Page 99 - JSOM Spring 2018

stomach’s inlet (esophageal portal) and outlet passageways splenic torsion may occur, leading to avulsion and/or strangu-
(pyloric portal), and strangulate gastric blood supply. Gastric lation of splenic vasculature with resultant splenic thrombosis
inlet and outflow tract obstructions impair the canine's normal and infarction. Intestinal blood flow is impaired, resulting in
mechanisms for promoting gastric emptying (e.g., eructation, increased bacterial endotoxin production and translocation
vomiting, pyloric emptying). This allows air, fluid, and chyme across the compromised intestinal mucosal barrier. 6
to become trapped within the stomach lumen. Strangulation
of gastric blood supply causes gastric venous congestion, re- Pathogenesis
sulting in increased gastric secretion and transudation of fluids The pathogenesis of GDV is not completely understood but is
into the gastric lumen. Ongoing metabolic reactions within the considered to have a multifactorial etiology. Several host and
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lumen (e.g., bacterial fermentation of carbohydrates) contrib- environmental predisposing factors (e.g., genetics, sex, age,
utes to further intraluminal gas accumulation. Collectively, breed, diet, exercise) have been implicated in increasing the
2
these processes exacerbate gastric distention, further impair- likelihood for GDV; however, evidence supporting the relevant
ing gastric blood flow (Figure 2). importance of these risk factors remains inconclusive. 11–16 As
such, it remains unclear what measures are best used to pre-
FIGURE 2 Stomach developing bloat (reproduced with permission of vent GDV.
Veterinary Information Network and www.VeterinaryPartner.com).
Although any breed of canine may develop GDV, it is primar-
ily associated with pure-bred, large and giant breed canines
that possess a deep-chested conformation, particularly those
breeds possessing a high thoracic depth-to-width ratio. 11–16
Most breeds of military and civilian OpK9s, (e.g., German
Shepherds, Belgian Malinois, Labrador retriever) fit this con-
formational description and, therefore, are at high risk for
GDV. 17,18 A review of 927 military working dogs demonstrated
that GDV was one of the five leading causes of death in this
population, consisting primarily of German Shepherds and
Belgian Malinois. The following is a list of risk factors re-
17
peatedly associated with an increased likelihood of GDV 6,11-16 :
genetics: having a history of GDV in any first-degree relative
The intraabdominal effects of GDV have multisystemic effects (i.e., parent, sibling, offspring); age: advancing age (between 4
that cause a cascade of events that, in turn, result in multi- and 5 years old); sex: male dogs (neutered or not); personal-
organ dysfunction. Gastric distention causes intraabdominal ity traits: hyperactive, fearful, stressed, nervous, or aggressive
pressure (IAP) to rise to the point of impeding venous blood temperament; and body condition and anatomic factors: lean
flow within abdomen (i.e., caudal vena cava, portal vein, body condition (giant breeds), high abdominal depth, high ra-
splenic veins, and splanchnic veins). Intraabdominal ve- tio of thoracic depth to abdominal depth (large breeds), and
10
nous occlusion decreases venous return to the heart, causing high thoracic depth-to-width ratio.
a subsequent reduction in cardiac output, mean arterial pres-
sure (MAP), and systemic-tissue oxygen delivery. Splanchnic Although many dietary factors (e.g., rapidly eating a large
pooling with portal hypertension promotes transcapillary volume of food, especially if fed once daily, eating from an
fluid flux with resultant development of interstitial edema, elevated feed bowl; feeding dry kibble) are commonly impli-
hypovolemia, and, eventually, circulatory collapse. Impaired cated as risk factors for GDV, available evidence regarding
4,6
oxygen delivery further leads to respiratory, central nervous these dietary factors remains questionable at best. Rapid
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system, gastrointestinal, and renal compromise. In one sense, eating is considered to increase the risk of GDV; however, an
the intraabdominal effects of GDV are analogous to that of an analyses of six studies related to the speed of eating found no
abdominal tourniquet. conclusive evidence to support this claim. Similarly, a review
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of six different studies related to feeding dry kibble also found
Gastric distention and elevated IAP have effects beyond im- insufficient quality evidence to support the assertion that feed-
pairing blood flow and oxygen delivery. Respiratory compro- ing a kibble-based diet is associated with an increased risk of
mise ensues as gastric distention and increased IAP reduce GDV. It has also been recommended to feed from an elevated
20
total thoracic volume and impede normal caudal diaphrag- food bowl to decrease the likelihood GDV; however, evidence
matic excursion. This decreases tidal volumes, promotes at- shows that feeding from a raised food bowl actually increases
electasis, and fosters ventilation-perfusion mismatching. The the incidence of GDV. Finally, postprandial exercise has been
6
body attempts to compensate with increasing respiratory rate considered a predisposing risk factor for GDV risk; yet, sub-
and effort; however, these compensatory mechanisms quickly sequent evidence actually indicates light exercise after eating
become inadequate and hypoxemia and hypercapnia (hy- decreases the risk. 21
poventilation) follow. The short gastric arteries arise from the
splenic artery and supply the greater curvature of the stomach. Preventive Measures
Compression, thrombosis, and avulsion of the short gastric With the aforementioned lack of understanding of the patho-
arteries lead to gastric wall infarction and necrosis; left un- genesis and undocumented evidence supporting the impor-
attended, gastric wall perforation and subsequent peritonitis tance of predisposing risk factors for GDV, most preventive
may develop. 6,11 Gastric necrosis carries a high mortality risk measures are empirical and anecdotal. Despite not having any
in canines. Avulsion of the short gastric arteries may also re- documented proven benefit for reducing the incidence of GDV
4
sult in significant intraabdominal hemorrhage. Due to the in at-risk breeds, the following are recommended preventive
4
close anatomical association between the stomach and spleen, measures that are continually used: feeding multiple small
Prehospital Care of Canine Gastric Dilatation and Volvulus | 93