What is a Machine/Mandatory Breath on the Ventilator?
- RT Jaime
- Jul 8, 2022
- 2 min read
I've had people ask me this on multiple occasions and have had to explain it in the ICU many times. It's fine, that's what I do, I explain and I'm happy to do so!
So, on the ventilator there are two types of breaths. There are machine or mandatory breaths, and spontaneous breaths.
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Machine (AKA Mandatory) Breath
A machine breath is very much so controlled by the machine! Big surprise there. This means the machine controls the Inspiratory Time and how much volume and or pressure the patient is receiving. Machine breaths occur in Assist Control Modes and SIMV modes. They do not occur in Spontaneous breathing modes of ventilation.
The common misconception learners have is that if a patient is breathing over the set rate in assist control, that the breath must not be a machine delivered breath, but it in fact is. Yes, the patient can trigger more breaths than the set rate in an AC mode, however, the breath is still controlled for how much tidal volume is delivered and the inspiratory and expiratory time of the breath. It is still very much so controlled. This is what makes it different from a spontaneous breath, which I will get to in the next Blog Post!
In AC modes if a patient is taking huge tidal volume breaths on their own you may see a waveform that looks like this on the pressure waveform:
This happens because the patient is taking a large breath above their goal tidal volume so the machine delivers what looks like two separate breaths. This happens because like I said the machine has a set I-time and it automatically starts exhaling after reaching that I-time. This should not be too alarming, however keep an eye on possible autopeep and maybe hurry up and SBT/extubate them since they are breathing well above their set Vt, granted they meet extubation criteria.
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