Sunday, July 17, 2011

Switching from Pressure Control to Volume Control Ventilation

During patient ventilator transports one may have to switch from pressure control (PC-CMV) to volume control (VC-CMV) ventilation, because the available transport ventilator does not have PC-CMV. Another reason is the operator is unfamiliar with PC-CMV.

Here are the steps and additional considerations to safely switch the patient over.

1. Document original PC-CMV settings, measured values, and alarm settings.

2. Change the mode to VC-CMV. Note- one may consider using VC-IMV if the patient is adding spontaneous breaths. Rationale- newer generation ICU ventilators utilize a floating/active exhalation valve during pressure based modalities (PC-CMV, etc.) allowing for the patient to exhale at anytime during breath delivery, this is not available when using volume based modes. VC-IMV will allow more flexibility in regards to how the spontaneous breath terminates.

3. Respiratory Rate- use the same rate setting the patient was on with PC-CMV. Consider setting rate to the patient’s measured total respiratory rate, if deep sedation or paralytics will be used during transport. Rationale- if the patient is adding significant spontaneous breaths on the original settings (contributing to the total minute ventilation) then this will have to be matched. If the patient’s drive is decreased due to pharmaceuticals and the original minute ventilation is not met, this will create an acidosis.

4. Tidal Volume- Set the tidal volume to match the measured tidal volume the patient was receiving during PC-CMV. Considerations- the peak pressures may be higher when switching to VC-CMV with the same tidal volume, because most transport ventilators deliver flow using a constant/square waveform pattern. The operator may have to decrease the set tidal volume due to higher pressures and increase the set respiratory rate to make up for the loss in minute ventilation.

5. Flow Rate- Set the flow rate to generate an inspiratory time that matches the previous I-time setting during PC-CMV, or start at 45 lpm and titrate based on patient’s comfort level.

6. FiO2 & PEEP- Use the same settings that the patient was receiving during PC-CMV. Note- Some transport ventilators only allow for a FiO2 of 100% .