In an awake, hemodynamically stable patient with adequate oxygenation (SpO₂ ≥ 90 % on FiO₂ ≤ 0.4) who meets standard weaning criteria, how is pressure‑support ventilation used for weaning and what specific ventilator settings (pressure support level, PEEP, trigger sensitivity, cycling‑off criteria, rise time, FiO₂, alarm limits) should be applied?

Pressure Support Ventilation for Weaning: Mode Setup and Parameter Settings

For weaning in hemodynamically stable patients meeting readiness criteria, conduct spontaneous breathing trials using pressure support ventilation set at 5–8 cm H₂O with PEEP 5 cm H₂O, as this approach increases SBT success rates from 77% to 85% and extubation success from 69% to 75% compared to T-piece trials. 1, 2

Understanding Pressure Support Ventilation (PSV)

PSV is a pressure-assist mode that augments each spontaneous breath with a clinician-selected level of positive airway pressure. 3 The ventilator delivers flow to reach and maintain the set pressure level throughout inspiration, then cycles off when inspiratory flow decreases to a predetermined threshold (typically 25% of peak flow). 3

Key advantages during weaning:

• Reduces patient work of breathing while maintaining spontaneous respiratory drive 3, 4
• Improves patient comfort compared to unsupported breathing 3
• Normalizes tidal volumes in patients with rapid shallow breathing patterns 4
• Provides more balanced pressure-volume work compared to unassisted breathing 3

Specific Ventilator Parameter Settings

Pressure Support Level

• Initial SBT: 5–8 cm H₂O 1, 2
• This modest level overcomes endotracheal tube resistance without providing excessive support that masks weaning readiness 1
• For patients with reduced lung compliance (<0.06 L/cm H₂O), higher levels up to 20–30 cm H₂O may be used during earlier weaning phases, but the final SBT should still use 5–8 cm H₂O 5
• Avoid using SIMV mode for weaning, as it produces inferior outcomes compared to PSV-based approaches 6, 2

PEEP Setting

• Set PEEP at 5 cm H₂O during the SBT 1, 2
• For patients with severe oxygenation failure or high baseline PEEP requirements, ensure PEEP is ≤10 cm H₂O before initiating weaning attempts 7
• PEEP helps maintain alveolar recruitment and reduces work of breathing from intrinsic PEEP in obstructive disease 1

FiO₂ Target

• Maintain FiO₂ ≤0.40 (40%) during the SBT 1, 2
• Titrate to achieve SpO₂ 90–96% 1
• For patients with chronic hypercapnia, target SpO₂ 88–92% 1, 2
• Do not attempt weaning if PaO₂ <55 mmHg on FiO₂ ≥0.40, as this predicts high failure rates 7

Trigger Sensitivity

• Use flow triggering set at 1–3 L/min for optimal patient-ventilator synchrony 1
• Pressure triggering can be set at -0.5 to -2 cm H₂O if flow triggering is unavailable 1
• Proper trigger sensitivity is essential to minimize work of breathing and prevent patient-ventilator dyssynchrony 1

Cycling-Off Criteria (Expiratory Trigger)

• Set expiratory cycling at 25% of peak inspiratory flow (standard default on most ventilators) 3
• For patients with obstructive lung disease, consider increasing to 40% to prevent auto-PEEP 1
• For restrictive disease, 25% is appropriate 1

Rise Time (Pressurization Rate)

• Set rise time to 0.1–0.2 seconds for most patients 1
• Faster rise times (shorter duration) improve patient comfort in those with high respiratory drive 1
• Slower rise times may be needed in COPD patients to prevent overshoot and discomfort 1

Backup Rate

• Do not set a backup rate during PSV weaning trials, as this converts the mode to a hybrid that does not truly test spontaneous breathing capacity 6
• If backup ventilation is needed, the patient is not ready for weaning 1

Alarm Limit Settings

High Priority Alarms

• High respiratory rate: >35 breaths/min 2
• Low SpO₂: <90% 1, 2
• High heart rate: >140 bpm or sustained increase >20% from baseline 2
• Blood pressure: Systolic >180 mmHg or <90 mmHg 2
• Apnea alarm: 20 seconds (standard safety parameter)

Monitoring Parameters

• Continuously observe for accessory muscle use, abdominal paradox, or diaphoresis 2
• Monitor pressure-time and flow-time scalars for patient-ventilator synchrony 1
• Terminate the SBT immediately if any failure criteria are met 2

SBT Duration and Assessment

Trial Length

• Standard-risk patients: 30 minutes 2
• High-risk patients: 60–120 minutes 2
• Most SBT failures occur within the first 30 minutes 2

Rapid Shallow Breathing Index (RSBI)

• Measure after 30–60 minutes of spontaneous breathing 7
• RSBI ≤105 breaths/min/L indicates readiness to proceed 2, 7
• RSBI <80 breaths/min/L strongly predicts success (7.5-fold increased likelihood) 7
• RSBI >100 breaths/min/L strongly predicts failure 7

Common Pitfalls to Avoid

Setting pressure support too high: Using >8 cm H₂O during the final SBT may mask inadequate respiratory muscle strength and lead to extubation failure. 1

Premature weaning attempts: Do not initiate SBTs when PaO₂/FiO₂ ratio is <200 mmHg or PEEP requirements exceed 10 cm H₂O. 7

Ignoring hemodynamic instability: Patients requiring vasopressor support are not ready for weaning regardless of respiratory parameters. 2, 7

Prolonging failed trials: If failure criteria develop, immediately return to full ventilatory support rather than continuing the trial. 2

Using SIMV for weaning: SIMV produces the poorest weaning outcomes in randomized trials and should be avoided. 6, 2

Inadequate monitoring: Close observation during the first 1–2 hours is essential, as delayed recognition of failure increases reintubation risk. 1

Post-Extubation Management

• Standard-risk patients: Extubate to supplemental oxygen via face mask or nasal cannula, targeting SpO₂ 88–92% 2
• High-risk patients (age >65, cardiac failure, >1 failed SBT, weak cough): Consider prophylactic noninvasive ventilation immediately after extubation to reduce reintubation rates (from 21% to 4%) and ICU mortality 2