Episode 23: Basic Ventilator Review with Dr. Scott Stephens

In this episode I welcome Dr. Scott Stephens, Pulmonary Critical Care Physician at Johns Hopkins to the show. Dr. Stephens and I discuss basic ventilator settings, how to appropriately ventilate patients with hypoxemic vs. hypercarbic respiratory failure and how to think about weaning patients off of the ventilator.

Outline by Brian Park: Outline

6 Replies to “Episode 23: Basic Ventilator Review with Dr. Scott Stephens”

  1. Great talk! And I certainly hope there will be more to come delving into more advance ventilator topics.

    One thing that I find confusing, is that when we set a ventilator to “volume control” in the OR, is this different from Assist Control in the ICU? I don’t know if this is ventilator or manufacturer specific, but in the OR, when I set a tidal volume and respiratory rate, any breath that the patient takes above the preset rate appears un-supported. Is that correct? Whereas volume control as it is referred to in the ICU ,will give the full set tidal volume anytime a patient triggers a breath?

    1. Stephen, great question which, as you know because you and I discussed this quite a bit offline, led to some in person investigation to figure out the answer. As it turns out, the older vents in some of our operating rooms here at Hopkins have a mode labeled PC and a mode labeled VC. But these are NOT assist control modes. These are actually IMV modes. Therefore, any additional breaths that the patient tries to take above the set number get no support at all. When we refer to volume control (VC) in the ICU we are actually referring to ACVC which is “assist control volume cycled”. These old vents say VC but are referring to volume IMV.

      Thanks,
      Jed

    1. Hi Megan,

      Thanks for the comment. I’m really glad you’re enjoying the podcast. I am definitely planning on a follow up with discussion of advanced vent settings in the future. Best of luck with your ongoing training and thanks for all you do out there everyday.

      Best,
      Jed

  2. Thanks for the podcast! One thing I can’t seem to wrap my head around is in regards to adjusting MV in hypercarbic respiratory failure. It was mentioned that in order to increase exhalation time one can reduce tidal volume so there is less gas to blow off, decrease RR to allow more time in between breaths, or increase inspiratory flow rate. This all makes sense, but it’s confusing to me how this can be true when increasing RR and TV also result in decreased CO2. Am I missing something?

    1. Hi Kate, good question.

      I think you are conflating two separate issues. First is the fact that patients with obstructive lung disease need more time to exhale. If they don’t have enough time they can start to air trap (aka auto-peep or dynamic hyperinflation), retaining more and more air in their lungs until they build up enough pressure to impede venous return and cause hypotension. If that is happening, you need to give them more time to exhale with the approaches you have mentioned. The second issue is hypercarbia. To breathe off more CO2 you have to increase minute ventilation and to do this you can either increase respiratory rate or tidal volume. It can be tricky, in patients with obstructive lung disease, because if you increase respiratory rate you have to be careful to make sure they aren’t air trapping. I hope that helps!

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