Euthanasia by Carbon Dioxide

Note: Before implementing any Euthanasia procedure be sure to read the Euthanasia Procedure.

Carbon Dioxide

At the present time, many in the wildlife control industry consider euthanasia by carbon-dioxide (bottled gas only) induced narcosis to be the most user-friendly of the AVMA suggested methods. This is the method commonly used for the euthanasia of laboratory research animals. Using this method requires a chamber in which the heavier-than-air carbon dioxide is used to replace available oxygen in a container. The opportunity to euthanize the animal without injection, handling, or transfer is a definite advantage of this method. Carbon-dioxide is readily available at welding supply centers, is relatively safe to the wildlife technician, and will suppress an animal’s ability to experience pain prior to death.

CO2 setup for euthanizing wildlife. Photo by Wildlife Control Consultant

In order to euthanize by CO2 you will need the following equipment:

  1. A euthanasia chamber (can be built or purchased). Your chamber should be top loading and large enough to hold your largest cage. Some wildlife controllers have different size chambers for different size traps to save gas.

    • Chambers can be as simple as a wooden box or a plastic trashcan or barrel. Seal the bottom and sides with glue and/or caulk so that they are air tight. The lid, however, should NOT be air tight. Drill a hole for the CO2 delivery tube in the side of the box around 1 inch from the bottom. For size requirements see step 2 first. CO2 is heavier than air. As the gas enters the chamber, the heavier, CO2 displaces the lighter, room-air out the top of the box (which is why the lid should fit securely but not be air tight).

  2. Visit a welding supply company or bottled gas supplier. They will be able to provide you with the CO2 tank, gas regulator, flow meters and tubing.

  3. Be sure to ask the welding supply company about all relevant laws and regulations concerning the handling, storage, and transportation of pressurized tanks. Improper handling of tanks can result in serious injuries and property damage.
Here is how the flow rate can be calculated to your particular chamber.

Measure the chamber’s internal length, width, and height in inches. Multiply those three numbers (length x height x width) to determine the chamber’s volume in cubic inches (e.g. 13x13x33 inch tank = 5577 cu inches in volume). Divide by 61 to convert the volume to liters (5577 divided by 61 = 91.39661 liters). Then multiply 91.4 by .20 because we only want 20% of the tank to fill per minute. This comes to 18.28 liters. Therefore, you would need to set your gravity flow meter to a little more than 18 liters per minute and leave it on to fill the tank completely in 5 minutes.

After the chamber has filled, reduce the rate of flow to 3-5 lpm (lpm means liters per minute) to save gas. But do not turn the flow off as you will need to maintain positive pressure to prevent fresh air from reentering the chamber. Some animals like squirrels and adult raccoons will expire quickly. Others like skunks, infant raccoons, and woodchucks can take 30 minutes or more to die. In all circumstances, it is imperative that the animal’s death be confirmed. Confirm Death

1. Animal should look completely flaccid with no muscle tone.

2. Heart should stop beating (requires a stethoscope).

3. Pupils should not respond when touched.

4. Respiration should cease. (Caution shallow breathing may be very hard to see, especially when time between breaths is prolonged). Observe the animal for at least 45 seconds to confirm that respiration has ceased. 

Publications

  • AVMA panel on euthanasia (2007 Report of the AVMA Panel on Euthanasia, J Am Vet Med Assoc; 218:669-696) is available here.

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