4. Auto Adjusting Modes of Ventilation

What do we set in Mandatory Minute Ventilation?

• RR

• VT

• Volume breath type (ti, fixed flow waveform)

• PEEP

• FiO2

***The RR & VT = determine a minimum MV

When in MMV is the patient receiving PSV breathes?

when pts MV is higher than what is set

When in MMV is the patient given volume control breathes?

when pts MV fall below what is set

• to increase it above the set level

What does MMV guarantee if pts drive to breathe is erratic?

MV

What do we set the MV at?

Lower than the current spontaneous level

• but high enough to provide at least adequate ventilation

Example: if pt is breathing at a RR of 18 and VT approx 400ml what would I set the target MV at?

Current MV = RR x VT (18 × 0.4L) = 7.2

Set target MV @ approx 5L

• RR @ 12

• VT @ 400ml

What is the only vent that has MMV?

Evita - Drager

What are the negatives of MMV?

• pt defaults to VC type breath = can be uncomfortable

• pt able to maintain adequate MV even when tiring out (RR will increase as VT declnes)

  • so pts MV might still look okay but pt is starting to tire out

What is the difference between MMV & PC-PSV?

MMV= VC breath

PC-PSV= PC breath

What do we set in PC-PSV?

• RR

• Ventilating Pressure

• PEEP

• FiO2

When will the patient receive PSV supported breathes in PC-PSV?

When breathing above set RR

PC-PSV is the same as what mode on NIV?

S/T

• but PC-PSV is invasive

When will the patient receive pressure control (same set PS level) breathes in PC-PSV?

When RR drops below what is set

How are breathes cycled in PC-PSV?

By flow (Esens)

What is the only vent that uses PC-PSV?

Drager - Evita

What do we set the RR at for PC-PSV?

Well below awake RR

Ex) If awake RR 15-20 set back up @ 10

When will we use PC-PSV?

• can be used instead of PSV and will replicate it

  • used to provide back up RR for pts who may go apneic

What is the concern with PC-PSV?

When breathing spontaneously in PSV there are 2 pressure that result in ventilation

1. Pressure from ventilation (PS)

2. Pressure from patient (diaphragmatic contraction)

***we don’t know how much effort pt is adding to breath***

• when pt goes apneic and stops supplying their ventilatory force we don’t know what VT we will see

  • pt could hypoventilate

What is Automode function?

Switch between spontaneous breath type & control breath type

• based on if pt is triggering (PS)

• or going apneic (control)

When will pts get a supported breath in automode?

When ventilator sense pts effort - switches to spontaneous

When will a patient receive a control breath in automode?

when pt stops breathing

What ventilator is automode only on?

Servo

Each control mode is linked to a spontaneous mode, what are they?

1. VC—> VSV (volume supported ventilation)

2. PRVC —> VSV

3. PCV —> PSV

How do we prevent extended apneic spell in automode?

Trigger time out

What is the trigger time out function?

• longest period of time that a patient can be apneic before they are switched back to the control mode

• longest possible time to set is 12 seconds

• after switching to spontaneous mode the vent will slowly lengthen out time pt can be apneic to a max of that time

What patients do we use automode on?

• pts receiving bolus sedations

• waking up from surgery

• pts having apneic spells while sleeping

• better used on pts who are stable breathing on spontaneous mode already, rather than still on control ventilation

***when decreased LOC

Automode negatives

• modes are linked - can’t choose other

• if switching to PSV there is no guarantee of VT or MV while breathing spontaneously

  • pt may be hypoventilating

What is volume support function?

Pressure support targeted to a set VT

• we set VT not the driving pressure

• vent adjusts pressure (PS level) breath to breath to target the VT set

  • assess pts previous VT and increases or decreases PS for next breath

How can we trend support level in volume support?

Look at delta P (Ppeak - Peep)

When would we use volume support over PS?

to over ride current effort and take away work of breathing

• set VT slightly higher than current spontaneous level (extra 100ml)

• pt will get more VT than desired

• workload should decrease

What vents is volume support used on?

• Servo

• PB980

What was volume supoort initially designed for?

• as automatic weaning mode

• as pt disease state improved and muscle strength grew the pt would do more work and ventilator would use less pressure

Why does the volume support idea have a flaw?

• pt will always make least amount of effort since they want to be efficient and not waste calories

  • so the idea of helping to wean doesn’t work since they will ride the vent and use the extra pressure