Marine Mammal Restraint & Anesthesia

Question 1

What drug has been used for smooth, reliable IV induction of general anesthesia in cetaceans?

Answer 1

Propofol (West)

Question 2

What is the inhalational anesthetic of choice for cetaceans?

Answer 2

Isoflurane (West)

Question 3

What is the dive response that occurs in marine mammals?

Answer 3

Intro

• The dive response is a series of neurally mediated physiological adaptation designed to conserve endogenous oxygen stores during diving
• The response is shared in all mammals tested thus far, but is most well studies in marine mammals, reptiles, and aquatic birds
• Highly powerful autonomic response consisting of bradycardia, decreased cardiac output, peripheral vasoconstriction with maintenance of increase of central arterial BP
• Dive response can be triggered by other stimuli (including anesthesia)

Question 4

Describe the effects of the dive response on cardiac output.

How low can the heart rate get?

How does stroke volume change?

How does heart rate change as animals surface?

Answer 4

Bradycardia and Cardiac Output (CO)

• Bradycardia can be as low as 1/10 or less of surface heart rates
  
  • However, these forced submersion studies have mostly been done in pinnipeds, less info in cetaceans
• Stroke volume decreases concomitant with bradycardia in phocid seals, as does CO
• A study in otariids suggested that SV remained near constant during diving and CO decreased only due to the bradycardia
• May be species differences or just different circumstances/study designs
• Bradycardia observed during voluntary diving can be less pronounced and more variable than in forced submersion experiments
  
  • Sometimes heartrates are not much lower than resting HR
• Diving bradycardia is stimulated by peripheral receptors and mediated through trigeminal stimulation, though cortical feedback and control is evident as well
• Tachycardia often occurs during resurfacing in anticipation of re-oxygenation
• HR can also decrease just before submergence, indicating there is cognitive control
• Another study showed sea lions can be trained to reduce their HR in response to an auditory cue, furthering the evidence of cognitive control
• dive bradycardia is graded and variable in response to exercise-induced demands for increased peripheral tissue perfusion, ie swim speed while diving etc
• degree of bradycardia appears to be species specific

Question 5

How does the dive response affect the distribution of blood?

How does it change peripherally?

How does it change to the brain?

How does it change to internal organs?

Answer 5

Blood flow redistribution

• Dive-induced peripheral vasoconstriction redistributes blood flow from peripheral splanchnic, muscular, and cutaneous tissues, so that blood flow to more oxygen-demanding tissues (eg brain and heart) can be maintained
• Accompanied by a maintenance or increase in central arterial BP
• Variable among species
• Some species of pinnipeds reduce or completely diminish bloodflow to the spleen, liver, and kidneys as well
• Bradycardia is not necessary for occurrence of peripheral vasoconstriction
• Vasoconstriction likely mediated by high sympathetic tone, even overriding vasodilatory signals from metabolic end products that result from oxygen deprivation of the muscle tissues
• Blood flow to the brain and heart is maintained, conflicting evidence as to whether the flow rate is less, the same, or more than pre dive rates
• The aortic bulb of seals is thought to play a role in blood distribution and maintenance of ABP
  
  • A similar anatomic adaptation has been found in some but not all cetaceans

Question 6

How do marine mammals conserve oxygen during a dive?

How does lactic acid accumulate during a dive?

What is the aerobic dive limit?

Answer 6

Oxygen Economy

• Diving animals exhibit a reduced oxygen consumption while diving and a post-dive release of lactic acid, the occurrence of which was inversely correlated with arterial oxygen tensions, but which did not occur until oxygen tensions had decreased below a certain point
• These findings indicated the accumulation of an oxygen debt, with the release of lactic acid into the general circulation not occurring until breathing and the reoxygenation of blood resumed.
• Aerobic dive limit (ADL) is the term coined to represent the threshold at which the lactic acid increases substantially

Question 7

How is the dive response physiologically controlled?

What nerve structures play a role?

What role do catecholamines play?

Answer 7

Physiologic control of the dive response

• Nervous system control
  
  • Stimulation of the facial branches of the trigeminal nerve during diving contributes to the dive response by serving as the afferent pathway of the reflex arc, which outputs to the vagus nerve
  • Cortical control is also involved
  • cardiac reflexes stimulated by carotid body receptors are also a critical control point in the management of bradycardia while divin
• Hormonal regulation
  
  • Norepi and epi have both been found to significantly increase in the blood of diving pinnipeds
  • Increase in catecholamines strongly associated with splenic contraction and increased Hct as well as increased reliance on anaerobic metabolism
  • Blood flow to the adrenals is also maintained (but reduced) during diving, supporting the evidence of continued release of catecholamines during diving

Question 8

Describe the decision to euthanize a stranded marine mammal.

What considerations for human safety, supportive care for the animal, and prognostic indicators may help with the decision?

What exam findings may warrant euthanasia?

Answer 8

1. Euthanasia = “ending of life of an individual animal in a way that minimizes or eliminates pain and distress”
   
   1. Human safety = top priority
      
      1. Use PPE (gloves, wet suits, closed-toe footwear, helmets)
      2. Have ways to disinfect things
      3. Use Luer lock syringes
   2. Consider euthanasia when animal welfare is compromised and is unable to be restored
2. Supportive Care and Hospice
   
   1. Ensuring breathing (blowhole is free of debris)
   2. Appropriate posture = sternal recumbency, fins/flukes in anatomically neutral position
   3. Shade or sun protection
   4. Temperature regulation
   5. Minimal handling
3. Stranded Animals
   
   1. Stranded cetacean/manatee = on land in shallow water or out of normal habitat and unable to return
   2. Stranded pinniped/sea otter/polar bear = onshore and unable to return or in need of medical care
   3. Exam findings that warrant euthanasia:
      
      1. Vertebral fractures
      2. Large wounds
      3. Penetrating wounds into thoracic or abdominal cavities
      4. Large amount of scavenging/blistering or affecting eyes/blowhole
      5. Significant hemorrhage from the mouth, blowhole, genital opening, anus
      6. Loss of reflexes at the eyes, tongue, blowhole, genital opening, anus
      7. Prolonged hypothermia or hyperthermia

Question 9

What sedatives should be used for pre-euthanasia sedation?

What are teh advantages and disadvantages of chemical euthanasia of mrainre mammals?

What routes of administration are available?

What drugs are available for euthanasia? What are the pros and cons of each?

Answer 9

1. Pre-Euthanasia Sedation and Analgesia
   
   1. IM injections with midazolam, diazepam, acepromazine, xylazine, meperidine, butorphanol, etc
   2. Xylazine and acepromazine are not controlled
   3. Excitation may occur with alpha-2 agonists alone, so use them in combo with something
   4. Commonly used:
      
      1. Meperidine 4 mg/kg IM
      2. Acepromazine 0.2-1 mg/kg IM + xylazine 2-4 mg/kg IM +/- midazolam 0.05-0.1 mg/kg IM
2. Methods of Euthanasia
   
   1. Chemical
      
      1. Disadvantages: need for physical or chemical restraint, difficult vascular access, excitement phase, need for specialized delivery systems (long needles)
      2. Advantages: Socially accepted
      3. Estimate weight based on length
      4. Intravenous access: ventral peduncle, intracardiac (when anesthetized)
      5. Intraperitoneal or intrahepatic are also routes
      6. Intramuscular with ultra-potent opioids may be successful but have issues with residues
      7. Intranasal in blowhole?
3. Euthanasia Drugs:
   
   1. Barbiturates
      
      1. Pros: single agent anesthesia, rapid loss of consciousness, IP route is acceptable
      2. Cons: controlled (DEA II), residues are toxic to scavengers
      3. Pentobarbital 80 mg/kg IV
      4. Can reduce volume needed with premedication
   2. Ultrapotent Opioids (etorphine, carfentanil)
      
      1. Pros: Small volume, rapid onset, no IV access needed
      2. Cons: scavenger toxicity, human exposure risk, require special DEA approval
   3. T-61 = local anesthetic, hypnotic, curariform drug
      
      1. Cons: IV only, paralysis before unconsciousness?, scavenger toxicity, controlled
   4. Potassium Chloride
      
      1. MOA = cardiotoxicity
      2. Pros: low-residue, inexpensive, no histo artifacts
      3. Cons: Requires two-step, arching and gaping occur, IV or intracardiac, large volume
   5. Paralytics?
   6. Inhalants?

Question 10

What physical methods of euthanasia are available for marine mammals?

What are teh pros adn cons of each?

How should carcasses be disposed of? What considerations need to be made regarding the carcass?

Answer 10

1. Physical Methods
   
   1. Methods that can only be used under anesthesia: exsanguination, suffocation, thoracotomy, gunshot to heart
   2. Often very quick but look ugly
   3. Ballistics
      
      1. Gunshot to brain or brainstem causes immediate loss of consciousness
      2. May work in small cetaceans (<8 m, through blowhole or lateral)
      3. Do NOT use buckshot of 0.22-caliber rifle
      4. Do use 12 g shotgun with 28 g lead slug
   4. Explosives
      
      1. Place charge caudal to blowhole and sandbag to direct down or in mouth
      2. Grenade harpoons can be used in whaling
   5. Exsanguination
      
      1. Only in unconscious animals
      2. Can be visually unappealing to public
      3. Cut major vessels in axillary space or intercostal cut to cause intrathoracic hemorrhage
2. Carcass Disposal
   
   1. Small carcasses can be transported for burying, composting, incinerating, etc.
   2. Large carcasses can be left alone, buried on site, towed to seal
   3. Consider residues and risks to scavengers