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simv vs AC

By Lawrence Simon posted 04-19-2011 08:58

  
I am tring to find out the volume difference from SIMV and AC.  I understand that in AC every breath assist or control have the same VT.  But in SIMV which breaths get the vent set VT and which get the volume that the pt draws?  Example:  if the vent is set at a rate of 10 and the pt only take 10 bpm are they all at the set volume or if the pt starts five of the 10 breaths does he get 5 at the set volume and 5 at the volume he draws?
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Mary Barrows
04-21-2011 15:49

I was going to drop a message, but after reading Ariel's...not anything more I could add! Good job!

Ariel Garnero
04-19-2011 12:54

There are espontaneous breaths "initiated and terminated" by the patient and there are mandatory breaths tha are either "initiated or terminated by the machine" We also have "Assissted breaths" that are a type of mandatory breaths that are "pt initiated" and finally "Supported" that are a type of espontaneous breaths that has a insp pressure higher than the P baseline.
I assume that you are talking about AC/VC and not AC/PC (AC by itself just says that breaths are either controlled or assisted, not which one is the controlled variable).
In AC you set the VT and that is what the pt gets...unless there is a leak or the Palarm is reached and the vent will cycle off as a protective measure.
SIMV (again I will asume you are talking about SIMV/VC and not SIMV/PC' altough u mention the set VT). In SIMV/VC or VC/SIMV you set the RR. The Pt can take more breaths on top of the mandatory or assisted ones but not less than them. Any breath on top of the set RR will be espontaneous or supported if u use PS... and the Vt will depend on the Pt's Effort, Ps level and Lung mechanics
If the RR is set 10 at SIMV/VC and the Pt RR is 10 they are all "mandatory breaths" and 5 of them "Assisted" (the ones he triggered).
Watch the grafics "Pressure/Time" and "Vol/Time" and you will see the difference.