You may have noticed that the knob on the halothane vaporizer on your UAM gets harder to turn over time. This is usually caused by an accumulation of thymol.

Halothane decomposes over time causing the release of halides, which can corrode metal components, particularly in the presence of moisture. For this reason, a stabilizing agent, thymol, is added to prevent decomposition. Since thymol does not volatilize along with halothane, it can accumulate in the vaporizer and it can reduce the vaporizer’s performance by clogging the wick and reducing the surface area for vaporization. Thymol can also gum up the vaporizer, making the control knob difficult to adjust, as well as compromising the internal mechanism. This is a safety hazard, so we want to ensure all UAM users know how to manage it.

In time thymol imparts a yellow color to the remaining liquid in vaporizers. Such discoloration is an indicator that the vaporizer should be drained and cleaned, and the discolored halothane discarded.

We recommend draining and replenishing halothane at intervals taking into consideration the hospital’s financial capacity and the frequency with which the vaporizer is used. At a minimum, we recommend draining the vaporizer every three months. Here’s how:

Preventing thymol build up in the halothane vaporizer

Materials and tools required: Metal bowl or container

1. Unscrew the filler cap on the front of the vaporizer. 

2. Place a metal bowl or container underneath the vaporizer. Halothane is corrosive and can damage the UAM if spilled.

3. Using the filler cap, insert the hex key on the bottom of the cap into the drain valve port just below the window on the front of the vaporizer.

4. Turn the filler cap counterclockwise to open the drain underneath the window.








5. When finished, turn the filler cap clockwise until the drain if fully closed. Do not over tighten.

6. Re-fill the vaporizer with halothane.

7. Dispose of the old anesthetic agent using your hospital’s procedures for disposing of medical waste.

Loosening a jammed control knob

If the control knob is stiff or will not move at all it may be the result of accumulated thymol. You can perform the following to try to loosen the knob:

  1. Remove the vaporizer from the UAM following the procedure on page 18 of the UAM maintenance manual.
  2. Take it outdoors, turn it upside down, and shake it vigorously followed by turning the knob until it becomes loose.
  3. If the knob loosens, it should be drained and rinsed with fresh agent.
  4. Attach the vaporizer back on the backbar and fill with fresh halothane.
  5. If the knob fails to loosen, you will need to send the vaporizer to our factory for cleaning or exchange.
Testing the Halothane Vaporizer
  1. With an oxygen cylinder connected and the concentrator switched off, set the oxygen flow to 5 liters per minute.
  2. Wait for the oxygen monitor to stabilize and calibrate to 100 %.
  3. Turn the vaporizer to 4%, wait 2 minutes and the reading on the oxygen monitor should drop from 100% to 96%.
  4. Repeat the oxygen measurements using the other concentration markings on the vaporizer.

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