No, Do Not Switch to SIMV Mode
If your patient is tolerating pressure assist-control (PAC) ventilation well, you should continue with this mode rather than switching to SIMV. There is no evidence that SIMV offers any clinical advantage over assist-control ventilation, and modern evidence suggests assist-control modes are generally preferred for acute ventilatory support.
Why Continue with Assist-Control
The available evidence shows no meaningful differences in clinical outcomes between these modes:
Mortality and major outcomes are equivalent: Multiple studies comparing A/C and SIMV found no significant differences in mortality, duration of mechanical ventilation, length of hospital stay, or need for tracheostomy 1, 2.
SIMV may increase work of breathing: When ventilator support is reduced equivalently in both modes, SIMV causes larger increases in oxygen consumption (32.7% vs 15.7%), CO2 production (23% vs 12.5%), and measured energy expenditure (30.7% vs 15%) compared to pressure support ventilation 3. This suggests SIMV imposes greater metabolic demands on patients.
Respiratory pattern changes with SIMV: Studies show that SIMV leads to significantly decreased tidal volumes and increased respiratory rates compared to assist-control, which may be less desirable for maintaining adequate ventilation 4.
The Modern Approach to Ventilator Modes
Current guidelines describe SIMV primarily as a historical mode rather than a preferred strategy 5. The guideline literature emphasizes:
Assist-control provides full support for each breath: Whether patient-triggered or machine-delivered, every breath receives the same preset support, ensuring consistent ventilation 5.
SIMV was designed for weaning but is not optimal: While SIMV allows some spontaneous breaths between mandatory breaths, this does not translate to better outcomes and may actually prolong weaning 6.
When to Consider Mode Changes
You should only consider changing ventilator modes when:
The patient is ready for weaning: Transition to pressure support (not SIMV) when the patient demonstrates clinical stability, improved gas exchange, and ability to trigger breaths consistently 6, 7.
There is documented patient-ventilator asynchrony: If specific dyssynchrony issues arise that cannot be resolved by adjusting trigger sensitivity, rise time, or cycling criteria on the current mode 8.
Clinical deterioration occurs: If oxygenation or ventilation worsens despite optimization of current settings.
Common Pitfall to Avoid
Do not routinely switch modes as part of a "weaning strategy." The outdated practice of using SIMV to gradually reduce mandatory breath rates has been superseded by protocols using daily spontaneous breathing trials on pressure support or T-piece 6. When your patient is ready to wean, conduct spontaneous breathing trials rather than switching to SIMV.
Since your patient is tolerating PAC mode, optimize the current settings (PEEP, FiO2, pressure levels) rather than changing to a different mode without clear indication.