Injectable Anesthesia and Analgesia of Birds

Isoflurane is the anesthetic of choice for most avian anesthetic procedures. However, inhalation anesthesia is not always available in field situations involving wild birds, although small portable inhalation anesthesia units are available. Certain surgical procedures, such as tracheal resection, may warrant the use of injectable anesthesia regardless of whether or not an anesthesia machine is available [1]. Anesthetic gases can escape from the bird during surgical procedures that disrupt air sacs, or the extension of air sacs into pneumatic bones, and thereby expose staff to anesthetic gases. Advantages of injectable anesthetic agents include rapid administration, low cost, and minimal equipment. Some anesthetic agents can be reversed, an important advantage when working in field situations. Injectable anesthetics are frequently used in large, long legged birds, such as ratites, when physical restraint is impossible or dangerous. Injectable anesthetics used in birds include barbiturates, chloral hydrate, alpha chloralose, phenothiazines, dissociatives, alpha-2 adrenergic agonists, alphaxalone/alphadolone and propofol [2]. Some of these anesthetics, such as barbiturates, chloral hydrate, alpha chloralose and alphaxalone/alphadolone, are no longer recommended and will not be discussed here. The greatest disadvantage of injectable anesthetics is individual and species variation relative to drug dose and response to a specific drug. Elimination of an injected drug depends on distribution, biotransformation and excretion. While we recognize species differences within domestic animals and tailor drug and dose accordingly, we nonetheless tend to treat all birds as if they belonged to one genus or species; as if, for instance, the pigeon is the same as an ostrich when in fact these two birds are as phylogenetically different from each other as the horse is from the cat. Pharmacokinetic studies of antimicrobial drugs in different species of birds have shown that kinetics vary significantly between species and even between birds of the same order such as cockatiels and Amazon parrots (both Psittaformes). Therefore data collected on an injectable anesthetic using a pigeon may not be directly transferable to another species of bird. Nevertheless, information collected on one avian species is likely to be better for extrapolation to another avian species than are data from mammalian species. It is important that the overall clinical condition of the bird be considered during selection of an anesthetic protocol. Precise body weight in grams is essential for accurate dosing. When using injectable anesthetics for birds it is difficult to maintain a surgical plane of anesthesia. The risk of cardiopulmonary depression is high and warrants careful monitoring during an anesthetic procedure. Orotracheal intubation of the anesthetized patient allows for supplemental oxygen and positive pressure ventilation if needed. A ventilation rate of 2 breaths per minute assists the spontaneously ventilating bird. When birds are apneic, the ventilatory rate should be 10 15 breaths per minute. In the bird, both inspiration and expiration require skeletal muscle activity and most anesthetics depress muscular activity, thus reducing air flow rate and oxygen exchange. Assisted or controlled ventilation ensures air flow and improves gas exchange at the level of the parabronchus and air capillaries. Intubation provides a patent airway that permits easy control of ventilation in emergency situations. Nevertheless, intubation is not recommended in very small birds because dried mucus may obstruct very narrow endotracheal tubes and the endotracheal tube may increase resistance to airflow because of a significant decrease in tracheal diameter. It is recommended to calculate and prepare doses of standard emergency and supportive drugs such as epinephrine, doxapram, lidocaine, and atropine before inducing anesthesia. The small size of many avian patients requires accurate dosing of very small volumes or dilution of standard concentrations. Having these drugs prepared and in labeled syringes saves time and anxiety in critical situations. Rapid anesthetic recoveries are best for birds. Birds appear very disoriented during recovery and tend to flap their wings and twist their head and neck. Holding the patient in a light towel wrap or rolling the bird into a loose newspaper "burrito" provides mild restraint to prevent chaotic body movements. Keeping the bird in a warm, quiet, dark place also aids a smooth recovery.