abstract

Anesthesia is a reversible, controlled, drug-induced intoxication of the central nervous system in which the patient neither perceives nor recalls noxious or painful stimuli. The most common complications associated with anesthesia include hypotension, hypoventilation, hypothermia and bradycardia. Hypoxemia may develop if the anesthetized animal does not receive supplemental oxygen.

The term "balanced anesthesia" refers to the use of an optimum mixture of drugs, such that the advantages of small amounts of drugs are applied without having to contend with the disadvantages of large doses of any one drug. The analgesic and anaesthetic-sparing properties of these drugs allow reduced concentrations of volatile agents and thereby less cardiovascular depression. They also decrease the stress response and the postoperative morbidity and mortality is also reduced. Balanced anesthetic drug combinations agents include anticholinergics, local and regional anesthetics, opioids, phenothiazine tranquilizers, benzodiazepine tranquilizers, alpha-2 adrenergic agonists, and dissociative anesthetics.

The International Association for the Study of Pain defines pain as an unpleasant sensory and emotional experience associated with actual or potential tissue damage. The inability to communicate does not negate the possibility that an individual animal is experiencing pain and is in need of appropriate pain-relieving treatment.

In aquatic animal medicine we are offered a challenge in the diversity of animals we treat from fish to marine mammals and certain species (like the bluefin tuna) that have some physiological properties of both. A balanced anesthesia combination should be methodically considered in each aquatic species because this allows us to perform techniques, protocols, and surgeries with low morbidity and mortality that would not be otherwise possible.

This paper will discuss the current anesthesia in most of the aquatic animals in order to stimulate the optimum anesthesia and analgesia in our species. Monitoring is an integral part of anesthesia in aquatic animal medicine. For example when an intramuscular anesthetic was needed to safely remove a sea otter from the modified gill nets and implant transmitters, the opioid fentanyl was used which produced a short induction, analgesia, immobility and the ability to reverse the drug for an immediate release. The addition of diazepam, a benzodiazepine tranquilizer, less fentanyl needed to be used to achieve the same level of anesthesia. Since midazolam is water soluble and not oil soluble it can be given intra-muscularly, it is a better drug in combination with fentanyl and has led to a more balanced anesthetic.

Another example is in fish anesthetics, ketamine is useful to remove a fish from a large tank or ocean net because it is short-acting and easily administered. The combination of medetomidine and ketamine, reversible with atipamezole produced a safe, effective anesthesia that reduced the dose of the dissociative anesthetic and produced a more balanced anesthesia. The dose of ketamine is reduced in elasmobranchs. Would the addition of the benzodiazepine tranquilizer midazolam provide a more balanced anesthesia in combination with ketamine and medetomidine? This should be methodically researched.

Several factors affect the rate of induction and depth of anesthesia in fish. These include individual and species variation, size, water temperature, water acidity and whether the injection was placed in red or white muscle. Significant interspecies variation can be expected between teleosts and elasmobranchs.

acknowledgements

University of California, School of Veterinary Medicine, Don Low Fellowship in Anesthesiology.