LITMIR.BIZ

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].