CO2 absorber

Adjustable Pressure Limiting Valve (APL)

Inspiratory and Expiratory Unidirectional Valves

Reservoir Bag

Circuit Hoses

Fresh Gas Supply 

Converts CO₂ into CaCO₃ and H₂O

CO₂ + Ca(OH)₂--> CaCO₃ + H₂0

4-8 mesh in size

Poxed and irregular

Allows for increased contact of the absorber with gases

Necessary for reaction to occur

Moisture contant of soda lime 10-22%

Resistance to gas flow is very low because of the granule size and canister configuration

Resistance is about 10 cmH2O at 60L/m

Is caustic

Under normal use no dust enters the circuit

No prospective studies have demonstrated this

Felt in large part due to the extremely alkaline nature of the CO2 absorber 

Presently only approved anesthetic that reacts with CO2 absorber

Trichoethlyene and chloroform can also react to produce toxic gases 

Used an indicator dye

Weak base which is converted to salt as the pH falls

Salt has a violet color which indicates exhaustion of absorption capacity 

Approximately 20L/100 gms absorber 

Therefore a 1000 gm canister can absorb 200L of CO2

Averages about 12 L/hr

Canister will be completely  exhausted in 17 hrs 

Approximately 500cc of airspace

To keep airspace greater than tidal volume, the canisters should be changed when half exhausted 

Occurs to some degree with every canister

Most absorption occurs at the top 1/7 of active granules

Causes degradation of des and iso to carbon monoxide 

Most commonly seen on monday mornings

Not a problem with amsorb 

Used to vent excess gases to scavenger

set fully open during spontaneous ventilation

set fulled closed for patients on the vent

set to mid-range level for assisted ventilation 

Fully open exerts about 1 cmH2O of pressure 

Dic type valves that can be seen through clear cover

absence or malfunction of valve can cause significant rebreathing

15% of machines tested have some degree of valve malfunction 

Allows patients to draw from reservior during inspiration 

Results in large flow rates (500 cc TV inspired q 2 sec therefore 15L/m flow)

Serves as a shock absorber, limiting circuit pressures

Means to give positive pressure 

22 mm

Different from common gas outlet and scavenger

Large diameter offers very low resistance 

3 cc/cm H2O/meter of tubing 

 Only areas of bi-directional flow constitute dead space 

3-6 L/m

smaller high pressure tubing

Enter circuit prior to inspiratory valve

Combines with gas exiting CO2 absorber 

Humidification

Decreased anesthetic use

Decreased heat loss

Decreased OR pollution 

Many fitting, disconnections common (Y-Site)

Valves required

not fully disposable 

system heavy and bulky 

Fresh gas flow is at the bag attachment

APL is at the patient connector 

Very effective for negative pressure inspiration 

Exhalation of CO2 is selectively vented

Fresh gas is selectively dumped out the APL

Spontaneous Ventilation: 70-100 mL/kg/min

Controlled Ventilation: 100-300 mL/kg/min

Fresh gas flow is near the patient connector

APL is at bag

Bag is filled laregly by exhaled gases

Positive pressure vents exhaled gases

In negative inspiratory cycle, exhaled gases are drawn to patient 

Most effective for controlled ventilation 

Controlled Ventilation: 70-100 mL/kg/min 

Spontaneous Ventilaton: 200-300 mL/kg/min 

Maximum mass of water vapor which can be carried by a given volume of air (mg/L)

Strongly dependent on temperature

Warmer the gas, the more water that can be held

Amount present in a sample, as compared to the absolute humidity possible at the sample temperature 

Expressed as % 

Heat of vaporization of water is relatively high

Water evaporation in airways requires heat from body and is a source of heat loss in patients

Thickening of secretions

Reduction in surfactant activity

Reduction in ciliary function

Possible mucosal damage

Heat Loss

Using circle with absorbent granules with low flow

using HME 

< 1L/min

Provides 100% relative humidity at room temperature 

Heat and Moisture Exchanger

(HME)

Can't do more than return patient's exhaled water

Cant add heat or moisture

Less efficient with longer cases or higher flows

Easy, inexpensive, silent, and without risk of overheating 

Hydrophobi HME

Hygroscopic HME

Contain wool, foam, or paper like material coated with moisture-retaining chemcials

More effective in increasing humidity but less bacterial/viral filters 

Provide perfect conditions

100% RH at room temperature

However rarely used because of various problems 

Overhydration

Overheating (burns)

Higher flows (flow-over type) requirements

Melted circuits

Aspiration