Quote from DeLanaHarvickWannabe
I just need someone to explain to me, in layman's terms even, what the heck the different vent settings mean. (AC? PSV? PEEP? PIP? IDK my BFF Jill?)
One of the settings on a vent determines the size of breaths that will be delivered (tidal volume aka Vt). Tidal volumes can be achieved by telling the vent to deliver either
a set volume (volume control aka VC) or
a set pressure (pressure control aka PC).
When the vent delivers a breath to achieve a set volume
, the pressure required to deliver the breath can vary from breath to breath. This is the PIP (aka peak inspiratory pressure) - the vent's measurement of the pressure required to deliver the breath. Conditions that effect lung compliance, like need for suctioning, atelectasis, or pleural effusions (to name a few) influence how much pressure is required to deliver a set tidal volume.
When the vent delivers a breath to achieve a set pressure
, the PIP will be consistent from breath to breath, but the size of the breath (the tidal volume) will vary from breath to breath. This variation is also due to lung compliance. For example, conditions that decrease lung compliance will decrease the volume of the breath because the vent is set to stop delivering the breath once the set pressure has been achieved (regardless of how big or small the breath is).
AC - "Assist Control" mode. When AC mode is being used, the ventilator is set to deliver breaths (whether the set rate on the vent or a patient initiated breath above the set rate) to achieve either
a set tidal volume (volume control aka VC) or
a set pressure (pressure control aka PC). Breaths are relatively consistent from one to the next because even when the patient initiates a breath above the set vent rate, the vent will "take over" once the breath is initiated and deliver a breath that achieves either the set tidal volume or the set pressure.
SIMV - "Synchronized Intermittent Mandatory Ventilation" mode. In SIMV mode, like AC mode, the vent will deliver tidal volumes at either the set volume or the set pressure for the number of breaths that are SET on the vent. Any patient initiated breaths can be of whatever size the patient wishes - they can take little breaths, they can take large "sigh" breaths - whatever they want.
PSV - "Pressure Support". Pressure support is used when the vent is in a mode that allows the patient to take variable sized spontaneous breaths, like in SIMV mode. Pressure support is used like the name implies, to help 'support the pressure' required to take a breath. It is normally used to assist the patient to overcome all the extra work of breathing through all of the external apparatus required to use a ventilator - ETT, filters, and the like.
PEEP - "Positive End Expiratory Pressure" (you may hear this term used interchangeably with CPAP or "Continuous Positive Airway Pressure" - lets ignore the differences for now). This is the set pressure that the ventilator keeps in the lungs at the end of an exhaled breath. It is used at different amounts of pressure for a variety of reasons, but the goal is always to create a little "back pressure" in the lungs. You can easily experiment with this idea - make a loose fist with one of your hands, press your lips against the round end of your fist at your pointer finger and thumb and exhale through it. Now tighten your fist a bit and do the same. Feel the difference? This is creating different levels of back pressure in your lungs. This is the very reason that we teach patients with COPD (for example) to practice "pursed lip breathing" - to create a little back pressure in their own lungs.
A couple of the common goals of using PEEP on a ventilator are to prevent atelectasis (a little bit of back pressure can prevent floppy, fragile little alveolar air sacs from collapsing at the end of an exhalation), or to force pulmonary edema out of the airways and alveoli back into the capillaries. PEEP is also commonly used to improve oxygenation. Let me use an example of how that works - atmospheric oxygen pressures
are different at different elevations because it is under more or less pressure
in the environment - think of oxygen at the summit of Mt Everest vs Sea Level - the more atmospheric pressure oxygen is under, the more help it receives in diffusing into the capillaries. Using a vent and PEEP allows you to artificially change the "atmospheric pressure" inside the lungs - increasing the pressure helping oxygen to diffuse into the capillaries.
Just a little Vent 101 from your friendly neighborhood RT (who is transitioning to nursing). I benefit on a daily basis from trolling the boards and gleaning valuable insight and information from the contributors here. Hope I have finally been able to give something back, lol.