The answer is this: they try to set the patient up to fail before he is extubated, as opposed to extubating him and chancing that he will fail then.
Consider this example:
Say the Peak pressure for a patient is 20 and the static pressure is 15. The difference between the two is the resistance. Pressure Support, therefore, should be set to equal resistance, which in this case would be five.
If, in our attempt to wean the patient, we turn the pressure support down to zero, then, some experts contend, we are setting the patient up to fail. Therefore, pressure support should never be turned below resistance.
That was the old way of thinking. With our new protocol, we want to make sure we know a person is ready to be extubated. Therefore, we want to challenge them. We must give the patient every opportunity to fail before we extubate.
Before we move on, we must discuss failure criteria. How do you know if a patient is failing?
Weaning failure criteria:
- RR greater than 30 over 5 minutes duration
- BP greater than 20% of baseline
- HR greater than 20% above baseline
- SpO2 greater than 92%
- Pt. becomes anxious, diaphoretic, or other indications of respiratory distress
Our updated protocol, then, calls to reduce the PSV to the lowest value possible, without making the patient feel like he is breathing through a straw. Thus, with the very small ETTs, we will still maintain a minimum PSV.
That in mind, our new protocol is written this way:
Stage 1: Daily weaning screen.
The patient must meet the following criteria in order to move on to stage 2:
- Fio2 less than .40
- PEEP less than or =5
- HR greater than 40 or less than 120,
- SpO2 greater than 90%
- Systolic BP greater than 90
- No vasopressors
- No signs or respiratory distress
- Able to follow commands, adequate cough
- Secretions thin and minimal
- plateau pressure less than 30cwp (higher may indicate ARDS)
Of course, if patient does not meet any one of the above criteria, the patient is to remain on current settings, unless otherwise directed by the physician.
Stage 2: Place patient on CPAP and PSV according to ETT size.
If the ETT is 8.0 or larger, the CPAP should be set at 5, PS at 0. If the ETT size is 7.5 or smaller, the CPAP should be set at 5, PS at 5 to meet resistance.
The FiO2 should stay at the current setting.
Once a patient is on these settings for five minutes and has not failed, weaning parameters should be done. The idea is that if a patient fails here, he more than likely would have failed if he had been extubated, saving the patient from having to re-intubated.
So, weaning parameters are the next step.
I'm sure all us RTs should know these values like the backs of our hands, but I'll list acceptable weaning parameters here just to be cool:
- NIF greater than -20
- VC greater than 10 ml/kg ideal body weight (IBW)
- VT greater than 5ml/kg IBW
- RR less than30
- VE greater than5 or less than 15
- RSBI less than 100.
If the patient fails weaning parameters, we stop the weaning attempt and place patient on previous settings. If, on the other hand, the patient succeeds this stage, we move on to what we call a spontanioius breathing trial (SBT) for 30 minutes to 120 minutes.
The SBT is done at the formentioned CPAP and PSV settings based on ETT size. Thus, we give the patient every chance to fail as possible.
If the paitent fails, we stop the trial and return to previous vent settings and call the physician.
Stage 3: If the patient continues to meet weaning criteria, repeat weaning parameters, draw ABG if indicated, and call physician for order to extubate.
As you can see here, this is not a true ventilator protocol, but a ventilator extubation protocol. A true protocol would allow us RTs to adjust Fio2, VT, PEEP and RR. This will be the next protocol we try to whip up.
The following is included in our extubation protocol:
1. RT to wean FiO2 to maintain SpO2 of 92% (or as specified by physician).
2. Once FiO2 reduced to 60%, RT to wean PEEP to 5 (or as specified by physician) in increments of 2 CWP over ____to maintain SpO2 >92% (or as specified by physician).
3. RT to wean RR to ____ to maintain ETCO2 greater than____ or less than ____
The idea here is that ABGs will not need to be drawn on a regular basis, as the EtCO2 and SpO2 will be used to monitor the patients respiratory status.
The idea here is that weaning parameters should not be performed on a daily basis, which is especially frivolous when a patient is on a PEEP >8. With the new extubation protocol updates listed above, weaning parameters will only be completed if the patient meets weaning criteria.
The main purpose of this protocol is to get patients off the ventilator at the shortest interval possible without harming the patient.
Aside from benefiting the patient -- the most important benefit -- the protocol will save the hospital money, save the doctor from excessive pages from RNs and RTs, and improve the morale of us RTs as we are allowed to use the knowledge and experience.