2.4 Vaporizer

A vaporizer is an instrument designed to change a liquid anesthetic agent into its vapor and add a controlled amount of this vapor to the fresh gas flow (Figure 2.6 and 2.7). Volatile anesthetics are liquids at room temperature and atmospheric pressure. Vaporization, which is the conversion of a liquid to a vapor, takes place in a closed container, referred to as a vaporizer. The vapor concentration resulting from vaporization of a volatile liquid anesthetic must be delivered to the patient with the same accuracy and predictability as other gases (oxygen, nitrous oxide). 

Commonly, two to three anesthetic-specific vaporizers are present on the anesthesia machine. A safety interlock mechanism ensures that only one vaporizer at a time can be turned on. Turning on a vaporizer requires depression of a release button on the concentration dial, followed by counterclockwise rotation of the dial. This prevents accidental movement of the dial from the off to the on position. The location of the filler port on the lower portion of the vaporizer minimizes the likelihood of overfilling of the vaporizing chamber (>125 mL) with liquid anesthetic. 

Vaporizers are often constructed of metals with high thermal conductivity (copper, bronze) to further minimize heat loss. As a result, vaporizer output is nearly linear between 200C and 350C. Designation of vaporizers as agent specific and out of circuit emphasizes that these devices are calibrated to accommodate a single volatile anesthetic and are isolated from the anesthetic breathing system.

Figure 2:8 Vaporizer Fillers Filling the vaporizer using the key filler system (Figure 2.8 and 2.9) Move the vaporizer control to the OFF position.  Attach the appropriate key filler on the bottle containing the corresponding agent  Open the vaporizer  Push the plastic filling tube into the top of the vaporizer port with the bottle held low.  Tighten the screw on the filing tube.

Raise the bottle and ensure bubbles rise up in the bottle.  Pour the inhalant into the vaporizer to the "Full" inscription.  Do not overfill the vaporizer as it might result in excessive gas being delivered to a patient during anesthesia.  Lower the bottle and wait for the excess of drug to move from the tubing back into the bottle  Close the vaporizer.  Remove the plastic filling tubing and close the bottle. Figure 2:9 External feature of vaprizer and anesthetic volatile agents

Hazards of vaporizer 

• Vaporizers not equipped with keyed fillers have been occasionally misfilled with the wrong anesthetic liquid. 
• Contamination of anesthetic vaporizer contents has occurred by filling a halothane vaporizer with a contaminated bottle of halothane. 
• Overfilling: Improper filling procedures combined with failure of the vaporizer sight glass can cause overfilling and patient overdose. Liquid anesthetic enters the bypass chamber, and up to 10 times the intended vapor concentration can be delivered to the common gas outlet. 
• Under filling causes fall in vapor output 
• Vaporizer leaks occur frequently, and can potentially result in patient awareness during anesthesia. A loose filler cap is the most common source of vaporizer leaks. 
• Environmental pollution