Farm Animal Anesthesia. Группа авторов

vessels and their skin is usually dark colored. In large adult pigs with proper restraint, a central dorsal ear vein can be used for IV injection and/or catheterization. An 18‐ or 20‐gauge, 1‐ to 1½‐in. hypodermic needle or butterfly catheter can be used for large adult pigs. A 21‐ or 23‐gauge butterfly catheter will be suitable for smaller‐sized pigs with small ears. This author prefers a butterfly catheter because it has a shorter needle and tends to stay in the vessel better than hypodermic needles, especially when the animal struggles during injection. Shorter needles are easier to hold in place and decrease the chance of perivascular injection. IM injection of anesthetics or anesthetic combinations to pigs has been shown to produce short‐term anesthesia effectively. Always keep in mind that pigs have a thick subcutaneous layer of fat, and thus, to ensure the drug is deposited into the muscle, a longer needle (≥1½ in. for large, mature pigs; 1 in. for piglets) should be used [23].

Tracheal intubation is somewhat difficult in ruminants, camelids, and pigs. Blind intubation as in horses is less likely to be successful. For large ruminants, this author's preference is to use digital palpation to guide the endotracheal tube into the trachea immediately following induction of anesthesia with the animal in either sternal or lateral recumbency (Figure 1.4a). Another technique involves use of a stomach tube as a stylet with the aid of digital palpation to place the stomach tube in the trachea; the stomach tube then serves as a guide tube (Figure 1.4b). The endotracheal tube is threaded into the trachea and the stomach tube removed once the endotracheal tube is in place. Intubation should be performed immediately after induction. In calves, intubation is easier when placing the animal in sternal recumbency and an assistant pulls the mouth open by placing a loop of gauze around the upper jaw and a second loop around the lower jaw and tongue. An assistant should lift the head and keep the head and neck in a straight line to allow visualization of the epiglottis and the larynx. If the larynx cannot be visualized, the neck should be extended further. A long laryngoscope blade (250–350 mm) can be used to suppress the tongue base and epiglottis to enable visualization of the larynx. A guide tube or stylet (preferably a 10‐French, 22‐in.‐long polyethylene canine urethral catheter that is three times the length of the endotracheal tube) can be used (Figure 1.5). A cuffed endotracheal tube will prevent regurgitation and aspiration of ruminal contents, and the calf should be maintained in sternal recumbency until the cuff is inflated.

      

Figure 1.4 (a) Intubation in an adult bovid using digital palpation technique: A, trachea; B, epiglottis; C, endotracheal tube/guide tube; D, wedge. (b) Intubation in an adult bovid using a guide tube technique: A, trachea; B, epiglottis; C, guide tube; D, wedge.

      Source: Illustration by Kim Crosslin.

Figure 1.5 Guide tube/stylet and laryngoscope used for endotracheal intubation for small ruminants, camelids, and pigs.

Intubation is more difficult in small ruminants and camelids as compared to large ruminants and other animal species because their mouths do not open widely, the intermandibular space is narrow, and the laryngeal opening is distant to the thick base of the tongue (Figure 1.6). In camelids, the presence of glottal folds adds to the difficulty in visualizing the epiglottis. The technique used for tracheal intubation of small ruminants and camelids is similar to the technique used in calves. It is easier when the animal is placed in sternal recumbency immediately after induction of anesthesia. Intubation is best accomplished with the help of a guide tube/stylet and long‐bladed laryngoscope (250–350 mm) as described for intubation in calves. Hyperextending the animal's neck helps visualization of the larynx (Figure 1.7). The method makes endotracheal intubation in small ruminants and camelids much easier to achieve than with other methods. A cuffed endotracheal tube should be used to provide an adequate seal between the tube and the tracheal mucous membrane to prevent aspiration of saliva and regurgitated ruminal contents. The animal should be maintained in sternal recumbency until the cuff is inflated. Blind intubation, similar to that used in horses, has been used for intubation in sheep and goats; however, it may require multiple attempts to successfully place the endotracheal tube in the trachea. Another technique, described as stick intubation, has been used effectively at Auburn University. With the animal in lateral recumbency, a small‐diameter rod made of wood or stainless steel can be used as a stylet to stiffen the endotracheal tube. One hand occludes the esophagus, and the other hand manipulates the endotracheal tube into the trachea (Figure 1.8). Care and gentle maneuvering should be used to prevent initiating laryngeal spasm and to minimize trauma to the oral mucous membrane.

Similar to small ruminants and camelids, pigs' mouths cannot be opened wide, the epiglottis is often entrapped behind the soft palate, and the small larynx slopes downward, creating a sharp angle to the tracheal opening (ventral floor fornix) (Figure 1.9). Laryngeal spasms are easily elicited by repeated attempts at tracheal intubation. Vomiting can also occur if attempting intubation while the pig is under a light plane of anesthesia, especially when the animal is not appropriately fasted prior to anesthesia. Spraying a small amount of local anesthetic to desensitize the larynx will reduce the potential for laryngeal spasm. In larger or adult pigs, tracheal intubation is easier to accomplish with the pigs placed in sternal recumbency. Using the same technique as in small ruminants and camelids, with the aid of laryngoscope and guide tube/stylet, the epiglottis and laryngeal aperture can be visualized. Be aware of the sharp angle between the larynx and tracheal opening; it is helpful to apply some pressure to the end of the endotracheal tube as it enters the larynx. This technique keeps the tip of the tube slightly elevated and enables the endotracheal tube to pass into the trachea. Another helpful tip for successful endotracheal intubation in pigs is to spin the tube 180° or in a screwlike fashion, advancing it in a dorsal direction while the tube passes through the arytenoid cartilages into the trachea [68].

Figure 1.6 Anatomic structures for endotracheal intubation in camelids.

      Source: Illustration by Kim Crosslin.

Figure 1.7 Endotracheal intubation in anesthetized goats.

Figure 1.8 “Stick intubation” (blind intubation) in anesthetized goats.