4000 cc is required per minute to maintain a CO2 level of 38 mmHg if production is 200 cc/min

Boyles Law

(760)(200)=(38)(V2)

Physiologic Dead space can go up to 50% 

Minute Ventilation of up to 8L/min can be required 

With FRC of 2500 cc and a source of oxygenation, apneic oxygenation can occur

Survival is limited by CO2 accumulation not hypoxia 

Atelectasis secondary to uneven flow distrbution and lack of sighing

Secretion retention

Increased Dead Space

Ventilatory improvement may be seen in patients with poor or abnormal lung function 

Spontaneous

Controlled Ventilation

Assisted Ventilation

IMV

Synchronized IMV

Airway Pressure Release Ventilation

Jet Ventilation 

Each breath is triggered by the patient

Difficult to applying PEEP since a negative inspiratory force is required to initiate breath

Provides a minimum number of breaths per minute 

Patient initiated breaths are not assisted

Airway Pressure Release Ventilation 

(APRV)

Continuous pressure is applied

Exhalation occurs by interruption of pressure 

Can result in a large discrepancy between preset TV and the TV actually delivered 

4-5 cc/cmH2O on average

In neonates this represents a large loss of tidal volume 

TV

MV

Inspiratory Flow Rate

Parameters can be stable or unstable in response to patient or circuit changes 

80-100 cc/kg/min

Usually Provided by TV: 8cc/kg; Rate= 12/min 

8-10 cc/kg

Constant throughout life 

Allows redistribution of gas in alveoli

Not needed in healthy lungs 

Sparated into control box and bellows assembly

Presently used vents may require both electrical and oxygen power

Integrates pneumatic and electrical sources 

Allows controls of many things

Rate

Minute Vol/Tidal Vol

I:E Ratio

Sigh

Alarm Settings

Manual Cycle 

Two separate Systems

Anesthetic gases are contained inside of bellows

Exterior of bellows is pressurized with the drive gas (O2)

Numbers on the ventilator act as a rough estimate of tidal volume 

1. Inspiratory cycle begins with Closure of "spill valve"

2. Bellows collapse driving anesthetic gases to pt

3. Expiratory cycle begins with discontinuation of pressure to bellow chamber and opening of vent valve, releiving pressure in chamber 

4. Exhalation fills the bellows with fresh gas flow

5. Bellows are full the ventilator relief valve opens venting excess gas to scavenger 

Use a piston design

Driven by an electric motor

Do not consume Oxygen

TV and Minute Ventilation are more accurately measured

Decouple fresh gas flow during inspiration 

Works by:

Volume monitoring with tidal volume adjustment

Diversion of gas during inspiration by decoupling valve 

V/Q ratio is altered

Dead space is increased

Venous Return is decreased 

Large quantities of Oxygen

As much as minute ventilation 

Drager AV-E

Piston-driven ventilators 

Uses the venturi system to entrain room air into the chamber (O2 =35%)

Bellows leak will entrain room air into the system

Uses a muffler system to vent driver gas

Pressure relief valve opens at 2.0 cmsH2O

Uses compressed O2 to drive bellows

Bellows not completely emptied

Pressure Relief valve opens at 2.5 cmsH2O

Settings controlled by microprocessor