Controversy "Mixing Volume with Pressure"

There is no doubt that using a volume control mode (SIMV volume control) with a pressure control mode (pressure support) is a little illogical: the type, nature and shape of the breaths are completely different. On the one hand the patient is expected to synchronize with a volume controlled breath of limited peak flow, and on the other they can take their own breath and control it almost completely.
Consequently, a pressure controlled SIMV mode has been developed for partially weaned patient. Most authorities agree that SIMV volume control is a poor weaning technique, and the patient is better off fully established on pressure support or assist-control (pressure or volume) if requiring ongoing ventilation. However, for most post operative patients, heavily sedated patients and those with little lung injury, the mode used is probably irrelevant, and it is much easier to wean a patient from SIMV than from VAC.
Further, a high percentage of intensive care units worldwide use SIMV + pressure support as their prime method of ventilation, and there is little evidence that this “mixed” mode is of any harm to the patient. My recommendation is that once a patient begins to breath spontaneously, there is no indication for mandatory breaths, and the patient should be switched over to pressure support ventilation alone: gradual weaning of IMV breaths in these circumstances is unnecessary.

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