Inhalant Anesthetics
Several inhalant anesthetics have been used for wildlife
euthanasia. Halothane is often the inhalant selected because
it rapidly induces unconsciousness. Enflurane also rapidly
induces unconsciousness, but seizures under deep anesthesia
from enflurane are more common than from halothane.
Methoxyflurane vaporizes slowly and, therefore, has a longer
anesthetic induction time, which can cause the bird to become
agitated. Isoflurane has a rapid induction time, but its
odor can cause the animal to hold its breath, thereby delaying
unconsciousness. Nitrous oxide has a low potency and is
available only in gas form; other anesthetics are purchased
as a liquid, and they vaporize at room temperature and normal air pressure. Nitrous oxide can be used in combination
with other inhalants to speed anesthesia, but it should not be
used alone because animals often become agitated and distressed
before they lose unconsciousness.
To administer an inhalant anesthetic for euthanasia of an
individual bird, prepare a cone (from a syringe case or other
plastic material) that will fit snugly when it is placed over
the beak and nares (Fig. 5.2). Pour a small amount of the
anesthetic agent on a piece of cotton, tissue, or cloth, and
place it in the narrow part of the cone. Restrain the bird; put
the open end of the cone over the beak and nares, and continue
restraining the bird until it becomes unconscious. Restraint
can then be discontinued, but keep the cone in place
for several minutes before checking to assure that the bird is dead. Alternatively, place an individual bird, or several small
birds, in a cage or crate; cover it with plastic or place the
cage in a covered plastic barrel. Place the cotton, tissue, or
cloth soaked with anesthetic agent inside the chamber with
the birds and tie or otherwise seal the plastic to prevent the
vaporized agent from escaping (Fig. 5.3). Cold temperatures
will decrease the rate at which the liquid becomes gas. Small
mammals can be euthanized by similar procedures.
A animal exposed to anesthetic gas may pass through an
“excitation phase” before it becomes unconscious; it may
vocalize and appear to struggle for a short time. This behavior
may be distressing to the casual observer and it can be
dangerous for the handler, depending on the species. It is
important to assure that the animal is dead, and not just unconscious,
before shipment, necropsy, or disposition. After
removing the animal from the gas environment, it may wake
up quickly, with little warning. Remember this when working
with raptors, carnivores, and other biting animals.
Because all of these gases constitute a human health hazard,
including the potential to cause spontaneous abortion
and congenital abnormalities, the workplace must be wellventilated.