What initial ventilator mode and settings (tidal volume, plateau pressure, positive end‑expiratory pressure, FiO₂, respiratory rate, inspiratory:expiratory ratio, sedation) are recommended for an adult with acute hypoxic or hypercapnic respiratory failure, including acute respiratory distress syndrome?

Initial Ventilator Settings for Acute Respiratory Failure

Use volume-controlled Assist-Control (AC) ventilation with a tidal volume of 6 mL/kg predicted body weight, plateau pressure ≤30 cmH₂O, and higher PEEP (10-15 cmH₂O for moderate-severe ARDS) as your initial ventilatory strategy for adults with acute hypoxic respiratory failure or ARDS. 1

Mode Selection: Assist-Control vs. Other Modes

AC ventilation is strongly preferred over SIMV for moderate-to-severe ARDS because AC delivers consistent lung-protective tidal volumes on every breath, whereas SIMV permits unsupported spontaneous breaths that can produce variable and potentially injurious tidal volumes exceeding lung-protective limits. 1

• Volume-controlled and pressure-controlled ventilation are equivalent in terms of clinical outcomes, gas exchange, and respiratory mechanics when tidal volume and plateau pressure are kept constant 2, 3, 4
• The choice between volume-control and pressure-control is less important than adherence to lung-protective parameters 4
• Pressure-control may offer improved patient comfort in spontaneously breathing patients with high respiratory drive, but provides no advantage in deeply sedated patients 2

Specific Initial Settings

Tidal Volume

• Set tidal volume at 6 mL/kg predicted body weight (adjustable within 4-8 mL/kg range based on plateau pressure). 5, 1, 6
• This is a strong recommendation with high-quality evidence for ARDS 5

Plateau Pressure

• Maintain plateau pressure ≤30 cmH₂O as an absolute ceiling—this safety threshold supersedes all other pressure measurements. 5, 1, 6
• Measure plateau pressure with an end-inspiratory hold maneuver 1
• Do not rely on peak airway pressure as your safety metric; only plateau pressure accurately reflects alveolar distension and ventilator-induced lung injury risk. 1

Driving Pressure

• Calculate driving pressure (Plateau pressure - PEEP) and target ≤15 cmH₂O. 6

PEEP

• Use higher PEEP (typically 10-15 cmH₂O) over lower PEEP in moderate to severe ARDS. 5, 7
• This is a weak recommendation with moderate-quality evidence 5

FiO₂

• For hypercapnic respiratory failure: titrate oxygen to achieve SpO₂ 88-92%. 5
• For hypoxic respiratory failure/ARDS: titrate FiO₂ to maintain adequate oxygenation while minimizing oxygen toxicity, typically targeting SpO₂ 88-95%. 5

Respiratory Rate

• Use the minimum respiratory rate necessary to maintain acceptable pH with permissive hypercapnia. 6
• Start with 16-20 breaths/minute and adjust based on pH and PaCO₂ 6

Inspiratory:Expiratory Ratio

• Standard I:E ratio of 1:2 is appropriate for most patients 3
• Inverse ratio ventilation (I:E 2:1 or 3:1) offers no proven benefit over conventional ratios when total PEEP and tidal volume are kept constant. 3

Adjunctive Strategies for Severe ARDS

Prone Positioning

• Initiate prone positioning for >12 hours daily immediately when PaO₂/FiO₂ <150 mmHg—this is a strong recommendation with proven mortality benefit. 5, 1, 6, 7
• Do not delay prone positioning; early implementation is critical 1

Recruitment Maneuvers

• Perform recruitment maneuvers in moderate-to-severe ARDS (PaO₂/FiO₂ <200 mmHg) to reduce mortality (RR 0.81) and improve oxygenation. 5, 7
• Mandatory hemodynamic monitoring during recruitment maneuvers; do not perform in hypovolemic or hemodynamically unstable patients. 7

Neuromuscular Blockade

• Consider continuous neuromuscular blockade for ≤48 hours when PaO₂/FiO₂ <150 mmHg despite optimization. 5, 6

Mechanical Power

• Calculate mechanical power using: 0.098 × RR × Tidal Volume (L) × (PEEP + Driving Pressure). 6
• Target mechanical power <17 J/min, and definitely keep <22 J/min. 6

Sedation Strategy

• Sedation should be titrated to achieve ventilator synchrony and patient comfort while allowing for daily awakening trials. 5
• For NIV in hypercapnic failure: use sedation only with close monitoring; infused sedatives require HDU/ICU setting. 5
• Intravenous morphine 2.5-5 mg (± benzodiazepine) may improve NIV tolerance in agitated patients 5

Critical Pitfalls to Avoid

• Never use SIMV as the initial mode in moderate-to-severe ARDS—the risk of excessive tidal volumes violates core lung-protective principles. 1
• Do not delay intubation and invasive ventilation when NIV is failing in hypercapnic respiratory failure; worsening pH and respiratory rate indicate need for escalation. 5
• Avoid high-frequency oscillatory ventilation in ARDS—this is a strong recommendation against its use. 5
• Do not perform recruitment maneuvers in patients with focal ARDS patterns, as these patients have less recruitable lung and higher risk of overdistension. 7

Monitoring and Adjustment

• Reassess physiological parameters (pH, PaCO₂, respiratory rate, plateau pressure) within 1-2 hours of initiating ventilation. 5
• Worsening pH and respiratory rate predict failure and necessitate immediate management change: interface adjustment, ventilator setting modification, or intubation. 5
• Implement conservative fluid strategy once tissue perfusion is adequate 5