What are the primary types of weaning (withdrawal of ventilatory support)?

Primary Types of Weaning from Mechanical Ventilation

The primary types of weaning from mechanical ventilation include spontaneous breathing trials (SBTs) using T-piece or low-level pressure support, pressure support ventilation (PSV) with gradual reduction, and synchronized intermittent mandatory ventilation (SIMV) with gradual reduction of mandatory breaths. 1

Spontaneous Breathing Trials (SBTs)

• SBTs are the gold standard approach for assessing extubation readiness and should be performed daily in patients who meet readiness criteria 2
• SBTs can be conducted using several methods:
  • T-piece breathing (no pressure augmentation) 1, 3
  • Low-level continuous positive airway pressure (CPAP) 3
  • Low-level pressure support ventilation (5-8 cm H₂O) 4, 3
  • Flow-triggering with no pressure applied to the airway 1
• The American College of Chest Physicians/American Thoracic Society guidelines suggest that initial SBT be conducted with modest inspiratory pressure augmentation (5-8 cm H₂O) rather than T-piece 3
• SBTs typically last 30 minutes, with longer trials of 60-120 minutes recommended for patients at high risk of extubation failure 3
• Most SBT failures occur within the first 30 minutes of the trial 2, 3

Pressure Support Ventilation (PSV)

• With PSV weaning, the level of pressure support is gradually reduced over time, typically by 2-4 cm H₂O at least twice daily 5
• Initial pressure support is typically set at 18.0 ± 6.1 cm of water and then gradually reduced 5
• PSV has been shown to be more effective than SIMV for weaning patients from mechanical ventilation 5, 6
• PSV allows patients to control their own respiratory rate and tidal volume while receiving adjustable levels of support 1

Synchronized Intermittent Mandatory Ventilation (SIMV)

• With SIMV weaning, the mandatory rate setting on the ventilator is gradually reduced over time 1
• The ventilator rate is initially set at approximately 10.0 ± 2.2 breaths per minute and then decreased, if possible, at least twice a day, usually by 2-4 breaths per minute 5
• Randomized controlled trials have consistently reported the poorest weaning outcomes using SIMV compared to other methods 1, 5, 6
• The American Thoracic Society and European Respiratory Society state that SIMV is inferior to PSV and T-piece weaning 4

Comparison of Weaning Methods

• A landmark study by the Spanish Lung Failure Collaborative Group found that once-daily SBTs led to extubation about three times more quickly than SIMV and about twice as quickly as PSV 5
• SBTs conducted with pressure augmentation (CPAP) are more likely to be successful than T-piece trials, with higher rates of extubation success (75.4% vs 68.9%) 3
• For patients at high risk of extubation failure, T-piece trials may be more specific (though less sensitive) in identifying patients truly ready for extubation 3

Newer Approaches to Weaning

• Noninvasive positive pressure ventilation (NIV) after extubation is recommended for patients at high risk for extubation failure 4
• For patients with high risk of lung collapse (e.g., morbid obesity or after cardiac surgery), direct extubation from CPAP levels ≥10 cmH₂O has been used successfully 4
• Automatic tube compensation, mandatory minute ventilation, and adaptive support ventilation are newer ventilation methods, but their role in difficult or prolonged weaning remains to be established 7

Classification of Weaning

• Patients can be categorized into three groups based on the difficulty and duration of the weaning process 4, 6:
  • Simple weaning: patients who successfully pass the first SBT and are extubated on the first attempt (up to 70% of ICU patients) 4
  • Difficult weaning: patients who require up to three SBTs or up to 7 days from the first SBT to achieve successful weaning (approximately 15% of patients) 4
  • Prolonged weaning: patients who require more than three SBTs or >7 days of weaning after the first SBT (approximately 15% of patients) 4

Weaning Protocols and Assessment

• Daily assessment of readiness for weaning should be performed using standardized protocols 4, 2
• A successful SBT does not guarantee successful extubation - approximately 10% of patients who pass an SBT will still fail extubation 3
• Implementation of respiratory therapist- or nurse-driven protocols may improve weaning outcomes 8
• Weaning should be considered as early as possible to avoid complications associated with prolonged mechanical ventilation 6