What are the different modes and indications for mechanical ventilation in various respiratory conditions, such as Acute Respiratory Distress Syndrome (ARDS) and Chronic Obstructive Pulmonary Disease (COPD)?

Mechanical Ventilation Modes and Indications by Respiratory Condition

Volume-Assist Control (AC): The Default Mode for Most Critically Ill Patients

Volume-assist control is the most commonly used mode (56% of cases) and should be your default choice for patients with ARDS and most other forms of acute respiratory failure. 1

Why Volume AC is Preferred:

• Guarantees minute ventilation regardless of changing lung mechanics, which is critical when respiratory drive is unreliable or absent 1
• Allows precise control of tidal volume and plateau pressure, the two parameters most strongly linked to mortality in ARDS 2, 3
• Simplifies lung-protective ventilation implementation by directly controlling the variables that matter most 4

Core Settings for Volume AC in ARDS:

• Tidal volume: 6 mL/kg predicted body weight (acceptable range 4-8 mL/kg PBW, but start at 6) 5, 2, 3
• Plateau pressure: <30 cmH₂O as an absolute ceiling 5, 2, 3
• PEEP titrated to severity: Higher PEEP (typically >10 cmH₂O) for moderate-to-severe ARDS (PaO₂/FiO₂ <200); lower PEEP for mild ARDS 2, 3
• Respiratory rate: 20-35 breaths/minute to maintain adequate ventilation 4
• Accept permissive hypercapnia with pH >7.20 rather than compromising lung protection 2

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SIMV with Pressure Support: Limited Role, Mainly for Weaning

SIMV with pressure support is used more commonly in patients with milder oxygenation deficits (PaO₂/FiO₂ 201-300) than in severe ARDS, suggesting its primary role is during the recovery/weaning phase rather than acute management. 1

When to Consider SIMV:

• Transitioning from full support to spontaneous breathing in patients who are improving 1
• Patients with preserved respiratory drive who can participate in their ventilation 1

Critical Limitation:

• Variable tidal volumes make lung-protective ventilation harder to guarantee, which is problematic in ARDS where every breath above 8 mL/kg PBW increases mortality risk 2, 3

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Pressure-Control Ventilation: Uncommon but Has Specific Indications

Pressure-control ventilation is used in only 10% of ARDS cases and should be reserved for specific situations where volume-control fails. 1

When Pressure-Control May Be Appropriate:

• Severe ventilator dyssynchrony despite optimization of volume AC settings 2
• Persistently high plateau pressures (approaching 30 cmH₂O) despite reducing tidal volume to 4 mL/kg PBW 2
• Need for deep sedation or neuromuscular blockade where guaranteed pressure limits are prioritized 2

Critical Caveat:

• You must monitor delivered tidal volumes closely because they will vary with changing lung compliance—if compliance improves, tidal volumes can drift dangerously high 4

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Mode Selection by Specific Condition

ARDS (PaO₂/FiO₂ <300):

Use volume-assist control as your primary mode. 1

Mandatory settings regardless of mode:

• Tidal volume 6 mL/kg PBW (never exceed 8 mL/kg PBW) 5, 2, 3
• Plateau pressure <30 cmH₂O 5, 2, 3
• Higher PEEP (>10 cmH₂O) for moderate-to-severe ARDS 2, 3
• Prone positioning ≥12-16 hours daily if PaO₂/FiO₂ <150 mmHg (this reduces mortality RR 0.74) 2, 3
• Neuromuscular blockade for up to 48 hours if PaO₂/FiO₂ <150 mmHg 2, 3

Severe Asthma Requiring Mechanical Ventilation:

Use volume-assist control with settings specifically modified to prevent auto-PEEP and breath stacking. 6

Critical differences from ARDS ventilation:

• Lower respiratory rate: 10-15 breaths/minute (not 20-35) to allow complete exhalation 6
• Prolonged expiratory time: I:E ratio 1:4 or 1:5 (not the standard 1:2) 6
• Higher inspiratory flow rate: 80-100 L/min to minimize inspiratory time 6
• Larger endotracheal tube: 8-9 mm to decrease airway resistance 6
• Tidal volume 6-8 mL/kg PBW 6
• Plateau pressure <30 cmH₂O 6
• Low PEEP: start at 5 cmH₂O (zero PEEP is not recommended) 6

If severe hypotension develops: Immediately disconnect from ventilator and press on chest wall to actively expel trapped air 6

Sepsis-Induced ARDS:

Use the same lung-protective strategy as non-septic ARDS—the underlying cause doesn't change the ventilation approach. 5

• Tidal volume 6 mL/kg PBW 5
• Plateau pressure ≤30 cmH₂O 5
• Higher PEEP for moderate-to-severe ARDS 5
• Prone positioning if PaO₂/FiO₂ <150 mmHg 5

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Modes to AVOID

High-Frequency Oscillatory Ventilation (HFOV):

Do not use HFOV in adult patients with ARDS—this is a strong recommendation based on evidence of harm. 5, 2, 3

Noninvasive Ventilation (NIV) in Established ARDS:

No recommendation can be made for NIV in sepsis-induced ARDS, meaning it should not be your primary strategy once ARDS is established. 5

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Common Pitfalls to Avoid

• Do not use higher tidal volumes even if plateau pressures seem acceptable—both parameters must be optimized simultaneously, and tidal volume >8 mL/kg PBW increases mortality regardless of plateau pressure 2, 3

• Do not prioritize normocapnia over lung protection—accept pH >7.20 with permissive hypercapnia rather than increasing tidal volumes or respiratory rate excessively 2

• Do not delay prone positioning in severe ARDS—mortality benefit requires early implementation for ≥12-16 hours daily 2, 3

• Do not use high respiratory rates in asthma—this causes dangerous auto-PEEP accumulation and hemodynamic collapse 6

• Do not use recruitment maneuvers routinely—these are associated with harm and should only be used selectively in severe refractory ARDS 2, 3