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

 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)

Boils 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

Simplified schematic of the Tec 6 desflurane 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

prevention of rebreathing:  spontaneous ventilation: A > DFE > CB  controlled ventilation: DFE > BC > A

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

 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.

 (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.

 (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.

 (1) maintenance of relatively stable inspired gas concentrations  (2) conservation of respiratory moisture and heat  (3) prevention of operating room pollution.

 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