SIMV is Not a Compulsory Weaning Mode
SIMV (Synchronized Intermittent Mandatory Ventilation) is not a compulsory weaning mode and is actually considered the most ineffective method for weaning patients from mechanical ventilation. 1
Evidence Against SIMV for Weaning
SIMV has been shown to be inferior to other weaning methods such as Pressure Support Ventilation (PSV) and T-piece trials according to the American Thoracic Society and European Respiratory Society guidelines 2
Randomized controlled trials have consistently reported the poorest weaning outcomes when using SIMV compared to other weaning techniques 3
When all causes for weaning failure were considered in comparative studies, SIMV had a significantly higher failure rate (42%) compared to PSV (23%) 4
Preferred Weaning Methods
Spontaneous Breathing Trials (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 approaches:
- Low-level pressure support ventilation (5-8 cmH₂O)
- T-piece breathing
- Low-level continuous positive airway pressure
- Flow-triggering with no pressure applied to the airway 3
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 2
Classification of Weaning Process
- Patients can be categorized into three groups based on the difficulty and duration of the weaning process:
- Simple weaning: patients who successfully pass the first SBT and are extubated on the first attempt (up to 70% of ICU patients)
- Difficult weaning: patients who require up to three SBTs or up to 7 days from the first SBT
- Prolonged weaning: patients who require more than three SBTs or >7 days of weaning 2
Proper Weaning Protocol
A 30-minute spontaneous breathing trial (SBT) should be used to assess suitability for extubation 5
Most SBT failures occur within the first 30 minutes of the trial, making this an efficient assessment period 2
A switch from controlled to assisted IMV should be made as soon as patient recovery allows, but this is different from using SIMV as a weaning mode 5
For patients who fail SBTs, NIV (non-invasive ventilation) may be considered as an intermediate step in the weaning process, which has shown better outcomes than prolonged invasive mechanical ventilation 6
Why SIMV is Problematic for Weaning
During pressure-triggered SIMV, patients show little adaptation to ventilator assistance, with similar inspiratory effort required for both mandatory and spontaneous breaths 7
This lack of respiratory muscle conditioning may contribute to SIMV's poor performance as a weaning method 7
The intermixing of assisted and spontaneous breaths in SIMV can lead to patient-ventilator asynchrony, which may increase work of breathing 7
In conclusion, current evidence strongly supports the use of SBTs and PSV for weaning rather than SIMV, which has been demonstrated to be less effective for liberating patients from mechanical ventilation.