Anesthesia and Analgesia

 

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Module Goals

  • Compare and contrast chelonian vs. small animal anesthesia and analgesia
  • Know which anesthetic and analgesic drugs are commonly used by TRT
  • Identify important resources that can be used to develop drug protocols in turtles

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Introduction

The general principles of anesthesia and analgesia are the same in turtles as they are in domestic species. The goals are to reduce pain and discomfort for the patient during a procedure while making sure that oxygen and glucose can get to all the tissues that need it. All patients should receive pre-anesthetic exams to ensure that they are healthy enough to be anesthetized, and they should be monitored during anesthesia. That being said, there are some unique anatomical considerations that must be kept in mind when anesthetizing turtles, discussed below. Additionally, the use of anesthetic and analgesic drugs in the turtle species we see in NC is largely extrapolated from other species, with only a few resources available as guides.

Anesthesia

Unique anatomical and physiological considerations

For additional details on the unique anatomy and physiology of turtles, please refer to the Anatomy and Physiology section.

  1. Turtles do not autoregulate their body temperature and they must be maintained within their preferred optical temperature zone (POTZ) during anesthesia. Room temperature is generally adequate for turtles, but during and after surgery they should not be allowed to get cold as this will interfere with healing. Temperature can also impact the metabolism of some drugs, and in the literature you may find that researchers investigate pharmacokinetics at multiple temperatures in reptiles.
  2. Aquatic turtles, and box turtles to a lesser extent, utilize an intracardiac right-to-left shunt to maximize oxygen and perfusion during periods of apnea (i.e., diving, or anesthesia). This means turtles are fairly hypoxia tolerant, but it also means that they will not metabolize inhaled drugs in a consistent manner. Changes in the shunting pattern can also result in rapid changes in anesthetic depth if using inhalants. Furthermore, you may find that aquatic turtles will hold their breath for a long time, requiring patience during intubation.
    Illustration of the intracardiac right-to-left shunt in reptiles. PA: Pulmonary artery. LAo: Left aortic arch. RAo: Right aortic arch. RAt: Right atrium. LAt: Left atrium. Source: Hicks and Wang 2012.
  3. Whenever possible, injectable drugs should be given in the front half of the body to avoid the hepatic first-pass effects of the renal portal system.

    The renal portal system of reptiles. Injections given in the caudal half of the body may be metabolized or excreted by the kidneys prior to distribution to the body. Source: Holz et al 1998.
  4. While elevated carbon dioxide is the driver of respiration in mammals, turtles are driven to respire due to low oxygen. For this reason, 100% oxygen is not recommended in turtles (at least during the recovery period) as it suppresses respiration. Ambu-bags are sufficient.
  5. Turtles lack a diaphragm and use their skeletal muscles to facilitate exhalation. Turtles that are fully anesthetized will therefore require intermittent positive pressure ventilation, as they will not be able to voluntarily move on their own.

    An Ambu-bag is used to provide ventilation to an intubated turtle.
  6. Intubation can be accomplished through the glottis, which is located caudal to the base of the tongue. Turtles have complete tracheal rings and the tracheal bifurcation is cranially positioned, so non-cuffed endotracheal tubes should be used and inserted gently.
The endotracheal tube is inserted into the glottis at the base of the tongue.

Anesthetic drugs commonly used by the Turtle Rescue Team

At the Turtle Rescue Team, we often have to rely on whatever drugs are available to us. The drugs we commonly use for anesthesia and analgesia are listed below – but there are many more drugs that can be used in turtles. Please refer to the book chapter from the Exotic Animal Formulary listed in the “Additional Resources” for information about drugs you have available in your practice that are not listed here.

Drug/Name Class Dose and Route Notes
Alfaxalone (Alfaxan) Neuroactive steroid, General anesthetic 5-10 mg/kg IV, IM, or SC Can cause respiratory depression. Use SC route for large volumes.
Ketamine (Ketaset) NMDA receptor antagonist, Dissociative 5-10 mg/kg IM Prolonged recovery if used alone and at high doses, usually combined with an alpha-2 agonist or benzodiazepine.
Dexmedetomidine (Dexdomitor) a2-adrenergic receptor agonist 0.05-2 mg/kg IM or IV Also analgesic. Often combined with ketamine.
Atipamezole (Antisedan) Reversal agent 0.05-2 mg/kg IM Used to reverse dexmedetomidine.
Propofol (Diprivan) Non-barbiturate general anesthetic 3-10 mg/kg IV Profound respiratory depression can occur.
Morphine Mu-opioid 0.5 mg/kg IM Can result in respiratory depression. Often used with ketamine + dexmedetomidine.
Tiletamine + Zolazepam (Telazol) Dissociative anesthetic and benzodiazepine 4-8 mg/kg IM
Lidocaine Local anesthetic 5-10 mg/kg Line block or nerve block
Bupivacaine Local anesthetic 1-2 mg/kg Line block or nerve block

Table 1. Common anesthetic drugs used in the Turtle Rescue Team.

Anesthetic Monitoring

Monitoring is a crucial component of anesthesia for any species, but very few validated monitoring methods exist for reptiles. You can adapt your monitoring protocols based on the equipment you have available in your practice. Normal values in reptiles are difficult to characterize due to the influence of ambient temperature on turtle respiration, heart rate, and body temperature. Values given below are representative of what can be expected from most reptiles during an anesthetic event.

The heart rate can be measured using a doppler – pencil probes are the easiest to use. The probe should be positioned between the neck and the proximal humerus and pressed gently in the medial direction. The heartbeat can be heard from either side of the turtle. Heart rates vary considerably depending on the turtle and the ambient conditions, but a HR of 20-50 can be considered normal for most turtles. A good rule is to assess the patient’s anesthetic heart rate in relation to its pre-anesthetic heart rate.

The heart rate is being measured with a doppler probe between the neck and shoulder, using a plunger to subdue the snapper’s dangerous head.

Respiratory rate can be difficult to determine in turtles, especially under anesthesia. Respirations are counted by visually observing the turtle breathing – often, you can see the limbs moving slightly in and out to facilitate exhalation. During anesthesia, the turtle will likely be intubated and receiving manual ventilation using an ambu-bag. A good respiratory rate for manual ventilation is 3-5 breaths per minute at <12 cm H2O pressure.

Core body temperature can be measured using a probe via the cloaca. The turtle should be within its POTZ – usually around 70 degrees Fahrenheit or 21 degrees Celsius.

Exhaled CO2 can be measured using a capnometer on an intubated turtle, similar to in small animals. EtCO2 should be maintained between 10-25 mmHg. Due to the right-to-left shunt in turtles, it is difficult to interpret EtCO2 as a function of metabolic acid-base status.

An ECG can be used for monitoring heart rhythm and electrical activity in turtles. Standard placement of leads on the right and left forelimbs and left hindlimb are used and lead II can be read similar to in mammals. Leads can also be clipped to the marginal scutes dorsal to the appropriate limbs for each lead. There is very little information available on interpretation of reptilian ECG, and this method cannot be used to confirm death as the heart will continue to produce electrical signals post-mortem.

ECG leads on a red-eared slider. Source: Mans et al. 2019.

Common reflexes measured in turtles for anesthesia monitoring include palpebral, withdrawal, and jaw tone. Generally, the hind limb withdrawal reflexes are the last reflexes to disappear and the first ones to return. Jaw tone is an excellent indicator of the appropriate time to intubate or extubate.

If fluids are given during a surgical procedure, the recommended infusion rate for reptiles is 3 mg/kg/hr. Lactated Ringer’s Solution is used most frequently.

There are no validated methods for measuring blood pressure or pulse oximetry in turtles. While arterial blood gases are theoretically possible to measure, it is very difficult to find an artery in most of the species that we work with.

Anesthetic Recovery

Recovery times in turtles can be significantly longer than those in mammals as they do not metabolize anesthetic drugs as quickly. The use of a multimodal drug protocol in which one or more of the drugs is reversible can help shorten recovery times, and keeping the turtle within its POTZ is also critical. Manual ventilation with an Ambubag facilitates recovery, as well.Reflexes and muscle tone can be used to determine the status of recovery. Once a turtle is biting on the endotracheal tube (which should be protected), it is safe to extubate the turtle. The turtle may continue to be drowsy or lethargic for several hours following anesthesia, depending on the drug protocol used.

Analgesia

Measuring pain in turtles can be challenging. A validated “turtle pain scale” does not currently exist. Some turtles with severe pain may become lethargic or even depressed, and sometimes they will close their eyes. Other turtles will show no signs of pain at all, or pain can be hidden by the stress of hospitalization. Anorexia can be a sign of pain in turtles, but they will often refuse to eat in captivity whether they are in pain or not, so this is not a consistent indicator of pain.When turtles present to your clinic for traumatic injuries, it is safe to assume that they are feeling pain and analgesic therapy should be provided. Turtles with viral infections or aural abscesses may or may not be painful on presentation. Typically, turtles with aural abscesses are given mild analgesic drugs perioperatively, and viral turtles are given anti-inflammatory eye-drops.

Analgesic drugs commonly used by the Turtle Rescue Team

A table of the drugs we use most frequently in the Turtle Rescue Team is provided below. As with the anesthetic drugs, please refer to the resources below for more information about drugs you have available in your practice.

Drug/Name Class Dose and Route Notes
Ketoprofen (Ketaset) NSAID 2 mg/kg IM For mild pain
Ketorolac (Toradol) NSAID 0.25 mg/kg IM For moderate pain
Morphine Mu-opioid 1.5 mg/kg IM For severe pain

Table 2. Common analgesic drugs used in the Turtle Rescue Team.For turtles with traumatic injuries, we typically start them on ketorolac for 3 days, followed by ketoprofen every other day for up to 2 weeks. Turtles with injuries that are minor or that just have some inflammation can start on ketoprofen rather than ketorolac. As with NSAID use in all animals, turtles must not be allowed to become dehydrated during NSAID therapy.Morphine is reserved for turtles in very severe pain, or for use perioperatively for more invasive procedures such as an amputation. Additionally, morphine is a good analgesic option for turtles that are very active but need some sedation to prevent the perpetuation of an injury. Morphine can cause respiratory depression in turtles, so patients receiving morphine should be monitored.

Relevant Videos

Endotracheal Intubation

Additional Resources

Key Concepts

  • Turtles have unique anatomical and physiological traits that must be considered when designing anesthesia protocols.
  • Many of the anesthesia and analgesia drugs that are used in small animal medicine are also used in turtles. Multimodal anesthesia with reversible drugs is preferrable, and several resources are available for determining doses (Carpenter 2019, Mans et al 2019, Sladky and Mans 2019).
  • Very few monitoring methods have been validated for reptiles, and any monitoring modality must be interpreted in light of the individual patient.
  • Analgesia should be provided to any turtle with a traumatic injury.

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