Small Animal Surgical Emergencies. Группа авторов
Читать онлайн книгу.
1 Fluid therapy to restore intravascular volume.
2 Gastric decompression to reduce the influence of the dilated stomach on venous return.
Management of hypoperfusion is a priority in dogs with GDV. As the cause of hypoperfusion is likely multifactorial, fluid therapy alone may not provide complete stabilization. At the authors' facility, shock doses of isotonic crystalloid fluids (up to 90 ml/kg administered in boluses) or a combination of isotonic crystalloids at a lower dose (20–40 ml/kg) in conjunction with 7% hypertonic saline (2–4 ml/kg) is administered and the dog is then reassessed and fluid therapy is adjusted accordingly. Alternative approaches include the use of a synthetic colloid such as hydroxyethyl starch (hetastarch; 10–20 ml/kg) or 7% hypertonic saline in 6% dextran‐70 (5 ml/kg IV over 5–15 minutes).
The use of hypertonic saline–dextran and hemoglobin solutions (Hb‐200) has been associated with lower doses of fluid administration and shorter time to stabilization compared with lactated Ringer's solution or hetastarch [33, 34]. However, these studies were not significantly powered to show differences in outcome. The use of a synthetic colloids such as hetastarch or 7% hypertonic saline has also been associated with a decreased risk of hypotension [23, 34]. As hypotension has been associated with an increased risk of complications in a number of clinical situations [9, 35], a strategy that would limit the risk of developing hypotension is recommended. In the current market, a number of these fluids (including hetastarch, Hb‐200 solutions and dextran combinations) are no longer readily available. There is evidence in human clinical practice that synthetic colloids are associated with an increased risk of morbidity and mortality [36–38], although this finding has not been identified in dogs [39]. Because of the low mortality rate associated with GDV, identifying whether a type of intravenous fluid therapy is associated with improved survival can be challenging.
Experimental data support rapid transition to surgery following presentation, to minimize the duration of ischemia [26, 40]. However, retrospective analysis has identified increased survival rates with longer periods between presentation and surgery [7]. The authors of this study comment that dogs presenting bright and alert are likely being managed more slowly than those presenting as critically ill, and the authors also found that surgical and anesthesia times were significantly shorter in this study compared with previous studies. Further work is warranted to investigate the relationship between time from presentation to surgery on outcome of dogs with GDV. The time of presentation has recently been shown to be associated with outcome, with dogs presenting between 3 a.m. and 9 a.m. being more likely to die than those presenting between 9 a.m. and 9 p.m. [12].
Prior to gastric decompression, it is useful to obtain abdominal radiographs for a definitive diagnosis. A right lateral abdominal radiograph should be taken initially. Thoracic radiographs should be considered in dogs with dyspnea, to evaluate for the presence of aspiration pneumonia, or in older dogs to identify concurrent disease. Abdominal ultrasonography is not considered useful as it does not aid the diagnosis and will not alter the ultimate plan. Radiographic signs consistent with GDV include a gas‐ and fluid‐filled dilated stomach with displacement of the pylorus and pyloric antrum dorsally. On the right lateral projection, there is a prominent shelf of tissue at the cranial aspect of the stomach giving the classic “reverse C” or “Popeye arm” appearance (Figure 8.2). The presence of intramural gas (pneumatosis) and pneumoperitoneum identified on imaging are specific, but not sensitive findings for gastric necrosis (Figure 8.3) [41]. If these findings are present, then the impact of previous procedures (e.g., trocharization or orogastric intubation) should be taken into consideration, since these procedures may increase the number of false positive results.
Figure 8.2 Right lateral abdominal radiograph showing gastric dilatation and volvulus. Note the “Popeye arm” appearance caused by dorsal displacement of the pylorus.
Figure 8.3 Right lateral abdominal radiograph showing gastric dilatation and volvulus with gastric pneumatosis. This is indicative of gastric necrosis.
Once GDV has been confirmed radiographically, gastric decompression should be attempted. Two methods commonly used are orogastric intubation and gastric trocharization. Orogastric intubation is the more common technique allowing for the removal of gas and fluid but can be more challenging to perform. Trocharization is a simple and rapid technique but allows relief of gaseous distension only. One study reported good success rates for both orogastric intubation (75.5% of dogs) and trocharization (86% of dogs), with no serious complications associated with either technique [42]. The techniques can be used concurrently and may be complimentary. The authors prefer to use trocharization.
To perform trocharization, an area is clipped and surgically prepared dorsally over the abdominal wall in an area of palpable gaseous distension. An area of tympany is identified and a 14‐ or 16‐gauge over‐the‐needle catheter is placed percutaneously into the stomach (Figure 8.4a). The bung is removed, and the stylet can be left in place or removed, allowing gas to escape (Figure 8.4b). If the stylet is left in place, there is less susceptibility to the catheter obstructing due to occlusion, but there is a slightly higher risk of trauma. Once the flow of gas has stopped, the catheter/trochar is removed. Following trocharization, the dog should be taken promptly to surgery and the corresponding gastric wall examined for signs of continuing leakage or necrosis. If an area of concern exists, it should be resected.
A modified technique of ultrasound‐guided percutaneous gastropexy and placement of a gastrostomy catheter has been described to allow continuing gastric decompression prior to surgery [43]. This has been recommended for managing dogs where a delay in surgical treatment is anticipated, for example prior to referral or transfer to another clinic as it allows repeat decompression. The study showed that it was reasonably safe and effective. However, it was similarly effective to repeat trocharization [43].
Figure 8.4 (a) Once an area of tympany is identified, a 14‐ or 16‐gauge over‐the‐needle catheter is placed percutaneously into the stomach. (b) An extension set has been placed into water to evaluate for bubbles to determine when the flow of gas has stopped.
For orogastric intubation, a large‐bore stomach tube with an end hole is lubricated, measured from nostril to last rib (Figure 8.5) and then the length is marked. The dog is placed in sternal recumbency and a roll of bandage with a large enough hole to pass the tube through is placed in the mouth and the mouth held closed around the bandage (Figure 8.6). In alert dogs, sedation or anesthesia may be necessary. Sedation can be accomplished using oxymorphone (0.1 mg/kg IV) or fentanyl (2–5 μg/kg) in combination with diazepam (0.2–0.25 mg/kg IV). In compromised dogs, this combination may be adequate to induce anesthesia. Endotracheal intubation is recommended in anesthetized dogs to protect the airway from aspiration of gastric