Pressure Control Specific settings: The Pressure Control and Inspiratory Time

When in a pressure control mode, instead of setting the tidal volume and flow of air directly, remember that we set the pressure applied to the lungs over a specified time that causes the lungs to inflate to a certain volume. All the same rules apply as with IBW and tidal volume. You will still measure your patient’s height and calculate their IBW and their tidal volume range, but instead of setting the tidal volume directly, you will set a pressure to be applied and then watch what volume you see in your lungs after about three breaths:

• Too high? Decrease the PC by 2 cmH₂0.
• Too low? Increase the PC by 2 cmH₂0 and assess.

A safe pressure control to start at is 14 cmH₂0. Even with a slightly higher PEEP, it will ensure your peak pressures are still well below 35 cmH₂0.

This change is very quick, and, within approximately a minute, you should be able to adjust the PC up or down to be approximately 8 ml/kg.

Note: Being off by approximately 20 ml is not an issue. You will never be exactly the same. Try to stay under the 8mls instead of over. If you increased the PC by 1 cm H₂0 and your tidal volumes go from below 8 ml/kg to above, then undo that change and leave your volumes just below your maximum. Remember 8 ml/kg is the upper limit, and we do not want our volumes to be above that.

The approach to setting your inspiratory time is very similar to the mentality with flow. A default Inspiratory time of 0.8-1.0 seconds works for most adult patients. A good rule of thumb is to use an Inspiratory time of 1.0 second. If your I:E is 1:1 (remember Chapter 4? If needed, go back and review), you can decrease your Itime by 0.1 seconds to see if you can ensure your patient has enough time to exhale. Insufficient exhalation time should not be an issue unless your patient is triggering a lot of breaths above your set respiratory rate. The only time the I:E would end up at 1:1 or inverse is with high set RR (or patient triggering more breaths). Sedation could be considered in this case; consult your physician or RRT if the default Itime of 0.8-1.0 seconds is causing issues, alarms, or an I:E that is 1:1 or inverse.

Default Itimes of 0.8-1.0 seconds should be fine for all your patients as long as the RR is less than 24bpm. If directed by a physician or RRT to increase the RR, the Itime may start to be adjusted to ensure the I:E stays greater than 1:1. For the purposes of this course, we are discussing overall ventilation strategies that will work for most patients. For difficult-to-ventilate patients, refer to your physician or RRT.