A). When the carrier gas is quickly switched to 100% nitrous oxide

(B). the halothane concentration decreases to 3% within 8 to 10 seconds

A new steady-state concentration of approximately 3.5% is then attained within 1 minute

Contributor Factors:

Viscosity

Density

relative solubility of the carrier gas

the flow-splitting characteristics of the specific vaporizer

the concentration control dial setting

Safety Features:› Agent-specific, keyed filling devices › Overfilling is minimized› Firmly secured to a vaporizer manifold

(Prevent vaporizer tipping )

› Contemporary interlock systems (prevent the administration of more than one inhaled anesthetic)

Hazards:• Misfilling• Contamination • Tipping (transport “T” dial setting)• Overfilling• Underfilling (sevoflurane)• Simultaneous Administration of Inhaled Anesthetics • Leaks • Environmental Considerations (MRI)

DesfluraneBoils at 22.8°C

MAC: 6% to 7% (amount of desflurane vaporized over a given period is considerably greater than other

anesthetic drugs that cause excessive cooling of the vaporizer and significantly reduce its output)

Vapor pressures at 20°C enflurane 172, isoflurane 240, halothane 244, and desflurane 669 mm Hg

At 1 atm and 20°C, 100 mL/min passing through the vaporizing chamber would entrain

735 mL/min of desflurane versus 29, 46, and 47 mL/min of enflurane, isoflurane, and halothane

((to produce a 1% desflurane output))bypass flow would be approximately 73 L/min versus 5 L/min or

less for the other three anesthetics

Operating Principles of the Tec 6 and Tec 6 Plus

Simplified schematic of the Tec 6 desflurane vaporizer

The Datex-Ohmeda Aladin Cassette Vaporizer

The heart of the vaporizer is the electronically controlled flow control valve located in the outlet of the vaporizing chamber

Anesthetic Breathing Circuits

Mapleson Systems

Circle Breathing Systems

Mapleson Systems

prevention of rebreathing:

spontaneous

ventilation: A > DFE > CB

controlled ventilation: DFE > BC > A

Bain Circuit

The integrity of the inner tube can be assessed as described by Pethick

The Traditional Circle Breathing System

The most popular breathing system in the United States

“universal F” or “single-limb circuit,” (One version of the traditional circle system), has increased in popularity in recent years

A circle system depending on the amount of fresh gas inflow can be:

Semi open, semi closed, or closed A semi open (no rebreathing), requires a very

high flow of fresh gas. A semi closed system (some rebreathing of

exhaled gases), is the most common in the United States.

seven primary components of circle system

(1) a fresh gas inflow source

(2) inspiratory and expiratory unidirectional valves

(3) inspiratory and expiratory corrugated tubes

(4) a Y-piece connector

(5) an overflow or pop-off valve referred to as the APL valve

(6) a reservoir bag

(7) a canister containing a carbon dioxide absorbent.

Three rules must be followed

(1) a unidirectional valve must be located between the patient and the reservoir bag on both the inspiratory and expiratory limbs

(2) the fresh gas inflow cannot enter the circuit between the expiratory valve and the patient

(3) the overflow (pop-off) valve cannot be located between the patient and the inspiratory valve.

The main advantages of the circle system

(1) maintenance of relatively stable inspired gas concentrations

(2) conservation of respiratory moisture and heat

(3) prevention of operating room pollution.

Disadvantages Complex design

In a recent closed-claim analysis: more than a third (25/72) of malpractice claims resulted from breathing circuit misconnections or disconnections.

valves stick: Rebreathing, barotrauma or volutrauma

Obstructed filters located in the expiratory limb: have caused increased airway pressure, hemodynamic collapse, and bilateral tension pneumothorax