An alternative procedure is immersion in a bath of 100 % tricaine methanesulfonate( MS-222; Pharmaq) or phenoxyethanol( commercially known as Aqua-Sed; Vetark), ensuring that only the foot is covered and not the pneumostome [ 11 ], followed by an injection of pentobarbital into the foot.
Chelonians
To sedate chelonians before the administration of pentobarbital, alfaxalone can be administered intramuscularly, ideally into the forelimbs [ 12 ]. If sufficient sedation is not provided by the initial injection then a further dose can be given 20 minutes later.
The forelimbs are preferred because the renal portal system of reptiles can shunt blood from the caudal portion of the patient through the renal parenchyma, which would mean that a drug injected into the caudal part of the body might be excreted by the kidneys before it enters the rest of the circulation and takes effect.
Figure 1. Illustration by the author, showing the location of the opisthosoma in a typical arachnid species.
Small invertebrates
Euthanasia of these species should take place in a wellventilated room, and all staff should wear a mask while isoflurane on a cotton wool swab is placed in a small induction chamber with the patient. The patient should be left in the chamber for a minimum of 60 minutes to allow time for anaesthesia to be induced.
Once anaesthetised, the patient is immersed in 70 % alcohol or 10 % formalin [ 9 ]. To determine whether the patient is deceased, they should be placed in dorsal recumbency in an individual clear plastic container; the patient can be left unstimulated and assessed for any spontaneous movement or ability to right themselves [ 9 ].
Gastropods
Gastropods can be immersed in 5 % alcohol for 10 minutes to induce anaesthesia [ 10 ], followed by immersion in 70 % alcohol; the higher concentration of alcohol replaces the need to inject them with pentobarbital.
Smaller snails should be immersed in 70 % alcohol for 10 minutes and larger species such as African land snails should be immersed for 30 minutes [ 11 ]. Following immersion, check the patient is no longer conscious by stimulating them with a fine-gauge needle; if conscious, they will retract into their shell and a longer immersion will be required.
Injections of pentobarbital for euthanasia can be given into the jugular or dorsal tail vein. Subcarapacial routes can also be used. Intracoelomic injection should be avoided due to the highly alkaline pH of pentobarbital, which makes it caustic and therefore painful when administered extravascularly.
Alternatively, once the patient is sedated, pentobarbital can be injected intracardially via the ventral approach at the intersection of scutes on the plastron. While doing this, it is recommended not to tip the animal upside down as the heart will flop away from the injection site [ 13 ].
Doppler can be used to detect a heartbeat by placing the probe between the carapace( shell) and the inside of the front limb.
Lizards
Alfaxalone can be administered intramuscularly into the triceps or biceps muscles to sedate lizards before the administration of pentobarbital. Subcutaneous injection should be avoided as the drug may go into a fat pad, which results in a very slow uptake. If there is insufficient sedation after 20 minutes, then the injection can be repeated.
Injections of pentobarbital can be given into the jugular or ventral tail vein [ 14 ]. Figure 2( page 31) demonstrates the location of the tail vein in a bearded dragon during blood sampling.
Figure 3( page 31) shows a leopard gecko presented for euthanasia, which was placed on a heat pad throughout the procedure to help maintain the POTZ. A Doppler probe was used to confirm the absence of a heartbeat.
30 Veterinary Nursing Journal