How to wean an intubated patient tolerating 40% Fraction of Inspired Oxygen (FiO2) in Assist-Control (AC) Volume Control (VC) mode?

Weaning Intubated Patients Tolerating 40% FiO2 in AC Volume Control Mode

For patients tolerating 40% FiO2 on AC volume control, proceed directly to a spontaneous breathing trial (SBT) using low-level pressure support (5-8 cm H₂O) rather than T-piece, as this approach has higher extubation success rates and is recommended by the American College of Chest Physicians/American Thoracic Society. 1

Pre-Weaning Assessment Criteria

Before initiating weaning, verify the patient meets these specific thresholds:

• Oxygenation adequacy: PaO2/FiO2 ratio ≥200 (with your patient at 40% FiO2, this means PaO2 should be ≥80 mmHg) 2, 1
• PEEP requirement: ≤5 cm H₂O 1
• Rapid shallow breathing index (RSBI): ≤105 breaths/min/L 1
• Airway protection: Intact cough reflex on suctioning 1
• Hemodynamic stability: No vasopressor infusions 1
• Mental status: No ongoing sedative infusions 1

Step-by-Step Weaning Protocol

1. Initial Spontaneous Breathing Trial

Conduct the SBT using pressure support ventilation at 5-8 cm H₂O rather than T-piece, as this method yields 75.4% extubation success versus 68.9% with T-piece 1. The American Thoracic Society/European Respiratory Society guidelines explicitly state that this modest pressure augmentation is superior to T-piece trials 1.

Set the following parameters for the SBT:

• Pressure support: 5-8 cm H₂O 1
• PEEP: ≤5 cm H₂O 3
• FiO2: Maintain at 40% or lower 3, 2
• Duration: 30-120 minutes (most failures occur within the first 30 minutes) 1

2. Monitoring During the SBT

Assess for SBT failure indicators continuously during the first 30 minutes (when most failures occur) 1:

• Respiratory rate >35 breaths/min or increasing trend
• SpO2 <90% 3
• Heart rate >140 bpm or sustained increase >20%
• Systolic blood pressure >180 mmHg or <90 mmHg
• Increased anxiety or diaphoresis
• Use of accessory muscles or abdominal paradox

Critical pitfall: Do not measure RSBI during the first minute of spontaneous breathing, as respiratory drive may still be suppressed; wait at least 30-60 minutes for accurate assessment 3.

3. Acid-Base Considerations

Check arterial blood gas before the SBT to identify metabolic alkalosis, which is a common but overlooked cause of weaning failure 2. The American Thoracic Society notes that metabolic alkalosis reduces central respiratory drive, creating an imbalance between respiratory load and muscle capability 2.

If bicarbonate >30 mmol/L with pH >7.45:

• Reduce or hold diuretics temporarily 2
• Administer normal saline for chloride repletion and volume restoration 2
• Delay weaning until bicarbonate normalizes, as alkalosis will impair spontaneous ventilation 2

4. Extubation Decision

If the patient tolerates the SBT for 30-120 minutes without failure indicators, proceed to extubation 1. However, recognize that approximately 10% of patients who pass an SBT will still fail extubation 1.

For standard-risk patients:

• Extubate directly to supplemental oxygen via face mask or nasal cannula
• Target SpO2 88-92% (or 94% if no history of CO2 retention) 3

For high-risk patients (obesity, cardiac surgery, baseline hypercapnia, or FVC <50% predicted):

• Consider extubation directly to noninvasive positive pressure ventilation (NIV) 1, 3
• Use CPAP ≥10 cm H₂O for patients at high risk of lung collapse 1
• This approach reduces reintubation rates and mortality in hypercapnic patients 1

5. Post-Extubation Management

Use supplemental oxygen cautiously, particularly in patients with chronic hypercapnia 3. The American College of Chest Physicians warns that oxygen therapy may correct hypoxemia without treating underlying hypoventilation or atelectasis and can impair central respiratory drive 3.

Monitor continuously for the first 24 hours:

• SpO2 targeting 88-92% (avoid >96% in COPD patients) 3
• Respiratory rate and work of breathing
• Arterial blood gases if clinical deterioration occurs 3

Alternative Approach: Direct Extubation to NIV

For patients with chronic respiratory disease (COPD, obesity hypoventilation) or those who marginally pass the SBT, consider systematic extubation to NIV rather than continuing invasive weaning 4. This approach reduces the duration of endotracheal mechanical ventilation from 7.69 days to 4.56 days without increasing weaning failure rates 4.

NIV settings post-extubation:

• IPAP: Start at 10-12 cm H₂O, titrate up to 15-20 cm H₂O if needed 3
• EPAP: 5-10 cm H₂O (higher EPAP may be needed in obese patients) 3
• FiO2: Titrate to maintain SpO2 88-92% 3

Common Pitfalls to Avoid

Do not use synchronized intermittent mandatory ventilation (SIMV) for weaning, as the American Thoracic Society and European Respiratory Society explicitly state it is inferior to pressure support and T-piece methods 1.

Avoid prolonged gradual weaning in AC mode by reducing respiratory rate or tidal volume incrementally. This approach lacks evidence and delays extubation. Instead, use the SBT protocol described above 1.

Do not overlook secretion management, as inadequate airway clearance is a common cause of extubation failure 3. Ensure the patient demonstrates effective cough and minimal secretions before extubation 1.