The case for qualitative anesthesia.

Qualitative anesthesia is an effective, time-honored, familiar, and simple technique for maintaining general anesthesia. There is no reason to change.     

The case for maintenance of general anesthesia with an inhalational agent.

Control of anesthetic depth is the primary advantage of general anesthesia with inhalational anesthetics as opposed to injectable agents. In addition, inhalational anesthetics provide good intraoperative stress reduction, adequate muscle relaxation, and an elimination pathway (lungs) independent of liver and kidney function. There is little postoperative respiratory depression and no rebound effect, which is sometimes seen with injectable anesthetics. The incidence of anesthetic-related toxicity is rare and is not considered a problem.     

The case for maintenance of general anesthesia with an injectable agent.

The maintenance of anesthesia with injectable drugs provides a safe alternative to inhalant techniques, provided that the basic needs of the patient are met. The standard drugs (e.g., thiobarbiturates, methohexital, ketamine) can be used, economically and safely, to provide a short duration of anesthesia, but the best drugs for more prolonged procedures are more expensive (e.g., alfentanil, fentanyl, propofol) and require more sophisticated equipment to provide optimal conditions.     

Ketamine-paraldehyde anesthesia for rabbits.

Combination of ketamine hydrochloride (50 mg/kg) and paraldehyde (0.5 ml/kg), both administered intramuscularly, was found to be safe and effective for induction and maintenance of anesthesia for prolonged major surgical procedures in rabbits. Time of induction of deep surgical anesthesia was 20 to 30 minutes. Surgical procedures (creation of intestinal loops for perfusion studies) lasting 3 to 4 hours were performed, with an additional dose of ketamine (25 mg/kg) occasionally being given after 2 hours. At the end of the experiments, rabbits were killed. Another group of rabbits was maintained in a deep surgical plane of anesthesia for 5 hours without any surgical operation being done. Rabbits were then allowed to recover and, on the next day, were again anesthetized and allowed to recover without the performance of surgical operation. Finally, after a day's hiatus, the same rabbits were used in intestinal perfusion experiments. The use of 2 complementary anesthetics, each with a wide margin of safety for respiratory centers, provided safe anesthesia. The ability to administer a relatively fixed dose obviated the need for inordinate expertise to anesthetize rabbits for long periods.     

Protocols for anesthesia of cattle.

The article explores the choices and considerations pertinent to the selection of an anesthetic protocol for use in cattle. When the veterinarian is presented with the opportunity to provide anesthesia for surgical or diagnostic procedures, the options include use of local anesthetics, sedative-tranquilizer and analgesic combinations, or general anesthetic techniques. Informed decisions regarding selection of an anesthetic technique or protocol are made possible with understanding of the perianesthetic considerations commonly recognized for cattle.     

The case for in circuit vaporizers.

In circuit vaporizers have some characteristics that differ from out of circuit vaporizers. In circuit vaporizers are easy to use, effective, and offer several clinical advantages.     

The case for high gas flows.

High gas flows provide a higher margin of safety and fewer physiologic complications for extended anesthetic periods. The veterinarian should consider personnel, anesthetic, and monitoring equipment and the surgical procedure requiring anesthesia before making a final decision on which flow rates are appropriate.     

The case for low gas flows.

When nitrous oxide is not used, there are no clinically significant, valid reasons for not using low gas flows. There are many clinically significant, valid reasons for using low flows.     

The case for routine fluid administration.

Because the risks associated with fluid administration are small, but the effects of fluid withdrawal during anesthesia can be significant, routine fluids should be considered in all cases in which general anesthesia exceeds 45 minutes.     

Quantitative anesthesia.

Quantitative anesthesia is delivering anesthetic and oxygen in known quantities, the dosage based on calculations for their uptake. The uptake is not linearly related to body weight but is linearly related to body weight raised to a power. The dosage of inhaled anesthetics is calculated by the method of Lowe. The oxygen consumption and cardiac output are estimated by formulas that relate physiologic functions to the body weight in kilograms, raised to a power.     

Propofol anesthesia.

Although questions may still remain regarding the use of this unique sedative-hypnotic drug with anesthetic properties in high-risk patients, our studies have provided cardiopulmonary and neurological evidence of the efficacy and safety of propofol when used as an anesthetic under normal and selected impaired conditions in the dog. 1. Propofol can be safely and effectively used for the induction and maintenance of anesthesia in normal healthy dogs. Propofol is also a reliable and safe anesthetic agent when used during induced cardiovascular and pulmonary-impaired conditions without surgery. The propofol requirements to induce the safe and prompt induction of anesthesia prior to inhalant anesthesia with and without surgery have been determined. 2. The favorable recovery profile associated with propofol offers advantages over traditional anesthetics in clinical situations in which rapid recovery is important. Also, propofol compatibility with a large variety of preanesthetics may increase its use as a safe and reliable i.v. anesthetic for the induction and maintenance of general anesthesia and sedation in small animal veterinary practice. Although propofol has proven to be a valuable adjuvant during short ambulatory procedures, its use for the maintenance of general anesthesia has been questioned for surgery lasting more than 1 hour because of increased cost and marginal differences in recovery times compared with those of standard inhalant or balanced anesthetic techniques. When propofol is used for the maintenance of anesthesia in combination with a sedative/analgesic, the quality of anesthesia is improved as well as the ease with which the practitioner can titrate propofol; therefore, practitioners are able to use i.v. anesthetic techniques more effectively in their clinical practices. 3. Propofol can induce significant depression of respiratory function, characterized by a reduction in the rate of respiration. Potent alpha 2 sedative/analgesics (e.g., xylazine, medetomidine) or opioids (e.g., oxymorphone, butorphanol) increase the probability of respiratory depression during anesthesia. Appropriate consideration of dose reduction and speed of administration of propofol reduces the degree of depression. Cardiovascular changes induced by propofol administration consist of a slight decrease in arterial blood pressures (systolic, mean, diastolic) without a compensatory increase in heart rate. Selective premedicants markedly modify this characteristic response. 4. When coupled with subjective responses to painful stimuli, EEG responses during propofol anesthesia provide clear evidence that satisfactory anesthesia has been achieved in experimental dogs. When propofol is used as the only anesthetic agent, a higher dose is required to induce an equipotent level of CNS depression compared with the situation when dogs are premedicated. 5. The propofol induction dose requirement should be appropriately decreased by 20% to 80% when propofol is administered in combination with sedative or analgesic agents as part of a balanced technique as well as in elderly and debilitated patients. As a general recommendation, the dose of propofol should always be carefully titrated against the needs and responses of the individual patient, as there is considerable variability in anesthetic requirements among patients. Because propofol does not have marked analgesic effects and its metabolism is rapid, the use of local anesthetics, nonsteroidal anti-inflammatory agents, and opioids to provide postoperative analgesia improves the quality of recovery after propofol anesthesia. 6. The cardiovascular depressant effects of propofol are well tolerated in healthy animals, but these effects may be more problematic in high-risk patients with intrinsic cardiac disease as well as in those with systemic disease. In hypovolemic patients and those with limited cardiac reserve, even small induction doses of propofol (0.75-1.5 mg/kg i.v.) can produce profound hypotens     

Avian anesthesia.

Providing a safe anesthetic environment is the key to successful avian anesthesia. Knowledge and understanding the anatomic and physiologic differences between birds and mammals help to prevent most emergency situations and guide responses in critical situations. Thorough preanesthetic history and examination, correction of underlying conditions, and use of simple anesthetic protocols all optimize the outcome of the procedure. Finally, critical monitoring helps to anticipate most crises and reduces incidences of mortality and morbidity in avian anesthesia.     

Crocodilian anesthesia.

With declining crocodilian populations worldwide, a greater interest in the conservation of these animals in the wild and in captivity is ongoing. This effort has created a demand for safe and effective ways to handle and immobilize crocodiles for transport and relocation. With the advent of new anesthetic protocols, working with crocodilians has now been made safer for both the animal and the handler. Unfortunately, current anesthetic protocols have been limited to a few species and further application of these protocols need to be undertaken with new species.     

Invertebrate anesthesia.

One hundred years ago (January 5th, 1901), an article in the Veterinary Record declared: The use of chloroform by practitioners is now common, and the amount of pain and suffering prevented is enormous. By its aid we are enabled to perform operations with success which without it were seldom satisfactory. A century later, in an age of sophisticated veterinary medicine, those words seem quaint, a relic of a bygone age. Our understanding of anesthesia of invertebrates in 2000 is very much at a comparable stage, however, and a great deal of research is needed to remedy this situation.