proportional to diaphragmatic electrical activity 1
• Primary use: Optimizing patient-ventilator interaction in patients with significant asynchrony 1
• Advantage: Directly responds to neural respiratory drive 1

High-Frequency Oscillatory Ventilation (HFOV)

• May be considered when conventional ventilation fails using open lung strategy 1
• Pediatric consideration: Can be used judiciously in obstructive airway disease and cardiac patients, including Fontan circulation 1
• Critical contraindication: Should NOT be used in obstructive airway disease due to dynamic hyperinflation risk 1
• Important caveat: No mortality benefit demonstrated in acute hypoxemic respiratory failure; some studies suggest increased mortality 1
• Cardiac patients: Use with particular caution in passive pulmonary blood flow or right ventricular dysfunction 1

Airway Pressure Release Ventilation (APRV)

• Insufficient data to recommend for routine use 1
• Theoretical benefit: May provide lung-protective ventilation in refractory hypoxemia 4

Non-Invasive Ventilation Approaches

Continuous Positive Airway Pressure (CPAP)

• Primary mechanism: Increases mean airway pressure, recruits collapsed alveoli, and offsets intrinsic PEEP 1
• Primary use: Correcting hypoxemia in mild-to-moderate respiratory failure 1
• Specific indications: Initial support in restrictive disease, mixed disease, and cardiorespiratory failure 1
• COPD benefit: Reduces work of breathing by offsetting intrinsic PEEP, potentially lowering PaCO2 1
• Important limitation: Not considered true respiratory support—mainly for oxygenation 1

Non-Invasive Ventilation (NIV)

• Can be considered before intubation in obstructive airway disease, restrictive disease, mild-to-moderate PARDS, or cardiorespiratory failure 1
• Critical timing: Success must be assessed within 1 hour by monitoring heart rate, respiratory rate, SpO2/FiO2, pH, consciousness level, and organ failure 1
• Absolute principle: Should NOT delay intubation when failing 1
• Interface selection: Use interface with least leakage—full face mask, oral-nasal mask, or helmet depending on local experience 1
• Contraindication: Avoid in severe ARDS (adult data shows increased adverse outcomes) 1

High-Flow Nasal Cannula (HFNC)

• May reduce work of breathing but no outcome data showing superiority over other interventions 1
• Use: Consider as initial support in mild disease 1

Critical Ventilator Settings and Monitoring

Pressure Limits

• Plateau pressure ≤28 cmH2O in most conditions 1
• May accept 29-32 cmH2O if chest wall elastance increased (restrictive disease, mixed disease) 1
• Cuff pressure ≤20 cmH2O for cuffed endotracheal tubes 1

Oxygenation Targets

• Healthy lungs: SpO2 ≥95% on room air 1
• General ICU: Keep SpO2 ≤97% 1
• PARDS with PEEP <10 cmH2O: SpO2 92-97% 1
• PARDS with PEEP ≥10 cmH2O: SpO2 88-92% 1
• Prolonged ventilation: Maintain SpO2 88-94% to avoid hyperoxia 3

Ventilation Targets

• Healthy lungs: PaCO2 35-45 mmHg 1
• Acute pulmonary/non-pulmonary disease: Accept higher PaCO2 unless contraindicated 1
• Target pH >7.20 in most conditions 1
• Pulmonary hypertension: Target normal pH 1

Essential Monitoring Parameters

• Measure: Peak inspiratory pressure, plateau pressure, mean airway pressure, PEEP 1
• Consider measuring: Transpulmonary pressure, dynamic compliance, intrinsic PEEP 1
• Monitor continuously: Pressure-time and flow-time scalars 1

Practical Implementation Strategies

Mode Selection Algorithm

1. Assess respiratory drive: Absent/minimal → CMV or ACV; Present → PSV or ACV 1, 2
2. Evaluate disease severity: Mild → Consider NIV/CPAP; Moderate-to-severe → Invasive ventilation 1
3. Consider pathophysiology: Obstructive → Longer expiratory time; Restrictive → Higher pressures may be needed 1
4. For prolonged ventilation: Use ACV at night to prevent central apneas 3
5. For weaning: PSV with carefully adjusted support to prevent hyperventilation 1, 3

Common Pitfalls to Avoid

• Terminology confusion: Ventilator manufacturers use different names for identical modes 1, 2
• Excessive PSV support: Causes hyperventilation and central apneas, particularly during sleep 1, 3
• Delayed intubation with NIV: Must assess success within 1 hour and intubate promptly if failing 1
• Inappropriate HFOV use: Contraindicated in obstructive disease due to air trapping 1
• Inadequate expiratory time: Ensure I:E ratio of 1:2 or 1:3 to prevent air trapping 3

Weaning Considerations

• Start weaning as soon as possible 1
• Perform daily extubation readiness testing 1
• Consider NIV for neuromuscular patients post-extubation 1
• Use corticosteroids in patients at increased risk for post-extubation stridor 1

Supportive Measures

• Always use humidification 1
• Maintain head of bed elevated 30-45° 1
• Minimize circuit dead space 1
• Use double-limb circuits for invasive ventilation 1
• Avoid routine hand ventilation unless specifically indicated 1