Reptile Anesthesia and Analgesia

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AnalgesiaAnalgesia

David L. McRuer M.Sc., D.V.MDavid L. McRuer M.Sc., D.V.M.,.,

Dipl. ACVPMDipl. ACVPM

Wildlife Center of VirginiaWildlife Center of Virginia

,,



Reptilian resting metabolic rate (MR) is 1/10Reptilian resting metabolic rate (MR) is 1/10thth

to 1/3to 1/3rdrd

that of mammals of equivalent sizethat of mammals of equivalent size

Minimum and maximum OMinimum and maximum O22 consumption rates rangeconsumption rates range

from nearly 0 to that of mammalsfrom nearly 0 to that of mammals

A decrease in the cellular MR can result in reduction of A decrease in the cellular MR can result in reduction of

rug meta o sm an t ere ore ncreases n rug atencyrug meta o sm an t ere ore ncreases n rug atencyof onset, duration of effect, and time of recoveryof onset, duration of effect, and time of recovery



Ambient temperature is one of the main determinants of MRAmbient temperature is one of the main determinants of MR

↓↓ TempTemp → ↓ O→ ↓ O22 demand from tissues → ↓ in metabolicdemand from tissues → ↓ in metabolic

Species variation inSpecies variation in MR both between and withinMR both between and within taxataxa

Metabolic rate can increase 3Metabolic rate can increase 3--40 times after a meal and40 times after a meal and

..

It is unclear It is unclear whether this has any effect on reptile anesthesiawhether this has any effect on reptile anesthesia



In eneral:In eneral:

– – VaranidVaranid andand lacertidlacertid lizards have high MRlizards have high MR – – BoidBoid snakes and chelonians have lower MRsnakes and chelonians have lower MR

– –

MR than burrowing speciesMR than burrowing species

– – Lizards that eat insects or other vertebrates have higher MR thanLizards that eat insects or other vertebrates have higher MR than



Re tiles are ectothermsRe tiles are ectotherms – – ainin heat from environmentainin heat from environment

– – In warm conditions reptiles can increase HR and increase theIn warm conditions reptiles can increase HR and increase thedegree of leftdegree of left--toto--right shunting to send more blood to theright shunting to send more blood to the

eri her to be warmed thus ultimatel increasin core boderi her to be warmed thus ultimatel increasin core bod

temp.temp.

Large pythons and leatherback sea turtles are largeLarge pythons and leatherback sea turtles are large

movementmovement



Normal body temp is referred to as Preferred OptimalNormal body temp is referred to as Preferred Optimal

empera ure one or re erre o y empera ureempera ure one or re erre o y empera ure

(PBT) or Internal Thermal Set Point.(PBT) or Internal Thermal Set Point.

HypoxiaHypoxia--inducedinduced hyperthermia/hypothermia:hyperthermia/hypothermia:

– – At temperature extremes, a mismatch exists betweenAt temperature extremes, a mismatch exists between OO22 demanddemandand Oand O22 supply leading to hypoxia.supply leading to hypoxia.

– – ,,other activities such as dive times.other activities such as dive times.

h dration decreases PBTh dration decreases PBT



Cardiovascular system andCardiovascular system and

AnesthesiaAnesthesiaIntracardiacIntracardiac shuntin of blood occurs in theshuntin of blood occurs in the

noncrocodiliannoncrocodilian reptile ventriclereptile ventricle

This servesThis serves 3 functions:3 functions:

1)1) Stabilizes OStabilizes O22

content of the blood during respiratory pausescontent of the blood during respiratory pauses

-- --

systemic blood flowsystemic blood flow that facilitates the maintenance of bodythat facilitates the maintenance of body

temperature.temperature.

33 Ri htRi ht--toto--left shunt directs blood awa from lun s durin divinleft shunt directs blood awa from lun s durin divin




AnesthesiaAnesthesiaImplications for anesthesia:Implications for anesthesia:

– – Shunting is controlled by cholinergic and adrenergic factorsShunting is controlled by cholinergic and adrenergic factors – – Can effect the systemic arterial OCan effect the systemic arterial O22 content and uptake and eliminationcontent and uptake and elimination

of inhaled asesof inhaled ases

Large rightLarge right--toto--left shunts limitleft shunts limitamount of as u take earl inamount of as u take earl in

anesthesia and slow anestheticanesthesia and slow anesthetic

elimination during the end of elimination during the end of

anesthesiaanesthesia

Changes in level and directionChanges in level and direction

of shunting can account for of shunting can account for

unrepentant awakening duringunrepentant awakening during

surgerysurgery




AnesthesiaAnesthesiaBlood ressure controlled similar to mammalsBlood ressure controlled similar to mammals

Systemic arterial blood pressures vary considerably inSystemic arterial blood pressures vary considerably in

reptiles depending on species.reptiles depending on species.

and habitat), activity levels, and size of the reptile.and habitat), activity levels, and size of the reptile.



Respiratory System andRespiratory System and

AnesthesiaAnesthesiaLower OLower O consum tionconsum tion rate than mammalsrate than mammals

Large tidal volume but small surface area for gasLarge tidal volume but small surface area for gasexchangeexchange

No diaphragm therefore active inspiration and expirationNo diaphragm therefore active inspiration and expiration

Many muscles that control ventilation are alsoMany muscles that control ventilation are also




Variable across s eciesVariable across s ecies

More than 4% COMore than 4% CO22 causes ancauses an ↑ in tidal volume and a ↓ ↑ in tidal volume and a ↓

in resp frequency and minute ventilationin resp frequency and minute ventilation

-- 22

resp pattern.resp pattern.

High concentrations of OHigh concentrations of O22 can decrease resp. rate.can decrease resp. rate.

Therefore some studies have shown it is faster toTherefore some studies have shown it is faster to

recover rep es on room a r.recover rep es on room a r.



Liver has a slower MR than mammals and ma accountLiver has a slower MR than mammals and ma account

for the prolonged excretion of drugs (including somefor the prolonged excretion of drugs (including someanesthetic drugs) from the body.anesthetic drugs) from the body.



Drug Administration RoutesDrug Administration RoutesIM injectionIM injection

– – First pass effect in kidneys from rear limb injection is moreFirst pass effect in kidneys from rear limb injection is more

eore ca an a prac ca concern.eore ca an a prac ca concern.

– – However, still best to avoid nephrotoxic drugs and drugs mainlyHowever, still best to avoid nephrotoxic drugs and drugs mainlymetabolized by the kidneys when giving rear limb injectionsmetabolized by the kidneys when giving rear limb injections

– – SnakesSnakes – – epaxial muscleepaxial muscle

– – LizardsLizards – – forelimb, hindlimb, and tailforelimb, hindlimb, and tail

Caution: some animals can autotomize their tailsCaution: some animals can autotomize their tails

– – Chelonians: tricepsChelonians: triceps

Caution: avoid cranial surface of forelimbCaution: avoid cranial surface of forelimb –– radial nerveradial nerve



IV administrationIV administration

– – Snakes & lizardsSnakes & lizards –– ventralventral coccygealcoccygeal veinvein – – Freshwater turtles & tortoisesFreshwater turtles & tortoises – – dorsaldorsal coccygealcoccygeal veinvein

– –

IVIV injections decreaseinjections decrease the variabilitythe variability compared to IMcompared to IMinjections in reptilesinjections in reptiles



IO catheterizationIO catheterization

– – Best suited for lizardsBest suited for lizards – – Placed in femur or tibiaPlaced in femur or tibia

– –

given IV or IOgiven IV or IO



PremedicationPremedication

General purpose of premeds::

-- to ac tate an ng,to ac tate an ng,

catheterization, reducecatheterization, reducehandlin stress, and reducehandlin stress, and reduce

side effects caused by higher side effects caused by higher

doses of induction anddoses of induction and

De endin on the remedDe endin on the remed

drug(s), you may or may notdrug(s), you may or may notproduce sedation or decreaseproduce sedation or decrease

drugsdrugs – – therefore choosetherefore choose

according to your goals.according to your goals.



Anticholiner icsAnticholiner ics

– – Ex: atropine,Ex: atropine, glycopyrrolateglycopyrrolate – – Increase salivary viscosity predisposing patient toIncrease salivary viscosity predisposing patient to endotrachealendotracheal

– – Can alter intraCan alter intra--cardiac shunt fractions thereby altering responsecardiac shunt fractions thereby altering response

to inhaled anesthetics.to inhaled anesthetics.



PhenothiazinesPhenothiazines

– – Ex: acepromazineEx: acepromazine

– –

doses and have prolonged effectsdoses and have prolonged effects ––

not often usednot often used



Phenc lidinePhenc lidine

– – Ex:Ex: ketamineketamine,, telazoltelazol

e am nee am ne

– – AtAt subanestheticsubanesthetic levels, it produces analgesic effects andlevels, it produces analgesic effects and

sedationsedation – – Animals are in a cataleptic state marked by uncoordinatedAnimals are in a cataleptic state marked by uncoordinated

voluntary and involuntary muscle movementsvoluntary and involuntary muscle movements

– – KetamineKetamine does NOT PRODUCE Adoes NOT PRODUCE A SURGICALSURGICAL PLANE by itself PLANE by itself

– – Often combined with benzodiazepines or Often combined with benzodiazepines or αα22--antagonists toantagonists toproduce muscle relaxationproduce muscle relaxation



Phenc lidinePhenc lidine

TelazolTelazol ((tiletaminetiletamine andand zolazepamzolazepam))

– – Produces variable results in reptilesProduces variable results in reptiles

– – Less desirableLess desirable thanthan KetamineKetamine andand midazolammidazolam due to the longer due to the longer

duration of effect and longer recoveries.duration of effect and longer recoveries. – – Occasionally used in large lizards to reduce theOccasionally used in large lizards to reduce the injectableinjectable

volumevolume



PremedicationPremedication

BenzodiazepineBenzodiazepine

– – Ex:Ex: midazolammidazolam diaze amdiaze am

DiazepamDiazepam – – Not to be used IM as absorption is very poor Not to be used IM as absorption is very poor

MidazolamMidazolam

– – Often used in conjunction withOften used in conjunction with ketamineketamine for sedation and induction of for sedation and induction of

anesthesia inanesthesia in chelonians (turtles)chelonians (turtles)

– – Does not provide significant sedation when used alone in snappingDoes not provide significant sedation when used alone in snapping

turtles and painted turtles.turtles and painted turtles.



αα--anta onistsanta onists

– – provide sedation and muscle relaxationprovide sedation and muscle relaxation – – Clinical impressions suggest some degree of analgesia although notClinical impressions suggest some degree of analgesia although not

– – Medetomidine has a higher Medetomidine has a higher αα22::αα11 binding ratio than xylazine andbinding ratio than xylazine and

produces better anesthetic depth for intubations.produces better anesthetic depth for intubations. – – , ,, , ,

↓ ventricular pressures,↓ ventricular pressures,

– – Can be reversed with atipamazole given IM (not IVCan be reversed with atipamazole given IM (not IV –– hypotension)hypotension)



O ioidsO ioids

– – Poor sedatives in reptilesPoor sedatives in reptiles – – Commonly used for analgesia although few studies in reptiles.Commonly used for analgesia although few studies in reptiles.



Induction of AnesthesiaInduction of AnesthesiaPropofolPropofol (drug of choice if (drug of choice if IV catheter IV catheter

is present) can be used IO however is present) can be used IO however

has been associated with a nea inhas been associated with a nea in

green iguanasgreen iguanas

Induction with as anesthesia variesInduction with as anesthesia varies

due to breath holding.due to breath holding.

– – Stroking the lateral thorax mayStroking the lateral thorax may

promote breath takingpromote breath taking

Mean induction time onMean induction time on isofluraneisoflurane isis

20 min.20 min.

Muscle relaxants (Muscle relaxants (succinylcholinesuccinylcholine &&

atracuriumatracurium) work well for ) work well for

or amnesic propertiesor amnesic properties –– avoid regular avoid regular

use in anesthesiause in anesthesia



Easil visualized in most re tilesEasil visualized in most re tiles

RostralRostral in snakes, behind thein snakes, behind thetongue in lizards and chelonianstongue in lizards and chelonians

Complete tracheal rings inComplete tracheal rings in

chelonians andchelonians and crocidilianscrocidilians,,

therefore usetherefore use uncuffeduncuffed endotrachealendotracheal tubestubes

Thick mucous in retiles can plugThick mucous in retiles can plug

u esu esRostralRostral bifurcation of trachea inbifurcation of trachea in

– –

intubationintubation



MACMAC

– – IsofluraneIsoflurane – – reptiles range = 1.54%reptiles range = 1.54% – –3.14%3.14%

– – – – ’’ == ..

0.5%0.5%

– – MAC values can vary based on techniqueMAC values can vary based on technique

, ,, ,

species differences, and rightspecies differences, and right--toto--leftleft

intracardiacintracardiac shuntingshunting

– – -- --

from the lungsfrom the lungs – – therefore less gas can betherefore less gas can beabsorbed.absorbed.

– –



IsofluraneIsoflurane

DoseDose--dependant cardiovascular depressiondependant cardiovascular depression MAYMAY occur occur

in reptilesin reptiles

A doseA dose--dependant sevoflurane study with desertdependant sevoflurane study with desert

tortoises did not show a decrease in ventricular bloodtortoises did not show a decrease in ventricular blood

..

4X MAC with isoflurane in green iguanas does not4X MAC with isoflurane in green iguanas does not

induce cardiovascular arrest.induce cardiovascular arrest.



OO rate = 50rate = 50--100 ml/k /min for rebreathin s stem100 ml/k /min for rebreathin s stem

OO22 rate = 200rate = 200--300 ml/kg/min for Bain system300 ml/kg/min for Bain systemFor most vaporizersFor most vaporizers – – 200ml/min is required for 200ml/min is required for

vaporizer accuracy.vaporizer accuracy.

Ventilators = often necessaryVentilators = often necessary – – use one designed for use one designed for

..



Reflexes:Reflexes:

– – When induced with inhalent anesthesia, muscle relaxation startsWhen induced with inhalent anesthesia, muscle relaxation startsat midbody, then cranially, then caudally.at midbody, then cranially, then caudally.

– –

– – Corneal reflex should still be present (not in snakes and someCorneal reflex should still be present (not in snakes and some

lizards due to the spectacle).lizards due to the spectacle).



Cardiovascular:Cardiovascular:

– – Small bell stethoscope on wet gauze placed on the animalSmall bell stethoscope on wet gauze placed on the animal – – Esophageal stethoscope advanced slowing to the point of Esophageal stethoscope advanced slowing to the point of

..

– – Ultrasonic Doppler device with a pediatric probeUltrasonic Doppler device with a pediatric probe

– – The Doppler can also be used for measuring changes in bloodThe Doppler can also be used for measuring changes in blood



ECGECG – – measures heart rate and rh thm. Re tiles havemeasures heart rate and rh thm. Re tiles have

an SV wave proceeding the P wave.an SV wave proceeding the P wave.LizardsLizards – – place left and right forelimb leads on cervicalplace left and right forelimb leads on cervical

reg on o ncrease s gna s rengreg on o ncrease s gna s reng

SnakesSnakes

– – --

– – Place leads two heart lengths in front of and behind the heartPlace leads two heart lengths in front of and behind the heart

CheloniansChelonians

– – Leads placed on the skin between neck and forelimbs.Leads placed on the skin between neck and forelimbs.Attaching leads to needles or a stainless steel loop mayAttaching leads to needles or a stainless steel loop may



Re tiles do not breath well on their own under Re tiles do not breath well on their own under


Recommendation:Recommendation:

– – Mechanical ventilation at 2Mechanical ventilation at 2--6 breaths/min, 156 breaths/min, 15--30 ml/kg tidal30 ml/kg tidal

volume, peak airway pressure less than 10 cm Hvolume, peak airway pressure less than 10 cm H22OO

Only one study has shown a relationship betweenOnly one study has shown a relationship betweenhemoglobin saturation from pulse oximetry and arterialhemoglobin saturation from pulse oximetry and arterial

hemoglobin saturation (green iguanas). Other studieshemoglobin saturation (green iguanas). Other studies





Best to reh drate before anesthesiaBest to reh drate before anesthesia

IV or IO is best however, IP and SQ may be usedIV or IO is best however, IP and SQ may be usedReptiles have a higher % of there body water in theReptiles have a higher % of there body water in the

intracellular space compared to mammalsintracellular space compared to mammals



Best to kee animals in the hos ital at the u er ran eBest to kee animals in the hos ital at the u er ran e

of the POTZ.of the POTZ.

At lower environmental temperatures, you can seeAt lower environmental temperatures, you can see

pro onge rug e ec s, mpa re mmune s a us an ra epro onge rug e ec s, mpa re mmune s a us an ra e

of healingof healing



Preemptive analgesia:Preemptive analgesia: ↓ central sensitization, facilitate↓ central sensitization, facilitatehealing, prevent detrimental neurohumeral response to pain, ↓ healing, prevent detrimental neurohumeral response to pain, ↓

amount of maintenance drugs during anesthesiaamount of maintenance drugs during anesthesia

Neuroanatomy consists of endogenous antinociceptiveNeuroanatomy consists of endogenous antinociceptivemechanisms, demonstrable modulation of pain by drugs,mechanisms, demonstrable modulation of pain by drugs,

neural tract in the brain and spinal cord that suggest a meansneural tract in the brain and spinal cord that suggest a meansof mediating descending inhibition of nociception.of mediating descending inhibition of nociception.

O ioid rece tors are found in re tiles and involved withO ioid rece tors are found in re tiles and involved with

reproduction and thermoregulation.reproduction and thermoregulation.

..



Im ortant to know normal s ecies behaviors to knowIm ortant to know normal s ecies behaviors to know

what behaviors may be interpreted as pain or stress.what behaviors may be interpreted as pain or stress.

Three main classes of analgesic drugs:Three main classes of analgesic drugs:

1)1) Local anestheticsLocal anesthetics

2)2) NSAIDSNSAIDS

3)3) OpioidsOpioids



– –Interu t nocice tion from the level of the nocice tor toInteru t nocice tion from the level of the nocice tor to

the spinal cord.the spinal cord.

Pay special attention to toxic dose as you are oftenPay special attention to toxic dose as you are often

wor ng w sma pa en s.wor ng w sma pa en s.

Lidocaine and Bupivicaine (longer Lidocaine and Bupivicaine (longer--lasting 1lasting 1--2 mg/kg) are2 mg/kg) are

most often used.most often used.



--Act to modulateAct to modulate nociceptionnociception in the periphery and spinal cordin the periphery and spinal cord

Central nervous system is not as complex, therefore centralCentral nervous system is not as complex, therefore central

..

Several recent studies have tested NSAIDS on reptiles:Several recent studies have tested NSAIDS on reptiles: – – TrnkovaTrnkova S. et.al.S. et.al. EffectEffect of nonof non--steroidal antisteroidal anti--inflammatoryinflammatory drugs ondrugs on the blood profile in the greenthe blood profile in the green

iguana (iguana (Iguana Iguana iguana iguana). ). Veterinarni Veterinarni Medicina Medicina, 52, 2007 (11): , 52, 2007 (11): 507 507– –511511

– Hernandez-Divers, S. J. Meloxicam and reptiles - a practical approach to analgesia. Small animal and

exotics. Proceedings of the North American Veterinary Conference, Volume 20, Orlando, Florida, USA, 7-11

January, 2006 2006 pp. 1636-1637

Assume sideAssume side--effects as per other species.effects as per other species.



--Does not tend to induce statisticall si nificant chan esDoes not tend to induce statisticall si nificant chan es

in physiological parameters.in physiological parameters.

DoseDose--dependant response observed with morphine anddependant response observed with morphine and

meper ne n croco es w ce ng e ec s.meper ne n croco es w ce ng e ec s.

– – Latency of action = 30 min, Duration = 2Latency of action = 30 min, Duration = 2--2.5 hours.2.5 hours.



--Buprenorphine:Buprenorphine:

– – PartialPartial µ agonist with someµ agonist with some κκ antagonist propertiesantagonist properties

– – Unpublished studies indicate that this is a much better analgesicUnpublished studies indicate that this is a much better analgesicin turtles compared to butorphanol.in turtles compared to butorphanol.Kummrow: Pharicokinetical basis for dru recommendations of Kummrow: Pharicokinetical basis for dru recommendations of Burenorphine in redBurenorphine in red--eared sliders, 2006 AAZV conferenceeared sliders, 2006 AAZV conference

ButorphanolButorphanol:: – – StrongStrong κκ agonist and weak µ antagonistagonist and weak µ antagonist

Slavky: Morphine but not butorphanol causes analgesia and not respiratorySlavky: Morphine but not butorphanol causes analgesia and not respiratorydepression in reddepression in red--eared sliderseared sliders , 2006 AAZV conference, 2006 AAZV conference

Fleming: Use of thermal threshhold test response to evaluate theFleming: Use of thermal threshhold test response to evaluate theantinociceptive effects of butorphenol in juvenile green iguanasantinociceptive effects of butorphenol in juvenile green iguanas , 2006 AAZV, 2006 AAZVconferenceconference



CasesCasesMyiasis in an Eastern Box TurtleMyiasis in an Eastern Box Turtle

Ketamine 10 mg/kgMedetomidineMedetomidine 0.2 mg/kg

.

Isoflurane



Black rat snakeBlack rat snake

Ketamine 12 mg/kg

MedetomidineMedetomidine 0.3 mg/kg

Buprenorphine 0.04 mg/kg

Isoflurane

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Reptile Anesthesia and Analgesia

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