Spotlight on Anesthesia & Analgesia in Reptiles

2024 Spotlight

This 2024 webinar was an updated version of Dr. Nevarez’s 2016 presentation.

 

Abstract

The study of anesthesia and analgesia in reptiles has significantly expanded and there is readily available information in the literature to help make sound clinical decisions for these patients. While reptiles are often thought of as stoic animals that do not show many behavioral changes, this is a misconception and anyone working with them should become familiar with the signs of pain and discomfort. It is also important to remember that the analgesic effect provided by general anesthesia is short lived, up to the point of recovery, and analgesic protocols must be instituted in all case when painful stimuli is unavoidable. We must think of anesthesia and analgesia as being two different components of one modality, both being essential for its success.

Download the 2-page abstract [DOCX] [PDF]

 

Outline

Download the 7-page outline of Dr. Nevarez’s presentation [DOCX] [PDF]

Lecture Objectives
I. Definitions

  1. General anesthesia
  2. Sedation
  3. Tranquilization
  4. Analgesia

II.Objectives

  1. Balanced anesthesia
  2. Preemptive analgesia

III. Anatomy & physiology

  1. Poikilothermic species
  2. Cardiopulmonary system
  3. Renal-portal system

IV. Signs of pain

  1. Change in normal behavior
    1. Aggression in passive animal
    2. Passive behavior in normally aggressive animals
  1. Reluctance to move
  2. Abnormal ambulation
  3. Dull, closed eyes
  4. Anorexia
  5. Hunched posture
  6. Elevated, extended head
  7. Lameness
  8. Decreased tendency to coil (snakes)
  9. Aerophagia
  10. Color changes (darker or paler)

V. Analgesia

  1. Pure mu agonists
    1. Morphine
    2. Hydromorphone
    3. Fentanyl
  2. Weak mu agonist
    1. Tramadol
  3. Nonsteroidal anti-inflammatory drug
    1. Cyclooxygenase (COX)-2 specific inhibitor
    2. Meloxicam
  4. Regional analgesia/anesthesia
    1. Intrathecal spinal analgesia

VI. Indications for…

  1. Tranquilization
  2. Sedation
  3. Anesthesia
VII. General anesthesia

  1. Injectable agents
    1. Ketamine
    2. Dexmedetomidine
    3. Midazolam
    4. Propofol
    5. Alfaxalone
  1. Inhalational agents
    1. Isoflurane
    2. Sevoflurane
  2. Premedication
  3. Induction
  4. Maintenance
  5. Examples

VIII. Injection sites

IX. Intubation

X. Patient monitoring

  1. Reflexes
  2. Heart rate
  3. Respiratory rate
  4. Temperature

XI. Cardiovascular support

  1. IV access
  2. IO access

XII. Temperature support

  1. Hypothermia
  2. Preventing hypothermia

XIII. Recovery

  1. Wean off gas before the end of procedure
  2. Maintain O2 at low flow rate
  3. KEEP WARM!!!!!!!!!!!!!!!!
  4. Breathing stimulus

XIV. Keys to success

XV. Not every patient needs drugs

 

 

 

 

 

About the presenter

Dr. Nevarez became a Diplomate of the American College of Zoological Medicine and the European College of Zoological Medicine (Herpetology) in 2011. He has been a faculty member of the Zoological Medicine service at the LSU School of Veterinary Medicine since 2003 where he also serves as director of the Wildlife Hospital of Louisiana. [MORE]

 

Webinar recording

 

Download the 2024 presentation

Download Dr. Nevarez’s PowerPoint presentation:  PDF

 

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2024 Expert Q&A

Although most questions were addressed during the live event, Dr. Nevarez generously answered the remaining questions in a follow-up meeting. His answers are from a lightly edited transcript.

 

ANATOMY AND PHYSIOLOGY

I have recently heard that atropine helps with right to left shunting. Is that true?

As a follow-up to this question, the attendee provided a link to an open-access paper by Kristensen et al 2023.8

I actually looked up a lot of the other references that were involved with these papers…so if you want to share them you can…4-6

…The key component here is that YES, these investigators, and some of the previous work, has done a really good job at setting up a model…where they have shown that with atropine you can minimize shunting and you can improve the minimum anesthetic concentration.

The one thing we need to be careful clinically is that none of these studies have shown the impact that this has on oxygenation, on the rest of the physiology of the animals (i.e. blood gases, etc.), because they didn’t measure any of that. In mammals, in rats and humans for example, it’s been shown that atropine causes a V/Q mismatch (a ventilation-perfusion mismatch). So just because you’re getting better absorption of the gas anesthetic because we have more blood flow to the lungs, does not necessarily mean you’re getting good oxygenation. I was talking to one of our anesthesiologists about this yesterday, horses are a great example where you can have a horse anesthetized under gas anesthesia, but they still have a V/Q mismatch and it’s very difficult to ventilate for them.

…This right to left shunting is really a big concern when we have gas anesthesia. So [as we discussed] in the main presentation, we should not be relying on gas anesthesia alone. And I find it interesting that people are always so focused on this in reptiles because there’s such a focus on total intravenous anesthesia now on the mammalian side. People have asked me about [total IV anesthesia] in reptiles too. It’s not something that we do because of the difficulty accessing the vessel sometimes…

We have to be careful to look at these articles, the entirety of the Kristensen et al article, look at the discussion because here the author’s go into a lot of the caveats… And I think the investigators…do a good job of explaining what the caveats are for using [atropine]. So I think we have to be careful…There’s at least two papers, if not three, that have shown that atropine can certainly counteract the right-to-left shunting, but this was in otherwise healthy animals [under] ideal conditions.

So the main question was does atropine help right-to-left shunting? Is it true? Yes, it is absolutely true. The literature shows that. The follow up to that is:  Should we be using atropine clinically In our cases? There’s not enough data yet to suggest that it’s safe. I think this model [described by Kristensen et al] can be used to dehydrate reptiles and then see what impact this has. And most of the patients we’re dealing with are not healthy reptiles. They’re sick reptiles. We have to take that into consideration. So [these are] some great studies and I had a good time reading them and it’s fascinating data, but I think this is another avenue again for somebody to develop a whole PhD or multiple PhDs using this model to then look at the impact that might have on our patients.

 

LOCAL OR REGIONAL ANESTHESIA

If opting for a sedation plus local anesthesia protocol, how long do you…normally have to wait for the local anesthetic to take effect?

So, in reptiles we don’t know… In other species, at least from human medicine, we know it should be at least 5-10 minutes that you have to wait for the infiltration…to have full effect and then you can start making the incision.

 

How do you usually manage phallus prolapse during intrathecal anesthesia in tortoises? 

So, with intrathecal injections, you most definitely will see the phallus prolapse.

  • If you were planning to do a phallus amputation, then your phallus will prolapse easily. You can do your amputation and then move on.
  • ..you’re doing [a different procedure], the only important thing is you keep the phallus moist. …We’ll actually put a lot of lubricant around the phallus and wrap moist gauze around it to keep [the phallus] moist…during that period.

 

TRANQUILIZATION

With physical restraint, i.e. in crocodilians, do you use low-dose midazolam for stress reduction?

Yes…you certainly can. We don’t have any data to say for sure. [Midazolam] does reduce stress, but you certainly can use low-dose midazolam as a tranquilization or even a sedation protocol.

For example, we had a sea turtle come in yesterday for a CT and he was pretty feisty. So, we…gave him 1 mg/kg of midazolam that [provided] full sedation. He was out, he was unaware of the surroundings. We got the CT done and then reversed it with flumazenil. So that’s a single-drug sedation protocol

…The one challenge in crocodilians is that sometimes a single drug dose will not [provide] sedation. You can get a tranquilization, but not necessarily a full sedation.

 

ANALGESIA

I regularly do surgery on rattlesnakes and copperheads, using meloxicam as a non-steroidal, and you mentioned that meloxicam may not be as efficacious in snakes as we would like.  Do you use carprofen, and do you have any dosages and/or concerns?  Other suggestions?  And do you ever use butorphanol?

Yeah, so this is based on that one study that came out a few years ago that suggested or showed that snakes have more cyclooxygenase (COX)-1 versus COX-2.12 So, the short answer is no, we still don’t use meloxicam. Again, that’s one of those studies that there needs to be more data collected on that.

…No, I don’t use butorphanol…Again, there’s still very little data in snakes as to exactly what’s going to help.

When we have snakes that undergo surgery, the one thing that I have been using more has been fentanyl. I’ve been using fentanyl patches. This is strictly based on the fact that we know they can absorb the fentanyl patches7,17, and anecdotal evidence from some colleagues [at the University of] Wisconsin that have been using this. Again, there’s no hard data on this, but …I use fentanyl patches on snakes just because some of the data suggests that fentanyl might be better.

…We always use the smallest patch available—you never should cut those patches because the distribution is not even throughout the patch. So we use the smallest patch available…and we keep an eye on the animal and monitor for any significant signs of sedation within the first 6-12 hours to make sure they’re not getting [an] overdose with the fentanyl…Typically, we’re talking about snakes that are going to be at least in the 500 grams to 1 kilogram range…[If] the animal becomes very sedate, we’ll remove the patch because that’s an indication that they’re potentially getting an overdose. But if the animal doesn’t seem sedate, then we’ll leave the patch on… There’s no specific guidelines… We typically…remove [the patch] after [about] a week and then monitor. We’re not doing just the fentanyl…patch…we’re doing everything else that we can to [keep the patient] comfortable, [maintaining] them in the right temperature, etc…

…Snakes are the most frustrating ones because we’re trying to do the best we can for them, but we honestly don’t know if we’re really meeting their needs. So again, I think that’s where doing multimodal analgesia is important. So try to do a local block before we do the surgery or [provide] regional [anesthesia], if you can. Try to use an opioid…[S]ome people say they see good results with tramadol. The big thing is dosage…tramadol probably requires higher doses than what we’re used to. So, if [you] think clinically [that] you’re seeing good results, …use whatever works for you as long as you have a balanced plan to…approach analgesia.

 

INTUBATION

How far do you insert the endotracheal tube?

That’s a great question… To know how far to insert the tube, you have to understand the anatomy–there’s no other way around it…If you have a [radiograph] of the patient, then…measure [the trachea] on the x-ray [film] to see how far you can go. If you don’t [have an x-ray, then look for your species of interest] online. You can go online and find x-rays of bearded dragons or chelonians or whatever.

  • [Intubation of] a snake is no big deal, right? With a snake, you can [insert the tube] pretty far. You’re rarely going to hit the tracheal bifurcation.
  • In lizards, immediately past the neck, typically you have the [tracheal bifurcation]…I would say if you have to do an external measurement, don’t go past the base of the neck…Lizards [generally] have very short necks.
  • …So the biggest group of species where you have to be careful is the chelonians because in some chelonian species, the tracheal bifurcation is a little bit more cranial…[Therefore] in chelonians, as a general recommendation, just [passing the endotracheal tube to the] mid-neck region will be the safest thing. Can you go deeper in some of them? Sure you can, but if you don’t have [a radiograph, or if] you’re unfamiliar with that species, just keep it right at the mid-neck level.

  

EXTUBATION

When should we take endotracheal tubes out after the surgery? What signs do we need to see? Will [reptiles] be like cats and dogs? 

[Extubation in reptiles] is most definitely not like cats and dogs. Reptiles are very stubborn when it comes to this, and there’s a lot of factors that influence this. Based on my clinical experience, what I can say is that because of the anatomy and physiology of reptiles, as long as they’re getting ventilated [well]…they will have no desire to breathe whatsoever. So [in some] patients, even if you reduce the oxygen, [even if] you put them on an Ambu® bag…they are just there and they don’t seem like they want to respond. Sometimes what in those cases, what happen is those animals are getting so well-ventilated that they simply just are metabolizing the drugs and hanging out and just doing their thing, and they’re stubborn. So, what we’ll do [in those cases] is we’ll actually slow down. If we’re [ventilating the reptile] four to six breaths a minute. I’ll slow it down to two breaths a minute. And sometimes what I also find is [gently] moving that endotracheal tube will sometimes stimulate [the reptile].

It’s also a big difference if we have an apneic reptile versus…one that’s breathing. So we obviously want the reptile to be breathing on their own before we extubate them, but sometimes even if a reptile is apneic after the procedure, manipulate that endotracheal tube a little bit, start squeezing their toes, squeezing the limbs, try to really wake them up. We also sometimes use that acupuncture point, the GV-26–that one is right in the middle of the nose, right between the nostrils that has been shown in mammals to elicit a [stimulatory] response.

In some of the studies in reptiles, we talk about epinephrine and how you can recover them. But again, with epinephrine, all you really is doing is improving the blood flow, which is improving the metabolism. But…the big concern is how is this animal doing metabolically? But it’s very difficult for us to get blood gases. So in other species, you wouldn’t just give epinephrine just for the sake of it to wake them up. But if you have one that’s bradycardic, yeah, that makes a little bit more sense.

So stimulation is key. So if you have [a patient] that is apneic, stimulate, stimulate. Make sure you reverse anything that can be reversed, including the opioids. And then you can add the opioids [back] later on because those opioids can contribute to significant reverse depression on these patients.

Once they’re breathing on their own, sometimes I’ll extubate them and just monitor. If they’re opening the glottis on their own and their trachea and they’re breathing on their own, fine. I’ll leave them extubated and then come and check on them and make sure they’re continuously breathing. We have the advantage of having students, so we can leave a student there monitoring the [patient the] whole time, but if you don’t have that, just set a timer for every 5 minutes and come and make sure that they’re still breathing well on their own. But you can most definitely extubate them before they’re fully awake, as long as they’re breathing and they continue to open that glottis on their own they’re fine.

 

INTRACARDIAC INJECTION

Although a question about intracardiac injections was answered during the live event, Dr. Nevarez also shared information about a case example.

 

PERSONAL PROTECTIVE EQUIPMENT

Would you please comment on the use of disposable gloves when handling reptiles? I noticed in most photos, no gloves (PPE) are used.

I get this question a lot and I will be honest and tell you that I rarely wear gloves with reptiles. The reason being that if you work with enough reptiles, [such as] sulcatas and iguanas…, your gloves are going to end up getting ripped within a few minutes of handling. So, it kind of defeats the purpose. So, I wash my hands A LOT. I keep a bottle of hand lotion in my office because I wash my hands so much during the day that they’re always dry. So if I have cuts and scrapes in my hands, I’ll be more aware and will potentially wear gloves. But reptiles, unless it’s a snake, [many] of them are going to rip right through those gloves.

Yes, I understand the importance of PPE. I advocate [its use], and I tell our students and everybody, if you’re comfortable wearing them, wear them. But with reptiles, a lot of times it becomes very difficult. They get torn, and let’s face it, we don’t handle our reptiles at home with gloves and PPE. So I think it is about hygiene. It’s about making sure that obviously as soon as I’m done with that reptile patient and I put it down, I go wash hands. I’m not going to touch anything else. If I use my stethoscope, I’m going to disinfect my stethoscope afterwards. So you do have to be extra vigilant of anything that you touch, you want to disinfect. But yeah, it’s just a matter of getting in that habit of being judicious about [cleaning] your hands and disinfecting surfaces.

 

INTERDISCIPLINARY RESEARCH/ANIMAL WELFARE  

I shadowed a surgery on a wild snake that was having a radio transmitter implanted. It was being used for a conservation research project. I was shocked to observe the surgeon’s assistant heated up a snuggle-puck in the microwave for 5 minutes and placed the snake on the piping hot plate and spun it around to wake it up. I was told this was standard to wake them up faster. Is this something that actually was considered safe and appropriate? Many of the snakes we tracked (radio telemetry) had burn marks appear ventral ~13 days later.  The surgeon refused to consider that his spinning of the snakes on the hot plates could possibly be linked to the ventral burns.

…I think that is a good point and a good comment, and I think that that is the importance of us as veterinarians doing a better job of working with our biologists colleagues and letting them know what we can bring to the table.

I was lucky enough to be involved in a telemetry study with Louisiana pine snakes—a pretty rare species—a number of years ago…And after conversations with [the biologists about] their concerns, they actually would trap the snakes, bring them to LSU, where we would do the surgeries at LSU in the OR… So [the snakes] got the benefit of balanced anesthesia and analgesia. (Although we know in snakes we don’t know what’s really analgesic). They received fluids and antibiotics, the implants were placed in a sterile manner, and those animals were kept in captivity for a week post-surgery to monitor them and then give them a second injection of antibiotic before release. So that actually led to the fact that none of those snakes ended up dying from complications from the surgery…

So yeah, I mean, it is a common frustration sometimes, but I think as veterinarians, we need to do a better job of…speaking with the biologists and bringing [our] knowledge…and saying, Hey, this is how we, as veterinarians, can help improve your success rate…Because we can help reduce infection [rates]. [W]e can help improve the success of these animals being released and moving faster [so they’re less likely to be preyed upon]…[W]e can improve the success of your research colony.

So working with the biologist hand in hand and everybody bringing something to the table is important. As to this specific situation, I’m not sure about this hot plate technique, what exactly that is. I think I know what the snuggle pucks are, and I hate them because they always have hot zones in them. So I’m never a big fan of that. If you’re going to use anything like that, you always, always need to have a barrier between the animal and the material so they don’t get burns.

…You have to remember that as veterinarians, animal welfare is a big part of our training…Not to say that biologists don’t think about [animal welfare], but it is not a big part of their training overall…So I think that’s a big gap in their area. Just like we have gaps in veterinary medicine too, but [animal welfare concerns] are something we can help improve in that field, for sure.

 

 

The following questions were answered by the moderator.  

CATHETERS

Is IO not painful?…[Does the patient always] need to…be sedated?

Generally, YES, intraosseous catheter placement is considered painful and sedation or general anesthesia along with local analgesia is generally utilized. Occasionally only local anesthesia is used in a moribund patient, but that is always a difficult clinical decision that must be carefully evaluated…You may find the LafeberVet article “Catheters in Reptiles” of interest…It includes a video as well as text with still images.

 

Can you use most of the IV induction/premed agents at the same dose in an IO catheter?

Yes, the same dose is used when administering drugs via an intrasseous catheter.

 

MONITORING

 If corneal reflex loss is normal, is there a good reflex to watch to know if they are too deep?

Generally, when the corneal reflex is lost (in reptiles with eyelids), other reflexes are also lost, such as withdrawal, the Bauchstreich reflex, and response to cloacal pinch. You may find the LafeberVet article “Anesthetic Depth in Exotic Animals” of interest. Here is a direct link to the reptile reflex section: https://lafeber.com/vet/anesthetic-depth-in-exotic-animals-monitoring-the-degree-of-central-nervous-system-depression/#reptilereflexes.

 

2016 Expert Q&A

Although many chatbox questions were answered during the live 2016 webinar session, the remaining questions were answered by email and are summarized below:

General principles Inhalant anesthesia Injections
Signs of pain Monitoring Miscellaneous
Preoperative period Catheters and fluids References
Agents and/or routes Venipuncture

GENERAL PRINCIPLES

Q: Do external temperature fluctuations significantly affect drug metabolism?
A: YES. There’s definitely going to be an effect with temperature. The closer the reptile is to its preferred optimum temperature zone for the species, the more efficiently they will metabolize drugs and they will also get rid of the anesthetic drugs more efficiently so that will also help with recovery of the animals.

 

Q: What is the mortality rate associated with anesthesia in reptiles?
A: I am not aware of any studies in the literature that document what the mortality rate is per se. Of course it’s going to depend on the health status of the animal, the type of procedure, etc. I would say in general, compared to mammals or birds, the mortality rate is probably going to be a little bit less in reptiles. We don’t see as many mortalities, but you WILL see a lot more prolonged recoveries.

 

SIGNS OF PAIN

Q: Is there any correlation between pain and leg use in chelonians with midline carapacial injuries?

A: That’s a really good question. I don’t know about correlation between pain and leg use, but one thing we know about reptiles is they tend to have a lot of peripheral innervation that is independent of central innervation. Although more research is needed, the short answer to that question is: There are no studies that I’m aware of that show a particular correlation between pain and leg use.

We have seen chelonians that have mid-carapacial injuries or even complete, transverse, spinal injuries—with no connection whatsoever—and they’re still able to move their limbs. The reptile nervous system is very different. There’s a whole different pathway here, a lot more peripheral pathways. You certainly will see animals that might have decreased use of those limbs, but whether that’s from the nervous injury itself or pain, that’s hard to tell.

 

PREOPERATIVE PERIOD

Q: So are you not as concerned about doing bloodwork in older reptile patients prior to giving an NSAID like we often do for mammals?

A: In general, exotics seem to be a lot more tolerant to NSAIDs and don’t get as many of the side effects as in mammals. That is evidenced also by the higher dosages that we use in exotic species. Of course having bloodwork is always ideal. If you can have that bloodwork, especially a biochemistry panel, that is always going to be good.

Hydration status is also a consideration. So we are always get concerned about patients that are very dehydrated while using NSAIDs. Give fluids concurrently with NSAID administration. It’s definitely something to monitor, but reptiles definitely aren’t as sensitive to the side effects of NSAIDs as dogs and cats.

 

Q: How long should you fast reptiles?

A: This will depend on the species. We typically do a few (2-3) hour fast. One big advantage of reptiles is that the clinician can have much better control of the glottis, so aspiration pneumonia is a lot less likely to happen compared to a bird. But again it depends on the species and what they’re eating. Obviously it’s based on the metabolism; that’s going to change quite a bit too.

Most reptiles you can really just fast them for a day or two before the procedure. There are only rare instances when you’re going to have reptiles that are constantly eating like a dog or cat or other mammals. So fasting is typically not that big of a concern.

Clinically, it’s not something we think about other than making sure that if we have a snake, for example, don’t feed them the day before. If we have some of the chelonians, they do tend to eat a little bit more constantly, we’ll typically pull the food 2-3 hours before the procedure.

 

Q: Is preoperative oxygen therapy contraindicated as well?

A: That’s a good question. I don’t know that preoxygenation is CONTRAINDICATED but I don’t think that anyone has done any studies to look at the benefit of preoxygenation in reptiles as in other species. I don’t think you’re necessarily going to see a significant detrimental effect for anesthesia, but you do have to keep in mind that if you preoxygenate, the reptile will probably become apneic a lot sooner but most reptiles under anesthesia will become apneic anyway and you’ll just have to begin intermittent positive pressure ventilation regardless.

So I don’t think it’s necessarily a bad idea, but there’s just not enough information about how helpful it is. It’s something clinicians can try. I think preoxygenation would be more of a consideration if the reptile has respiratory disease and the ability to move oxygen may be altered in any way, shape, or form. Or preoxygenation might be a consideration for anemic animals. In animals that don’t suffer from these conditions, it might be hard to tell how beneficial preoxygenation might be.

 

SPECIFIC AGENTS AND/OR ROUTE OF ADMINISTRATION

Q: Do you inject alfaxalone all at the same site? Because volume is usually pretty high for large animals.

A: It depends on the volume and the size of the animal. In larger animals, alfaxalone does come to a large volume, so sometimes you need to split it between multiple sites if you’re going IM but if you’re going intravenously you can give it intravenously in the full volume.

Q: Do you use a new bottle of alfaxalone every time, how long do you store it. We have very variable effectiveness.

A: At least in the United States, alfaxalone is labeled for single use, so you do have to discard the bottle after you use it. So we [LSU-SVM] don’t store it. The bottle is opened up, and it has to be discarded that same day.

So if someone is looking at effectiveness after storage, then they need to look at the formulation depending on what country they’re in. I’m not sure if any formulations from other countries can be kept longer or not.

Q: What is the CRI dose of alfaxalone?

A: No real research has been done with CRI on alfaxalone; there are no good doses available in the literature at this time. Alfaxalone was mentioned because it is certainly a drug that CAN be used because alfaxalone is not going to accumulate in the system; it will be metabolized and excreted a lot faster.

If you look at dog and cat medicine, for example, and we extrapolate from their dosing system: Induction for a dog will be about 1-3 mg/kg and then for a CRI they will do 4-7 mg/kg, so basically they’re doubling the dose. In the reptile, there’s really a wide range of doses for alfaxalone, anywhere from 5-20, or even 30 mg/kg, depending on the species. So if someone wanted to attempt an alfaxalone CRI, I would probably start at 5-10 mg/kg, see what you get, then bump up from there.

 

Q: Any info on butorphanol?

A: For a number of years now, butorphanol has not been selected for analgesia in reptiles and that’s because butorphanol mostly affects kappa receptors and reptiles are now found to have more mu receptors. So that’s why the trend has been over the years to go away from butorphanol and start using drugs like morphine and hydromorphone.

In the presentation, I did not mention the drugs that are not used anymore, that don’t work in reptiles. I strictly described the drugs that are currently recommended and that are being used. So butorphanol is certainly not something that we recommend any more for analgesia whatsoever. I realize in some parts of the world, like Latin America, there is easy access to butorphanol but not so much to the other opioids. So you could still potentially use butorphanol as a sedative or as part of your anesthetic protocol, but it’s not going to necessarily provide analgesia. So in those instances, you’re going to have to rely more on meloxicam, or tramadol potentially.

Q: Are you using butorphanol or methadone in reptiles for sedation or premedication?

A: We don’t really use butorphanol in reptiles anymore because the main reason for the use of butorphanol in the past was as an analgesic, and now we know that reptiles are more receptive to mu-opioid agonists, not the kappa. You can certainly use butorphanol as an anesthetic or sedative, however the effectiveness of butorphanol as a sedative compared to hydromorphone is difficult to evaluation in reptiles, so we really don’t use butorphanol anymore in reptiles.

With regards to methadone, there is no good data on methadone use in reptiles yet.

 

Q: Any research into the use of desflurane?

A: I have no information on desflurane. I think isoflurane and sevoflurane are prevalent in veterinary medicine, and inexpensive enough. I think desflurane gets significantly more expensive, however desflurane would work. I don’t see any reason why it would not.

 

Q: What was the ketamine and dexmedetomidine dose?

A: I always encourage people to refer back to the literature. There are plenty of formularies out there. There’s the Exotic Animal Formulary, there’s a number of different textbooks that formularies in them. So it’s always best to go back.

Ketamine-dexmedetomidine doses are also going to vary with the species, the health status of the patient, the procedure. So make those educated determinations based on what you find in the formularies and based on the assessment of your patient.

Editor’s note: The doses mentioned in Dr. Nevarez’s presentation were ketamine (2-5 mg/kg) dexmedetomidine (0.025-0.05 mg/kg)

I am also interested in the use of the fentanyl patch, but I don’t understand if the dose was 2.5 – 12.5 μg/reptile/h or μg/kg/h.

A: In slide 12 of Dr. Nevarez’s presentation, the dose is written as 2.5-12.5 μg/h q24-72h (Gutwillig et al 2012, Darrow et al 2010, Gamble 2008)

 

Q: Is there any benefit to giving hydromorphone PO for analgesia?


A: The problem with oral administration, is we don’t necessarily have pharmacokinetic (PK) information, so I recommend before using any drug: Go online, try to find papers in the literature, see if there are any PK studies out there and then try to extrapolate. Based on that, making the best educated decision that we can. This is something we do on a daily basis when deciding on the use of some drugs. Another thing to add about oral administration in reptiles is you have to make sure the patient is healthy enough that the gut is working properly. And snakes are a very big challenge because adults usually eat once a week or every other week, so giving a lot of oral medication on a daily basis is probably not going to have significant absorption. So whenever possible, stay away from oral administration. Before giving any drugs orally to a reptile, you have to make sure that they are at the proper temperature, that metabolism is working properly to ensure they’re actually maximizing absorption of the drug.

 

Q: Can meloxicam be administered to reptiles orally?

A: I think a lot of people have to give meloxicam orally for outpatient care, but whenever possible, give an injectable. This will be a lot better than the oral route.

 

Q: What about medetomidine?

A: Medetomidine is certainly something we used to use. We don’t have medetomidine easily available in the States anymore, that’s why everyone has switched over to dexmedetomidine, but yes, if you have medetomidine available, it is something that was used very successfully in reptiles for a long time. So that’s certainly an option as part of a balanced anesthetic protocol.

 

Q: Do you combine midazolam with butorphanol?

A: We use midazolam a lot, [but] we don’t really use butorphanol in reptiles anymore because the main reason for the use of butorphanol in the past was as an analgesic, and now we know that reptiles are more receptive to mu-opioid agonists, not the kappa. You can certainly use butorphanol as an anesthetic or sedative., The effectiveness of butorphanol as a sedative compared to hydromorphone is hard to tell, so we really don’t use butorphanol anymore in reptiles. Midazolam typically goes with hydromorphone or morphine.

 

Q: Can you do constant rate infusion (CRI) of propofol?

A: Yes, you can certainly do a CRI of propofol. I think the one thing to really be careful of is propofol can stay around in the system a lot longer than [something like] alfaxalone.

Editor’s Note: A maintenance range of 0.3–0.5 mg/kg/min IV has been described in the literature.

 

Q: Tiletamine use?

A: Telazol can certainly be used and there are still some species out there in which people use it. I think with the combinations of ketamine-dexmedetomidine-midazolam in which you can provide more balanced anesthesia, single use of Telazol has fallen out of favor. There are doses for tiletamine out there, you have to go back to the formularies, but again tiletamine by itself is not going to be adequate for true, balanced anesthesia, so I would obviously add some other compounds to that.

 

Q: Do you use tramadol orally?

A: We routinely do not use tramadol, but…if you talk to a small animal anesthesiologist, they’re not necessarily big fans of tramadol. They don’t really feel it has that great of an effect.

 

Q: If you have surgical patients that are very painful, post op meds? Meloxicam and re-dose hydromorphone?
A: Yes, for post-op meds yeah we’ll use meloxicam, then re-dose hydromorphone. Probably no more than q12h with the hydromorphone, so every 12-24 hours. It is very important to monitor the patient, then assess for pain and discomfort, then re-dose as the veterinarian deems appropriate. One thing to be careful of with more frequent dosing of hydromorphone is to look for evidence of sedation, which can also happen.

 

Q: What do you recommend for long-term pain relief for reptiles?

A: That’s an area where more research needs to be done, but based on the current research mu-opioid agonists are going to be more effective so they’re certainly an option.

We also use a lot of meloxicam, although there’s a lot of concern about its true effectiveness, but that’s why I typically use a dose of 0.5-1.0 mg/kg. Most of the studies are using the lower dosages in the 0.2 mg/kg range. Sometimes I’ll put reptiles on 1 mg/kg for a few days, then bring them down to 0.5 mg/kg. Clinically, I think it does seem to make a difference but again research is needed to look at the actual effectiveness of these higher dosages.

So again we sometimes use a combination of both non-steroidals and opioids for long-term pain relief.

 

Q: What doses of these drugs for intrathecal administration?
A: That is very well described in the paper cited in the presentation. Those interested in more information can go to the article. It explains the procedure and provides the dosages there.

Lidocaine (4 mg/kg, 2%), bupivacaine (1 mg/kg, 0.5%) and morphine (0.1-0.2 mg/kg) were used to provide spinal analgesia in male red-eared sliders over 0.5 kg BW (Mans 2014)

 

Q: How to give oral analgesic to snakes for long periods?
A: Again oral administration is not the most efficient route because the gut is not working when the reptile is not digesting prey items. So absorption is not going to be very efficient. We certainly have seen snakes that we’ve had on oral antibiotics long term and they certainly do seem to improve on that, but one trick when you’re doing that is, in addition to giving the oral analgesic like meloxicam, give a little bolus of fluid in an effort to stimulate gut motility, but again there’s no real data out there on that.

 

Q: When using your combinations are you mixing all into one syringe or giving the different drugs at intervals?
A: It depends on which drugs you’re using, the volume, the purpose. When we’re doing combos of ketamine, dexmedetomidine, hydromorphone, and midazolam in a large reptile, like a crocodilian or large sulcate for example, often I will put all that in one syringe and give that all IV. If you have a smaller patient and you have to go intramuscular, sometimes you do have to split that a little bit more. And in that case, I would probably give the hydromorphone and midazolam as a premedication IM first in one site. And then come back with the ketamine-dexmedetomidine in a different site.

 

INHALANT ANESTHESIA

Q: Do you have to mechanically ventilate all reptiles under general anesthesia?
A: Yes, a lot of reptiles will become apneic under general anesthesia and much of that probably has to do with the 100% oxygen flow, so you either have to manually ventilate them or put them on a mechanical ventilator, depending on patient size. For most reptiles, you only have to ventilate them 2-4 times per minute, depending on the species, size, etc.

 

Q: How long do you have from discontinuation of oxygen to movement/recovery of the patient?

A: That is going to depend on your anesthetic protocol, and assuming the patient is warm, well hydrated, and all the other things that we talked about.

If you’re using something like alfaxalone-midazolam-hydromorphone, for example, those animals typically recover fairly quickly. If you’re using a combination of ketamine-dexmedetomidine-hydromorphone-midazolam, they’ll be a little bit more of a lag but it depends on the duration of the procedure. With any of those combinations you’re typically get a good 30-45 minutes just on injectables, that’s not adding gas anesthetic. So in my experience, if you discontinue oxygen as soon as you start closing the incision when doing a coelomic surgery, by the time you’re done with that incision—I’d say within 20-30 minutes of discontinuing oxygen and gas—you should start seeing some movement from the patient and early signs of recovery. And for sure within an hour, you should start seeing that animal recover back. So typically within 30 minutes to an hour, the animal should be either fully recovered or significantly recovered.

 

MONITORING

Q: How to do corneal reflex in patient with spectacles?
A: The corneal reflex is not an option in species with spectacles, like snakes, for monitoring anesthesia.

 

Q: What brand of temperature monitor do you use for esophageal monitoring?

A: As far as brand of temperature monitor, it really doesn’t matter. You can use whatever brand you have available to you. We [LSU-SVM] typically use temperature probes that are attached to our anesthetic monitoring equipment. There are also temperature probes that can be attached to pulse oximeters, so there are a wide, wide range of monitors [available].

We’re [LSU-SVM] now working on a study comparing esophageal versus cloacal temperatures. One important thing we found is that some of the flexible probes will actually break down and go bad over time. So you have to make sure you are using probes that are working properly. We found that some probes were reading even a 2-3-degree difference. So upkeep of those probes is going to be important.

 

CATHETER PLACEMENT & FLUID THERAPY

Q: Where would you recommend placing an intravenous (IV) cannula if required during surgical procedures?
A: Visit Administration of Medication in Reptiles for a list reptile IV catheter sites that do not require a cutdown. Additional advice on catheter placement can be found in the brief article: Catheters in Reptiles.

 

Q: With intraosseous (IO) how much slower does the infusion need to be compared to IV? (e.g. for constant rate infusions and intravenous fluid therapy)

A: The infusion rate will vary quite a bit with the size of the animal, the size of their bones, the location of the needle. If you have an intraosseous catheter needle that’s too close to the middle of the bone, where you have more of the fat tissue within the medullary cavity, the absorption is going to be slower.

What I typically do is, I will go for a maintenance rate of about 10-30 ml/kg/day. Typically, I’ll start reptiles at about 10 ml/kg/day. So when I start an IO catheter, is I start them at half that rate, monitor the patient, make sure we’re not getting any leakage, and then slowly bump up the rate from there if you’re not getting any leakage. If your rate is too high, often what will happen, even if the catheter is seated correctly, you’ll start getting either leakage at the insertion point of the catheter or sometime through some of the nutrient foramina of the bone, and you’ll start getting some edema around the bone, so that will be an indication to slow down the rate.

 

Q: Is there a need for special follow-up care if using IO catheters? Do you use those only in surgery or in intensive care patients also?
A: A simple wrap using elastic bandage material and cotton or gauze is sufficient. Also, yes, an intraosseous catheter can definitely be used in an intensive care setting.

 

Q: What is a fluid rate for reptiles per hour?
A: I typically don’t think of fluid therapy on a per hour basis; I’m always treating my patients for their maintenance needs over a 24-hour basis. So you can just figure out the math using 10-30 ml/kg/day (or 0.42-1.25 ml/kg/hr) depending on species, hydration status, then adding replacement deficits as needed, but the standard is 10-30 ml/kg/day. If the patient is severely dehydrated, shock, etc., this rate can be adjusted to give a 5 ml/kg bolus. Clinical judgement is still needed to determine the best approach for a particular patient.

 

Q: Do you have preferred fluid replacement guidelines/amounts for chelonians?

A: Maintenance requirements for reptiles are estimated as 10-30 ml/kg/day, however chelonians do tend to get overhydrated a little bit faster, and a little bit easier than other reptiles so I tend to stay at the lower end of 10-20 ml/kg/day for chelonians. I don’t typically use 30 ml/kg.

Sometimes when people are using intracoelomic (IC) fluids, chelonians don’t absorb these fluids as well and will retain some of these fluids a bit longer. Some people will elect to make a dilution of fluids using a 1:1 mixture of lactated Ringer’s (or NormosolTM or PlasmaLyte®) with saline to try to reduce the osmolality of the fluid, making it more hypotonic. So the fluids can be absorbed into the body a bit faster.

Osmolality plays an important role. There are a number of studies looking at osmolality, especially in chelonians in which plasma osmolality changes significantly across species, health status, etc. Currently, we don’t have very good formulas to calculate the osmolality of every chelonian species. If the osmolality was known, then you could match the fluids to the osmolality and route. If you’re giving fluids intravenously, intraosseously or subcutaneously, you just want to go with isotonic fluids. But if you’re going intracoelomic, there’s still potentially an argument that you want to go with hypotonic fluids to try to make sure those fluids get pulled into the vascular system and they don’t just hang around in the coelomic cavity.

 

Venipuncture

Q: How much blood can we be comfortable in removing in relationship to body size?

A:

  • Blood volume is estimated to be approximately 10% of body weight in grams. The actual amount will vary by species (and individual) of course.
  • In a health specimen, approximately 10% of blood volume or 1% of body weight (BW) can be collected. One person wrote 0.8% and that is actually a good rule of thumb because you want to have a “buffer zone” for inadvertent patient bleeding or bruising after venipuncture. So for instance, in an 80-gram gecko, a maximum of 0.8 ml could be collected however ~0.64 would be a more prudent volume.
  • In a debilitated and/or anemic patient, collection of a maximum of 0.05% of BW is recommended.

 

Q: Anybody have pictures of brachial venipuncture?
A (2016): Unfortunately LafeberVet does not have photos available at this time. We can refer you to an excellent article by Dr. Christoph Mans, which includes brachial venipuncture photos: Venipuncture Techniques in Chelonian Species.

Editor’s Note (2023): Please visit LafeberVet’s Reptile Venipuncture Teaching Module, which includes information on brachial venipuncture in chelonians.

 

INJECTIONS

Q: What is the preferred intramuscular injection site in chelonians?
A: The forelimbs are the preferred site for intramuscular injections in turtles and tortoises. Go to Administration of Medication in Reptiles for a brief video that illustrates recommended injection techniques.

 

MISCELLANEOUS

Q: What is your email address Dr. Nevarez?

A: jnevare@lsu.edu

 

Q: Would love the rest of your drug dosages! (anesthetic protocols)

A: I did put some doses in my presentation, but all of the doses we use come straight from the formularies or textbooks. Doses will also vary with the species and the procedure, so it’s very difficult to give one drug dose across the board because it’s going to vary quite a bit. We use the Carpenter’s Exotic Animal Formulary a lot, as well as Current Therapy in Reptile Medicine and Surgery and Reptile Medicine and Surgery. Most of the big reptile books are going to have a formulary in the back.

 

RACE approval

This 2024 program was reviewed and approved by the American Association of Veterinary State Boards (AAVSB) Registry of Approved Continuing Education (RACE) program for 1 hour of continuing education in jurisdictions that recognize AAVSB RACE approval.

 

References

References

References listed below were discussed during the 2024 presentation or touched upon during the Q&A session:

  1. Ferreira TH, Fink DM, Mans C. Evaluation of neuraxial administration of bupivacaine in bearded dragons (Pogona vitticeps). Vet Anaesth Analg. 2021;48(5):798-803. doi: 10.1016/j.vaa.2021.06.012. Epub 2021 Jul 2. PMID: 34326001.
  2. Ferreira TH, Mans C. Evaluation of neuraxial anesthesia in bearded dragons (Pogona vitticeps). Vet Anaesth Analg. 2019 Jan;46(1):126-134. doi: 10.1016/j.vaa.2018.09.001. Epub 2018 Sep 19. PMID: 30344028.
  3. Fink DM, Ferreira TH, Mans C. Neuraxial administration of morphine combined with lidocaine induces regional antinociception in inland bearded dragons (Pogona vitticeps). Am J Vet Res. 2021;83(3):212-217. doi: 10.2460/ajvr.21.08.0104. PMID: 34968185.
  4. Galli G, Taylor EW, Wang T. The cardiovascular responses of the freshwater turtle Trachemys scripta to warming and cooling. J Exp Biol. 2004;207(Pt 9):1471-8. doi: 10.1242/jeb.00912. PMID: 15037641.
  5. Greunz EM, Williams C, Ringgaard S, et al. Elimination of intracardiac shunting provides stable gas anesthesia in tortoises. Sci Rep. 2018;8(1):17124. doi: 10.1038/s41598-018-35588-w. PMID: 30459408; PMCID: PMC6244002.
  6. Hicks JW. Adrenergic and cholinergic regulation of intracardiac shunting. Physiological Zoology. 1994;67(6):1325-1346. https://doi.org/10.1086/physzool.67.6.30163900.
  7. Kharbush RJ, Gutwillig A, Hartzler KE, et al. Antinociceptive and respiratory effects following application of transdermal fentanyl patches and assessment of brain μ-opioid receptor mRNA expression in ball pythons. Am J Vet Res. 2017;78(7):785-795. doi: 10.2460/ajvr.78.7.785. PMID: 28650234; PMCID: PMC5584939.
  8. Kristensen L, Zardo JQ, Hansen SM, et al. Effect of atropine and propofol on the minimum anaesthetic concentration of isoflurane in the freshwater turtle Trachemys scripta (yellow-bellied slider). Vet Anaesth Analg. 2023;50(2):180-187. doi: 10.1016/j.vaa.2021.10.008. Epub 2022 Nov 30. PMID: 36739261.
  9. Mans C. Clinical technique: intrathecal drug administration in turtles and tortoises. J Exotic Pet Med. 2014; 23(1):  67-70. doi:  10.1053/j.jepm.2013.11.011.
  10. Mans C, Steagall PVM, Lahner LL, Johnson SM, Sladky KK. Efficacy of intrathecal lidocaine, bupivacaine, and morphine for spinal anesthesia and analgesia in red-eared slider turtles (Trachemys scripta elegans). Proc Annu Conf American Association of Zoo Veterinarians. 2011. P. 135. Available at https://www.researchgate.net/profile/Christoph-Mans/publication/292020716_Efficacy_of_intrathecal_lidocaine_bupivacaine_and_morphine_for_spinal_anesthesia_and_analgesia_in_red-eared_slider_turtles_Trachemys_scripta_elegans/links/56ad2d5708aeaa696f2cadb8/Efficacy-of-intrathecal-lidocaine-bupivacaine-and-morphine-for-spinal-anesthesia-and-analgesia-in-red-eared-slider-turtles-Trachemys-scripta-elegans.pdf.
  11. Perry SM, Nevarez JG. Pain and its control in reptiles. Vet Clin North Am Exot Anim Pract. 2018;21(1):1-16. doi: 10.1016/j.cvex.2017.08.001. PMID: 29146025.
  12. Sadler RA, Schumacher JP, Rathore K, et al. Evaluation of the role of the cyclooxygenase signaling pathway during inflammation in skin and muscle tissues of ball pythons (Python regius). Am J Vet Res. 2016;77(5):487-94. doi: 10.2460/ajvr.77.5.487. PMID: 27111016.
  13. Schumacher J, Yelen T. Anesthesia and analgesia. In: Mader D (ed). Reptile Medicine and Surgery, 2nd ed. 2012. St. Louis: Saunders Elsevier. Pp 442-452.
  14. Sladky KK. Treatment of pain in reptiles. Vet Clin North Am Exot Anim Pract. 2023;26(1):43-64. doi: 10.1016/j.cvex.2022.07.004. PMID: 36402488.
  15. Sladky KK, Mans C. Clinical anesthesia in reptiles. J Exotic Pet Med. 2012;21(1):17-31. doi:  10.1053/j.jepm.2011.11.013.
  16. Ting AKY, Tay VSY, Chng HT, Xie S. A critical review on the pharmacodynamics and pharmacokinetics of non-steroidal anti-inflammatory drugs and opioid drugs used in reptiles. Vet Anim Sci. 2022;17:100267. doi: 10.1016/j.vas.2022.100267. PMID: 36043206; PMCID: PMC9420515.
  17. Walter B, Johnson S, Sladky K, Cox S, Thurber M. Serum fentanyl concentrations and behavior associated with transdermal fentanyl application on healthy corn snakes (Pantherophis guttatus). J Zoo Wildl Med. 2024;54(4):738-745. doi: 10.1638/2022-0162. PMID: 38251997.

 

FURTHER READING

Darrow BG, Myers GE, Kukanich B. Fentanyl transdermal therapeutic system pharmacokinetic in ball pythons (Python regius). Proc Annu Conf Am Assoc Zoo Vet 2010:238-239.

Gamble KC. Plasma fentanyl concentrations achieved after transdermal fentanyl patch application in prehensile-tailed skinks, Corucia zebra. Journal of Herpetologial Medicine and Surgery. 2008; 18(3/4):81-85. doi:  10.5818/1529-9651.18.3-4.81.

Gutwillig A, Abbott A, Johnson SM, et al. Opioid-dependent analgesia in ball pythons (Python regius) and corn snakes (Elaphe guttata). Proc Annu Conf Assoc Reptile Amphibian Vets 2012:66.

Rivera S, Divers SJ, Knafo SE, et al. Sterilisation of hybrid Galapagos tortoises (Geochelone nigra) for island restoration. Part 2: phallectomy of males under intrathecal anaesthesia with lidocaine. Vet Rec. 2011;168(3):78. doi: 10.1136/vr.c6361. Epub 2011 Jan 17. PMID: 21257586.

To cite this page:

Nevarez J. Spotlight on anesthesia and analgesia in reptiles. Aug 4, 2016; updated January 28, 2024. LafeberVet website. Available at https://lafeber.com/vet/spotlight-anesthesia-analgesia-reptiles/