Reptile Anesthesia

By | 2011-10-30

Restraint of reptiles may be performed without as much risk in the case of the debilitated animal in comparison to birds, for example. However, it is still worthwhile considering how to successfully and safely restrain the reptile patient in order for it to be anesthetised as well as some techniques that may make restraint less dangerous to animal and handler alike.

Initial Restraint Of The Reptile Patient

Points to consider include:

• Is the patient suffering from disease? Examples include patients with pneumonia, where mouth breathing and excessive oral mucus may be seen. Over-vigorous manual manipulation can exacerbate the problem.

• What is the species? Day geckos are extremely delicate and very prone to shedding their tails when handled. Similarly, species such as green iguanas are prone to conditions such as metabolic bone disease (MBD) whereby their skeleton becomes fragile and spontaneous fractures are common. Some reptiles are naturally aggressive, for example, snapping turtles, Tokay geckos and rock pythons. Other species are potentially dangerous, such as a venomous species of snake or lizard (e.g. rattlesnakes, cobras, Gila monsters and beaded lizards).

The need for restraint therefore needs to be considered carefully before physical attempts are made.

Restraint techniques and equipment

Order Sauria

This includes the members of the lizard family such as geckos, iguanas, chameleons and agamas.

Lizards come in many different shapes and sizes from the 1.2 m (4 foot) long adult green iguana, to the 10-12 cm (4-5 inch) long green anole. They have roughly all the same structural format with four limbs (although these may become vestigial in the case of the slow worm for example) and a tail. Their main danger areas therefore include their claws and teeth, and in some species, such as iguanas, their tails, which can lash out in a whip-like fashion.

Restraint is thus best performed by grasping the pectoral girdle with one hand from the ventral aspect, so controlling one forelimb with the thumb and the other between index and middle finger. The other hand is used to grasp the pelvic girdle from the dorsal aspect, controlling one limb with the thumb and the other again between index and middle finger. The lizard may then be held in a vertical manner with head uppermost to put the tail out of harm’s way. The handler should allow some flexibility in this method as the lizard may wriggle and overly rigid restraint could damage the spine.

The use of a thick towel to control the tail and claws is often very useful for aggressive lizards. Occasionally gauntlets are necessary for very large lizards, and for those that may have a poisonous bite (the Gila monster and the bearded lizard). It is important to assure that the lizard is not restrained with too much force, as those with skeletal problems such as metabolic bone disease may be seriously injured. In addition lizards, like other reptiles, do not have a diaphragm so over-zealous restraint will lead to the digestive system pushing on to the lungs and increasing inspiratory effort.

Geckos, as noted above, can be extremely fragile and the day geckos may be best anesthetised in a clear plastic container rather than physically restraining them. Other geckos have easily damaged skin so latex gloves and soft cloths should be used.

Small lizards may have their heads controlled between the index finger and thumb to prevent biting. Under no circumstances should lizards be restrained by their tail. Many will shed their tails if restrained in this way, but not all of them will regrow. Green iguanas, for example, will only regrow their tails as juveniles, i.e. <2.5-3 years of age. After this they will be left tail-less.

Vago-vagal reflex

There is a procedure which can be used to place members of the lizard and snake family into a trance-like state. It involves closing the eyelids of lizards (snakes eyelids are transparent and fused together over the eye as a ‘spectacle’) and placing firm but gentle digital pressure on to both eyeballs. Alternatively a ball of cotton wool may be placed over each eye and taped into place. This stimulates the parasympathetic autonomic nervous system which results in a reduction in heart rate, blood pressure and respiration rate. After 1-2 minutes of this, providing no loud noises are made, the lizard / snake may be placed on its side, front, back etc., so allowing radiography to be performed without further physical or chemical restraint. A loud noise or physical stimulation will immediately cause the lizard / snake to revert to its normal wakeful state.

Order Serpentes

This is the snake family. This order encompasses a wide range of sizes from the enormous anacondas and Burmese pythons, which may achieve lengths up to 9 m (30 feet) or more, down to the thread snake family, which may only be a few tens of centimetres long. However, they are all characterised by their elongated form with an absence of limbs. Their danger areas are their teeth (and in the case of the more poisonous species such as the viper family their fang teeth) and, in the case of the constrictor and python family, their ability to asphyxiate their prey by winding themselves around the victim’s chest / neck. Non-venomous snakes can be restrained by initially controlling the head. This is done by placing the thumb over the occiput and curling the fingers under the chin. Reptiles, like birds, have only the one occipital condyle so it is important to stabilise the neck occipital / atlantal joint. It is also important to support the rest of the snake’s body so that not all of the weight of the snake is suspended from the head. This is best achieved by allowing the smaller species to coil around the handler’s arm, so the snake is supporting itself. In larger species it is necessary to support the body length at regular intervals, so the help of several people may be necessary. Above all it is important not to grip the snake too hard as this will cause bruising and the release of myoglobin from muscle cells that will damage the kidney filtration membranes.

Poisonous species (such as the viper family, rattlesnakes etc.) or very aggressive species (such as anacondas, reticulated and rock pythons) may be restrained using snake hooks. These are 45-60cm (1.5-2 foot) long steel rods with a blunt-ended shepherd’s hook on the end and are used to loop under the body of a snake to move it at arm’s length into a container. The hook may also be used to trap the head flat to the floor before grasping it with the hand. Once the head is controlled safely the snake is rendered harmless unless it is a member of the spitting cobra family. These are unlikely to be encountered in general practice, but if they are, plastic goggles should be worn, as the poison is spat into the prey / assailant’s eyes, causing blindness.

Order Chelonia

This includes all land tortoises, terrapins and aquatic turtles, varying in size from the small Egyptian tortoises, weighing a few grams, to Galapagos species, weighing several hundred kilograms. The majority are harmless, although surprisingly strong. Exceptions include the snapping turtle and the alligator snapping turtle, both of which can give a serious bite, as can most of the soft-shelled terrapins. They also have mobile necks. Even red-eared terrapins may give a nasty nip!

For the mild-tempered Mediterranean species, the tortoise may be held with both hands, one on either side of the main part of the shell behind the front legs. For examination to keep the tortoise still he / she may be placed on to a cylinder / stack of tins which ensure that his / her legs are raised clear of the table, effectively balancing the tortoise on the centre of the underside of the shell (plastron).

For aggressive species it is essential to hold the shell on both sides behind and above the rear legs to avoid being bitten. For examination of the head region in these species it is necessary to chemically restrain them.

For the soft-shelled and aquatic species, soft cloths and latex gloves may be necessary in order not to mark the shell.

Order Crocodylia

This family is rarely seen in general practice and includes the crocodiles, both fresh and saltwater, the alligators, the fish-eating gharials and the caimans. Their dangers lie in their impressively arrayed jaws and their sheer size – an adult bull Nile crocodile may weigh many hundreds of kilograms and may live for up to 50 years or more. Readers are advised to consult standard texts for further information.

Aspects Of Chemical Restraint

Additional Supportive Therapy

Monitoring Anesthesia

Recovery And Analgesia

Reptiles often will recover rapidly from isoflurane anesthesia, but if other injectable drugs were used, recovery may be prolonged. It is thus essential to keep the reptile patient calm, stress free and at its optimum preferred body temperature. It may be necessary to keep the patient intubated with IPPV with oxygen if high doses of injectable agents have been used, until the reptile is once again breathing for itself. Care should be taken though, as high levels of oxygen actually suppress the stimulus for a reptile to breathe, as this is induced by a low level of PaO2 rather than high PaCO2 as in mammals. The use of doxapram at dose of 5 mg / kg IM or IV helps stimulate respiration.

Fluid therapy also helps to speed recovery, especially with agents such as ketamine which are cleared through the kidneys. Once recovery occurs, the patient should be encouraged to eat; if anorectic, the patient should be assist fed or stomach tubed.

The provision of analgesia, as is the case for other animal groups, is an important aspect of postoperative recovery (Table Commonly used analgesics in reptiles). Reptiles that have been given analgesia have been shown to have a quicker return to normality, i.e. eating, normal behaviour etc., than those who do not receive analgesia.

Table Commonly used analgesics in reptiles.

(SC = subcutaneously; IM = intramuscularly; IV = intravenously; PO = peros; q8h = every 8 hours; q24h = every 24 hours and so on)

Analgesic Dosage Dosage interval
Butorphanol 0.4 mg / kg SC, IM q6-8h
Buprenorphine 0.01 mg / kg SC, IM q8-12h
Meloxicam 0.1-0.2 mg / kg SC, IM, PO q24h
Carprofen 2-4 mg / kg SC, PO q24h (first day 4 mg / kg then decrease to 2 mg / kg)

 

Opioids have been shown to have some effect in reptiles: butorphanol at 0.4 mg / kg IM, IV or subcutaneously and buprenorphine at 0.02 mg / kg intramuscularly have been recommended.

Non-steroidal anti-inflammatory drugs (NSAIDs) also seem to be beneficial in reptiles. Carprofen at doses of 2-4 mg / kg intramuscularly initially, and then 1-2 mg / kg every 24-72 hours thereafter, and meloxicam at 0.1-0.2 mg / kg orally every 24 hours have both been recommended. It should be noted that all NSAIDs are potentially nephrotoxic and can have gastrointestinal ulcerative side effects, so fluid therapy and close monitoring are required.