Complications in Equine Surgery. Группа авторов

is administration of fluids through a nasogastric tube. Less common routes of administration include rectal enemas, or through fistulas in the large intestine. The former can cause severe injury to the rectum and discomfort to the horse and the latter is associated with complications due to the surgery for fistulation, which is invasive and costly.

      Complications Due to Administration Setup

       Definition

      Nasal trauma or aspiration pneumonia due to inadvertent administration in the trachea/lungs

       Risk factors

       Use of a large nasogastric tube

       Use of a stiff nasogastric tube

       Inexperienced administrator

       Pathogenesis

      Mechanical trauma; inadvertent administration of fluid or feed material in the trachea/lungs

       Prevention

      A small‐bore tube can be used to reduce trauma. Use a feeding tube with guidewire, which can be left in place for several days/weeks – if such a feeding tube is used, the guidewire should be shorter than the tube to avoid trauma from the tip of the wire. Lubricant should be placed on the tube before insertion. Insertion of the tube in the trachea is common and needs to be avoided. Palpation of the ventral left neck region and trachea should be performed to ensure correct placement. In some horses (5%) the esophagus is transposed and runs along the right neck region, in which case this side of the neck has to be palpated. A cough reflex is not always elicited by incorrect placement, due to sedation or illness. Endoscopy or radiography can also be used to assess correct placement of the tube. While the tube is advanced in the esophagus, air should be blown through the tube. This is important if a small‐bore tube is used to avoid retroflection of the tube. The tube should ideally end in the distal part of the esophagus rather than in the stomach. This prevents occlusion of the tube with solid ingesta. Large bore indwelling tubes in the stomach have also been shown to delay gastric emptying. The guidewire can be left in place or removed. If it is removed it should not be thrown out, as it might be needed for replacement of the tube. If the tube is left indwelling it should be replaced every 24 hours in the opposite nostril (see Chapter 5: Complications of Nasogastric Intubation).

       Diagnosis and clinical signs

      Diagnosis of nasal trauma is made based on clinical signs such as nasal discharge or bleeding and can be confirmed via endoscopy. Diagnosis of aspiration pneumonia due to inadvertent administration of enteral feeding into the trachea/lungs is based on clinical signs such as fever, coughing and nasal discharge. Endoscopy and cytology of a tracheal aspirate as well as thoracic ultrasonography and radiography can aid in diagnosis.

       Treatment

Nasal mucosal trauma will usually heal without treatment. Discontinuation of nasogastric intubation or using the other nostril can also help. Anti‐inflammatories (flunixin meglumine 1.1.mg/kg q12 h IV) and/or broad‐spectrum antibiotics can be necessary in severe cases. In case of aspiration pneumonia due to inadvertent administration fluids into the trachea, general treatment principles for aspiration pneumonia should be followed. These include anti‐inflammatories (flunixin meglumine 1.1.mg/kg q12 h IV) and broad‐spectrum antibiotics (e.g. gentamicin 6.6 mg/kg q24 h IV and Na‐penicillin 30,000 IU/kg q6 h IV).

       Expected outcome

      Nasal trauma usually heals well over time; in rare cases necrosis of the conchae has occurred (unpublished data). Prognosis for aspiration pneumonia depends on severity; if sterile fluids only are used prognosis is good, if large amounts were administered into the lungs, prognosis can be guarded.

      Complications Due to Volume of Fluid Used

       Definition

      Overhydration and gastrointestinal rupture

       Risk factors

       Small patients (ponies, neonates) where the capacity of the stomach is overestimated

       Horses with reflux

       Horses with gastric impaction

       Pathogenesis

      Similar to intravenous fluid therapy, enteral fluid therapy can lead to overhydration. Experimental administration of large volumes (20 ml/kg/h) has been shown to lead to overhydration [52, 53]. Systemic overhydration depends on the capacity of fluid absorption from the gastrointestinal tract and it is therefore less likely to occur compared to systemic intravenous fluid therapy. See earlier in this chapter for more details.

      Horses have no capacity to vomit due to a strong external sphincter at the cardia. Administration of large amounts of fluid with or without the addition of reflux, leads to overdistension and rupture of the stomach. Colonic rupture is a potential complication of enteral fluid therapy in man. Administration of fluid into the stomach leads to increased colonic motility through the gastro‐colic reflex. In cases of severe impaction, this could lead to a colonic rupture. However, this has not been reported in horses [54, 55]. Cecal ruptures after enteral fluid therapy for cecal impaction have rarely been reported [56].

       Prevention

      Enteral fluids can be administered as a bolus or as a continuous rate of infusion. If a bolus infusion is used, the maximum amount to be administered has to be taken into account. The volume of the stomach of a 450 kg horse is approx. 8–15 L. Administration of more than 8 L is not recommended. Amounts have to be adjusted to body weight. If continuous rate infusion is chosen, the rate should be gradually increased from 5 ml/kg/h initially, to a maximum of 15 ml/kg/h, to avoid signs of abdominal discomfort. The stomach needs to be assessed for reflux before administration. The horse’s reaction and vital parameters should be checked during administration to avoid over distention of the stomach.

       Diagnosis and clinical signs

      If tachycardia, tachypnea or signs of colic occur, administration should be discontinued. If signs persist, a large bore nasogastric tube should be placed to check for reflux.

       Treatment

      Discontinue enteral fluid therapy and empty the stomach by nasogastric intubation.

       Expected outcome

      If gastric distension is relieved on time, the prognosis is good. If the stomach ruptures due to volume overload, the prognosis is grave.

      Complication Due to Type of Fluid Used

       Definition

      Severe electrolyte abnormalities

       Risk factors

       Use of tap water (hyponatremia) [57]

       Custom‐made electrolyte solutions with low sodium concentrations

       Pathogenesis

      If large amounts of tap water are administered over a prolonged period of time, plasma sodium concentrations will decrease due to dilution. Inadvertent administration or false mixing of fluids and electrolytes of fluids, e.g. 9% NaCl, can also lead to severe hypernatremia and neurological signs. Additional electrolyte abnormalities reported after excessive doses include hypomagnesemia and hypocalcemia [52].

       Prevention

      If