Ventilation in CVICU

by lpn2crna1day lpn2crna1day Member

Has 2 years experience.

Hello to all. I have a few questions regarding the ventilator assisted patient in CVICU. Took a crash course respiratory class but having trouble pulling some of it together. Can someone in the simplest terms desrcibe the difference between A/C and SIMV. Kinda getting confused. Am I right in thinking that on A/C the patient is being delivered a set tidal volume with every breath even when breathing over the vent and with SIMV the patient is only getting a set number of breaths with a set tidal volume? So their breaths over the vent can be at a lower tidal volume. Also is pressure support the same as SIMV? If someone is one PS 12/5 I get the 5 of PEEP part but just feel like I am getting lost somewhere. Still on orientation but I still feel the need for a better understanding sooner than later. Thanks!

turnforthenurse, MSN, NP

Specializes in ER, progressive care. Has 7 years experience. 3,364 Posts

Think of A/C (or ACV) as always assisting. The rate is set, but every episode of patient effort delivers a vent breath at a present tidal volume. For example, you f = 12. The patient's f won't fall below 12, but if the patient is breathing faster (say, 16 breaths/min) the vent will deliver those extra breaths. Basically, all breaths are vent assisted. The patient can hyperventilate on this mode (therefore decreasing CO2 levels).

Think of SIMV as sometimes assisting. This mode allows the patient to use his/her spontaneous effort to breathe. This is a weaning mode and is used to help build up the muscles of respiration. The vent will not initiate breaths on the patient's own effort. For example, your f = 10. Again, the rate will not fall below 10. When the patient makes an effort to breathe, it is their OWN effort - the vent does not deliver those extra breaths, unlike in A/C or ACV.

PS or PSV delivers a burst of pressure during inhalation. This is only used when the patient has the opportunity for spontaneous breathing (so they might be on SIMV mode). PS/PSV decreases WOB and assists in spontaneous TV. PS/PSV starts at 10 and is increased in increments of 5-10cm H2O.