Читать книгу Complications in Equine Surgery - Группа авторов - Страница 62

Definition

Aspiration pneumonia in this circumstance is caused by administration of enterally administered fluids or medication into the lung.

Risk factors

 Improper technique

 Inadequate restraint

 Incomplete passage into the stomach

 Improper removal of the tube

Pathogenesis

Administration of fluid into the lungs can be a consequence of misplacement of a tube into the trachea or it may result from spillage from a properly placed nasogastric tube. The severity of the resulting pulmonary pathology depends on the type and volume of fluid that enters the lung. There are several mechanisms by which nasogastric procedures can result in aspiration pneumonia. First, the nasogastric tube may be misplaced into the trachea by improper technique, inadequate restraint, or by impaired swallowing reflexes in obtunded patients (Figure 5.1) [12]. Second, incomplete passage of the tube into the stomach or esophageal intubation may allow reflux of administered medication or fluid from the esophagus and into the trachea [12]. Third, rapid administration or administration of a large volume of fluid or medication into an already filled stomach can result in esophageal reflux and aspiration of that reflux into the lungs [12]. Fourth, failure to completely empty the tube, failure to kink or occlude the tube while removing, or rapid removal of the tube may allow any residual fluid or medication within the tube to spill into the nasopharynx where it can be aspirated [12].

Figure 5.3 Intraoperative photograph showing the removal of a large nasogastric tube fragment (1.3 cm diameter, 90 cm long) through a full thickness enterotomy in the right dorsal colon. This horse presented with acute signs of colic, but had no known history of prior nasogastric intubation complications. It was presumed that the nasogastric tube fragment had been acquired prior to the current ownership of the horse and did not cause problems until it migrated to the transverse colon and caused obstruction.

Source: Courtesy of Isabelle Kilcoyne.

Prevention

Prevention of inadvertent administration of fluids into the lungs is an essential part of nasogastric intubation procedures. Please refer to the section describing misplacement of nasogastric tubes for specific preventative procedures. Careful attention to all precautions throughout the nasogastric intubation procedure will help to minimize complications.

Diagnosis

Development of respiratory distress immediately following a nasogastric tube procedure is highly suggestive of inadvertent pulmonary administration of fluid. Signs may be delayed by a few days in cases with a small amount of mineral oil aspiration. Diagnosis of contamination of the lungs with mineral oil, also described as mineral oil‐induced pneumonitis or lipoid pneumonia, is based on a history of mineral oil administration, radiographic or ultrasonographic evidence of pneumonia, and the identification of oil in tracheal wash or bronchoalveolar lavage samples [13–17].

Treatment

If a small amount of clean water is inadvertently administered into the lungs, the horse should be placed on anti‐inflammatory treatment and antimicrobial therapy to prevent pneumonia [1]. Administration of larger volumes of fluid may require additional supportive care, such as furosemide to treat pulmonary edema, bronchodilators, and intranasal oxygen therapy. Inadvertent intratracheal administration of certain medications (e.g. deworming drenches) [12] and mineral oil [13, 15–19] may have fatal consequences, even with aggressive treatment. These horses should be aggressively treated with antimicrobial therapy, anti‐inflammatory medications, bronchodilators, nebulization, and intra‐nasal oxygen [13–17]. Repeated bronchoalveolar lavage and lung lobectomy has been reported to be helpful in people with mineral oil aspiration, but it has not been described in the equine case reports [16, 17]. There is one report of successful treatment of lipoid pneumonia, from aspiration of mineral oil, in which dexamethasone treatment was used [14]; however, other authors have reported use of corticosteroids as part of their treatment efforts in cases with unsuccessful outcomes [15].

Expected outcome

A small amount of clean water inadvertently administered into the lungs may be tolerated; however, the horse should be placed on prophylactic treatment to prevent pneumonia [1]. In contrast, a small amount of mineral oil aspirated into the lungs in nearly invariably fatal [13–17].