Memory Joggers: Vents for Dummies
You can only control so many variables:
1. Rate
2. Volume
3. FiO2
4. Mode (support method)
1. Rate
- Normal = 8-16/minute
- Commonly set at 12-15/min when starting vent
- Increase rate to "blow off (lower) CO2"
2. Volume
- Tidal volume (VT)
- Usual formula approx 7-10 mg/kg ideal body weight
- Err on the low side
- In ARDS, use lower VT
3. FiO
- = fraction of inspired O2
- Usually start at 100%
- Wean as soon as is reasonable (O2 toxicity)
4. Mode
a) AC = assist-control
- Machine delivers a set VT each time pt takes a breat
- If patient doesn't breathe at or more than the set rate, machine will initiate breaths
b) IMV = intermittent mandatory ventilation
- Pt breathes spontaneously, but machine delivers breaths at a pre-set rate/vol/pressure.
- NOT coordinated with pt's breaths
c) SIMV = synchronized IMV
- The IMV is synchronized with the pt's breaths/efforts
- Much more comfortable for the pt
d) Pressure Support
- Each pt breath effort is supported by a set amount of inspiration pressure
- VT not pre-set - determined by pt
- Rate not pre-set - determined by pt
Summary
Rate: usually 8-16/min, increase rate to blow of CO2
Vol: Approx 10 ml/kg ideal body weight; Avg size person approx 700 cc, small person approx 550-600 cc
Mode: Many times start with AC. SIMV also reasonable
FiO2: start at 100%; titrate down when can, usually don't try to titrate below 40% (if pt doesn't need even 40% FiO2, the pt may not really need the vent anyway)
Extras:
PEEP (positive end-expiratory pressure)
- Some intensivists always use a little PEEP, some don't
- Try it if having difficulty maintaining good PO2/O2 sats even though FiO2 is high and volume adequate, etc.
- Start with 5, can increase by 2-5 as needed
- Beware of barotrauma!
Vent Checklist
- Check CXR for ET tube placement
- Check ABG 15-30 min after starting vent or making big changes
- Get your vent management consult!
- Sedation as needed (prn benzos, versed/propofol drip, etc)
Becky Hoffman, November 2003 |
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