Advantages and guidelines for using opioid agonists for induction of anesthesia.

Opioids have a central role in the anesthetic management of small animals, as premedicants, as part of a balanced anesthetic technique, or for the provision of postoperative analgesia. These drugs are safe to use, provide excellent analgesia, and are easily reversible. They cause minimal cardiovascular depression and induce no deleterious renal or hepatic changes. These agents, combined with a sedative, generally provide an ideal anesthetic state.     

Precautions when using opioid agonist analgesics.

Opioid agonist analgesics are effective drugs for treating postoperative pain. Contraindications for their use are primarily respiratory depression and increased intracranial pressure. Their use may mask potentially serious postoperative complications.     

Precautions when using opioid agonist-antagonist analgesics.

Agonist-antagonists are attractive because of their availability and absence of strict regulation. They do provide effective analgesia in many cases, and they are cost-effective. Incomplete analgesia can be noted in moderate to severe pain. Cardiopulmonary depression may be noted following agonist-antagonist administration. Interference with coadministered opiate agents may occur.     

Precautions when using mask induction.

There are few techniques as frequently employed in veterinary anesthesia that are more dependent on good clinical judgment, technical skill, and finesse than mask induction. The technique can be extremely valuable in selected patients.     

Precautions when using alpha-2 agonists as anesthetics or anesthetic adjuvants.

Alpha-2 adrenergic agonists have some unique properties that could theoretically make them useful in the perianesthetic period: they reduce the MAC of inhaled anesthetics, and they are reversible. They also have properties that may limit their usefulness, such as marked decreases in cardiac output. Their clinical utility awaits further studies.     

Precautions when using halothane.

Halothane is a potent inhaled anesthetic that is used extensively in veterinary practice. Certain properties and side effects warrant careful monitoring of patients anesthetized with it and may preclude its use in certain individuals.     

Precautions when using enflurane.

Enflurane offers few advantages over halothane, and it is more expensive than halothane. It causes greater cardiopulmonary depression and induces seizure activity. When economy and systemic effects are considered, enflurane offers no real benefits for veterinary anesthesia.     

Precautions when using antiprostaglandins.

Antiprostaglandins are effective for relief of pain of low to moderate intensity. The majority of these agents interfere with clotting function, and they should not be used on animals with potential coagulopathies. With high dosage or long-term treatment, gastrointestinal irritation and ulceration are probable. NSAIDs should not be used in conjunction with methoxyflurane because of the potential for renal damage. Care should be taken to avoid hypotension with any anesthetic to obviate renal complications.     

Advantages and guidelines for using ketamine for induction of anesthesia.

Ketamine in combination with a sedative or tranquilizer is a relatively safe and effective drug for intravenous induction of anesthesia in dogs and cats. If properly dosed, the combination can be used to induce anesthesia with minimal adverse cardiovascular effects, and it is a reasonable method for induction of anesthesia in patients with cardiac disease. If dosage is kept low, the rate of recovery is acceptable, and some of the drugs commonly used in the regimen with ketamine are reversible with appropriate antagonists.     

Advantages and guidelines for using ultrashort barbiturates for induction of anesthesia.

Despite the introduction of a number of new injectable agents, ultrashort barbiturates continue to be popular. Some of the reasons include rapid, smooth onset of action; predictable hypnotic effects; relatively rapid, smooth recovery; and inexpensiveness. Ultrashort barbiturates also possess some pharmacodynamic properties that make them ideal agents for use in patients with certain diseases or undergoing certain procedures. These include patients with raised intracranial pressure, patients with a history of seizures, patients with corneal lacerations or glaucoma, patients for examination of vocal cord and arytenoid cartilage function, patients with hyperthyroidism, and patients thought to be susceptible to malignant hyperthermia.     

Pros and cons of using alpha-2 agonists in small animal anesthesia practice

The alpha-2 agonists have been used in veterinary practice for over 30 years following the introduction of xylazine (ROMPUN, Bayer Corp., Shawnee Mission, KS) in 1962. The decision to use alpha-2 agonists in anesthesia practice should be based on factors including patient disposition, presenting complaint, type of procedure, and the veterinarian's familiarity with the drug. Controversy surrounds the issue of using anticholinergic agents concurrent with the alpha-2 agonists. Patient selection and procedure type can aid in determining when use of an anticholinergic with the alpha-2 agonist is advantageous. Antagonism of alpha-2 agonists can be readily accomplished. Commonly, alpha-2 agonists are used in combination with other agents to provide neuroleptanalgesia or sedation prior to general anesthesia.     

Advantages and guidelines for using opioid agonist-antagonist analgesics.

The opioid agonist-antagonists are not controlled substances requiring strict record keeping and security because of their low abuse potential. They are effective analgesics in their own right and can be used to antagonize opioid agonist-induced depression while retaining a degree of analgesia. Respiratory depression is less than that induced by opioid agonists, but degree of analgesia is somewhat limited also owing to the ceiling effect.     

Median effective dosage of propofol for induction of anesthesia in dogs.

The median effective dosage (ED50) of propofol for induction of anesthesia was determined in 25 dogs premedicated with acepromazine, 0.05 mg/kg of body weight, and in 35 unpremedicated dogs. The ED50 was found to be 2.2 mg/kg in premedicated dogs and was 3.8 mg/kg in unpremedicated dogs. The mean +/- SD total dosage of propofol required to induce anesthesia in premedicated animals was 2.8 +/- 0.5 mg/kg and was 4.7 +/- 1.3 mg/kg in unpremedicated animals. Signs of excitement were observed in 5 of the unpremedicated dogs, but in none of those that were premedicated.