Complications in Equine Surgery. Группа авторов

larynx and it is relatively easy to enter the trachea, especially in horses that do not swallow or are resisting the intubation procedure. Retroflexion of the tube into the oral cavity can occur at the leading edge of the tube when trying to enter the esophagus. Alternatively, it may happen along any part of the length of the tube if the esophagus spasms around the tube and prevents its advancement. Further efforts to advance the tube against esophageal resistance results in the pharyngeal part of the tube retroflexing into the oropharynx. Misplacement of the tube in the guttural pouch with subsequent perforation of the medial compartment has been described [4].

Figure 5.1 Lateral radiograph of the pharyngeal region of a miniature horse undergoing a positive contrast esophagogram (black asterisks) showing the nasogastric tube coiled within the guttural pouch (white arrows). The nasogastric tube was subsequently repositioned within the esophagus. The intravenous catheter is labeled (white arrowhead).

      Source: University of California, Davis Veterinary Medical Teaching Hospital Diagnostic Imaging Service.

       Prevention

      Misdirection of the tube into the trachea can be minimized by flexing the horse’s head when the tube is in the nasopharynx. Rotation of the tube by 180 degrees after it has cleared the nasal passages may also be helpful. The tube can be marked with a permanent marker at the distance from the nares to the pharynx/larynx to help judge the proximity of the indwelling tube to the larynx. Retroflexion of the tube into the oral cavity may be minimized by using a tube with sufficient rigidity to reduce abrupt bending of the tube. Tubes with areas of focal weakness should be avoided. Sedation, especially with detomidine [5], may relax the esophagus and aid passage of the tube; however, the horse may have a reduced swallowing reflex. Endoscopic guidance should be considered when smaller diameter nasogastric tubes are placed [4] or if repeated attempts to pass the nasogastric tube have failed.

       Diagnosis

      Although horses may respond to intratracheal placement of the nasogastric tube by coughing, some horses may not exhibit a cough reflex. Absence of coughing does not guarantee correct placement of the nasogastric tube. Intratracheal positioning of the tube can be determined by lack of any resistance to advancement of the tube and free movement of air, if air is blown into the tube or suction is applied to the tube. The tube may be felt to be reverberating within the trachea if the trachea is gently shaken. More importantly, correct positioning of the tube within the esophagus can be confirmed by palpating air boluses within the esophagus when air is blown into the tube and negative pressure is obtained when suction is applied to the tube. Palpation or visualization of the tube within the cervical esophagus ensures correct positioning. If further confirmation is needed, a second individual can auscultate for air bubbling into the stomach by listening over the left 14th intercostal space while air is blown into the tube.

Location of small diameter feeding tubes, which may not be easily palpable, can be confirmed with radiographs (Figure 5.2). Retroflexion of the tube into the oral cavity may be detected by recognizing that the horse is chewing and recognizing that the chewing involves the tube. During misdirection of the nasogastric tube into the contralateral nasal passage, there will be some resistance to passing the tube, but air will move freely in and out of the tube and it cannot be localized in the trachea or esophagus. In the case report describing trauma secondary to misplacement of the tube into the guttural pouch, it was described that initial placement of a nasogastric tube was not able to be advanced beyond the nasopharynx, although subsequent passage of a larger diameter tube was successful. The horse developed signs of throatlatch swelling four hours later, which prompted referral and identification of lesion with endoscopy, ultrasound and radiography [4].

Figure 5.2 Lateral radiograph of the thorax of a neonatal foal to document the position of the indwelling nasogastric feeding tube. In this radiograph, the feeding tube is located within the trachea and extending within a caudal bronchus and into the dorsocaudal lung lobe. Correct esophageal positioning would be evidenced by dorsal positioning of the feeding tube relative to the trachea, especially at the carina (white arrowheads).

      Source: University of California, Davis Veterinary Medical Teaching Hospital Diagnostic Imaging Service.

       Treatment

      As long as intratracheal placement is recognized and corrected before any fluids or medications are administered, there are minimal to no consequences. Erroneous administration of fluid or medication into the lungs is discussed as a separate complication. Retraction of the orally misplaced tube corrects the misplacement; however, the consequences range from abrasion of the tube to cracks or defects in the wall of the tube to complete transection of the tube [5]. In the case report of guttural pouch perforation as a complication of nasogastric intubation, the associated signs of pharyngeal swelling and cellulitis was treated with antibiotics, non‐steroidal anti‐inflammatory drugs, supportive fluid therapy, and feeding of pelleted mashes and soaked hay. Unfortunately, the horse was euthanized several days later due to ulcerative, necrotizing colitis [4].

       Expected outcome

      If promptly recognized and corrected, misplacement of the tube should not be considered a complication. It is merely a consequence of blindly guiding the tube into the esophagus. If misplacement of the tube is not corrected promptly, it can be associated with life‐threatening complications if there is resulting tissue trauma or infusion of medication into the lungs.

Esophageal/Pharyngeal Trauma

       Definition

      Pharyngeal trauma ranges from mild bruising to perforation of the dorsal pharyngeal wall. Esophageal trauma can include ulcerations, linear lacerations, and partial to full‐thickness perforation of the wall at any point along its length.

       Risk factors

       Prolonged durations or repeated intubations

       Horses that resist intubation by retching and contracting their cervical musculature may be at greater risk for complications

       Smaller horse breeds [3]

       Pathogenesis

      Mild pharyngeal trauma and bruising may occur after nasogastric intubation. Pharyngeal perforation has also been described as a complication of nasogastric intubation [7]. Ulceration or perforation of the esophagus is a documented complication of nasogastric intubation. In one study, the primary cause of esophageal perforations was traumatic nasogastric intubation [8]. In another study, esophageal ulceration or perforation was the predominant complication attributed to nasogastric intubation [3]. Pharyngeal and esophageal trauma can occur with a single intubation; however, prolonged durations or repeated intubations appear to be associated with greater risk of complications [3].

       Prevention

      It is proposed that pharyngeal and esophageal trauma might be minimized by selecting smaller